Abstract:
An SMBus message handler, an integrated circuit and a method for controlling an SMBus are disclosed which identifies starting address of a program being stored in a memory. Instructions of the program are fetched one after another into a finite-state machine which controls the data transfer between an SMBus interface and a register set in compliance with the instruction present in the finite-state machine. Further, an SMBus test device and a method for controlling a testing system are described which check as to whether a key is input from a second interface. Upon inputting of a key it is mapped to a sequence of instructions for controlling devices connected to the SMBus or transferring data or receiving data from the devices connected to the SMBus.

Description:
FIELD OF THE PRESENT INVENTION 
     The present invention relates to the field of fabrication of integrated circuits and in particular to integrated circuits and methods implementing SMBus control. According to one aspect of the present invention it specifically relates to an SMBus message handler for managing the data transfer between an SMBus and a register set. According to another aspect of this invention it relates to a method for controlling an SMBus. According to yet another aspect of this invention, it relates to an integrated circuit chip for transmitting and receiving data over an SMBus. According to a further aspect of this invention, it relates to an SMBus test device and a method for controlling a testing system for SMBus chip set validation. 
     DESCRIPTION OF THE PRIOR ART 
     For data exchange between more than two devices various bus systems have been developed. All devices are usually connected to the bus lines. Therefore, only one device at a time may transmit data to one or more other devices connected to the bus and appropriate measures must be taken to make sure that only one device outputs data onto the bus. One measure is the use of tri-state outputs at each device. Another measure is to use open-drain or open-collector output stages and to pull up the bus lines by a voltage. So the outputs of the bus devices, the bus lines and the pull-up resistors form a wired AND function. 
     A system management bus (SMBus) specification is generally known. 
     SMBus is a two-wire bus. Multiple devices, both bus masters and bus slaves may be connected to an SMBus. Generally, a bus master device initiates a bus transfer between it and a single bus slave and provides the clock signals. A bus slave device can receive data provided by the master or it can provide data to the master. 
     The two lines of the SMBus are designated SMBCLK and SMBDAT. Both lines are bi-directional and connected to a positive supply voltage through a pull-up resistor, a current source or another similar circuit. When the bus is free, both lines are high. A master device provides the clock at line SMBCLK. The SMBDAT line is driven either by the master or by the slave depending on the transmission state. Moreover, in compliance with Annex A of the SMBus specification 2.0, two optional lines SMBSUS# and SMBALERT# may be provided. 
     Only one device may master the bus at any time. Since more than one device may attempt to take control of the bus as a master, SMBus provides an arbitration mechanism that relies on the wired AND connection of the SMBus device interfaces to the SMBus. 
     Two unique bus situations define a message START and STOP condition. A high-to-low transition of the SMBDAT line while the SMBCLK line is high indicates a message START condition. A low-to-high transition of the SMBDAT line while the SMBCLK line is high defines a message STOP condition. START and STOP conditions are always generated by the bus master. After a START condition the bus is considered to be busy. The bus becomes idle again after a certain time following a stop condition or after both the SMBCLK and SMBDAT lines remain high for more than Thigh:Max (50 μseconds). 
     Data are transferred bytewise, wherein every byte consists of eight bits. Each byte transferred on the bus must be followed by an acknowledge bit. Bytes are transferred with the most significant bit first. As any other clock pulse, the acknowledge-related clock pulse is generated by the master. The transmitter master or slave, releases the SMBDAT line during the acknowledge clock cycle. In order to acknowledge a byte, the receiver must pull the SMBDAT line low during the high period of the clock pulse. A receiver that wishes not to acknowledge (NACK) a byte must let the SMBDAT line remain high during the acknowledge dock pulse. An SMBus device must always acknowledge (ACK) its own address. An SMBus slave device may decide to NACK a byte other than the address byte, if the slave device is busy performing a real-time task, if data requested are not available, if the slave device detects invalid command or invalid data. 
     The master upon detection of the NACK condition must generate a STOP condition to abort the transfer. Further, if a master-receiver is involved in the transaction, it must signal the end of data to the slave transmitter by generating a NACK on the last byte that was clocked out by the slave. The slave transmitter must release the data line to allow the master to generate a STOP condition. 
     A situation may occur in which more than one master is trying to place clock signals on the bus at the same time. The resulting bus signal will be the wired AND of all the clock signals provided by the masters. A high-to-low transition on the SMBCLK line will cause all devices involved to start counting of their LOW period and start driving SMBCLK low if the device is a master. As soon as a device finishes counting its LOW period it will release SMBCLK line. Nevertheless, the actual signal on the SMBCLK line may transition to the high state of another master with longer LOW period keeping the SMBCLK line low. In this situation, the master that released SMBCLK line will enter the SMBCLK HIGH wait period. When all devices have counted off their LOW period, the SMBCLK will be released and go HIGH. All devices concerned at this point will start counting their HIGH periods. The first device that completes its high period count will pull the SMBCLK line low and the cycle will start again. So, for synchronization purposes, the LOW period is determined by the slowest device and the HIGH period is determined by the fastest device. 
     One or more devices may generate a START condition within the minimum hold time resulting in a defined START condition on the bus. Since the devices that generated the START condition may not be aware that other masters are contending for the bus, arbitration takes place on the SMBDAT line while the SMBCLK is high. A master that transmits a HIGH level, while the other(s) master(s) is/are transmitting a LOW level on the SMBDAT line loses control of the bus in the arbitration cycle. The arbitration may comprise the slave device address, the transfer data, a repeated start, and the following data bits. 
     Besides slave devices which receive or respond to commands, master devices which issue commands, generate the clocks and terminate the transfer, the SMBus specification defines a host device. A host device is a specialized master that provides the main interface to a systems CPU. A host must support the SMBus host notify protocol. There may be at most one host in a system. 
     Any device that exists on the system management bus as a slave has a unique address called the slave address. A slave address comprises seven bits which are completed by a read or write (R/W) bit to a byte. The R/W bit is the least significant bit of the byte. 
     Version 1.1 of the SMBus specification introduced a packet error checking mechanism to improve reliability and communication with busses. Packet error checking is implemented by appending a packet error code (PEC) at the end of each message transfer. Each protocol except for a quick command and a host notifier protocol has two variants: one with the PEC byte and one without. The PEC may be calculated in any way that conforms to 8-bit cycle redundancy check (CRC-8) represented by the polynomial, C(x)=x 8 +x 2 +x 1 +1. The PEC calculation includes all bytes in the transmission including address, command and data. The PEC calculation does not include ACK, NACK, START, STOP nor Repeated START bits. 
       FIG. 1  shows a generic SMBus packet protocol diagram. S designates a start condition, Sr a repeated start condition, Rd an R/W bit having a value of 1, Wr a R/W bit value of 0. An “x” shown under a field indicates that the field is required to have the value of “x”. “A” designates an acknowledge bit position which may have a value of 0 for acknowledgment (ACK) or 1 for non-acknowledgment (NACK). “P” designates a stop condition and PEC a packet error code. White parts designate a communication from a master to slave, gray parts a slave-to-master communication. Three dots designate a continuation of protocol. 
       FIG. 2  shows a quick command protocol. Here the R/W bit denotes the command which may be used to simply turn a device function on or off. 
       FIGS. 3 and 4  show a sent byte protocol wherein the protocol of  FIG. 4  comprises a PEC byte. The data byte transferred to the slave device may designate up to 256 possible encoded commands. 
       FIG. 5  shows a receive byte protocol.  FIG. 6  shows a receive byte protocol with PEC. The receive byte protocol is similar to a send byte protocol. The only difference is the direction of data transferred. A NACK (a “1” in the ACK bit position) signifies the end of a transfer. 
       FIG. 7  shows a write byte protocol,  FIG. 8  a write word protocol,  FIG. 9  a write byte protocol with PEC and  FIG. 10  a write word protocol with PEC. The first byte of a write byte/word protocol is the command code. The next one or two bytes, respectively, are the data to be written. In this example, the master inserts the slave devise address followed by the write bit. The slave device acknowledges and the master delivers the command code. This slave again acknowledges before the master sends the data byte or word. The slave acknowledges each byte and the entire transaction is finished with a STOP condition. 
       FIGS. 11 ,  12 ,  13  and  14  show a read byte protocol, a read byte protocol with PEC, a read word protocol and a read word protocol with PEC, respectively. When reading data, the master must write a command to the slave device. Then it must follow that command with a repeated start condition to denote a read from that device&#39;s address. The slave then returns one or two bytes of data. There is no STOP condition before the Repeated START condition. A NACK signifies the end of the read transfer protocols. 
       FIG. 15  illustrates a process call protocol.  FIG. 16  presents a process call protocol with PEC. The process call protocol is so named because a command sends data and waits for the slave to return a value dependent on that data. The protocol is simply a write word followed by read word without the read word command field and the write-word STOP bit. 
       FIG. 17  shows a block write protocol.  FIG. 18  illustrates a block write protocol with PEC. The block write protocol begins with a slave address and a write condition. After the command code, the master issues a byte count which describes how many more bytes will follow the message. If a master has 20 bytes to send, the byte count field will have a value of 20 (14h), followed by the 20 bytes of data. The byte count does not include the PEC byte and may not be zero. A block write protocol is allowed to transfer a maximum of 32 data bytes. 
       FIG. 19  shows a block read protocol and  FIG. 20  a block read protocol with PEC. A block read differs from a block write in that the repeated START condition exists to satisfy the requirement of a change in the transfer direction. A NACK immediately preceding the STOP condition signifies the end of the read transfer. Also, a block read protocol is allowed to transfer a maximum of 32 data bytes. 
       FIG. 21  shows a block write-block read process call protocol whereas  FIG. 22  shows such a protocol including a PEC. The block write-block read process call is a two-part message. It begins with the slave address and a write condition. After the command code, the host issues a write byte count that describes how many more bytes will be written in the first part of the message. The second part of the message is a block of read data beginning with a repeated START condition followed by the slave address and a read bit. The next byte is the read byte count which may differ from the write byte count. Both the write byte count and the read byte count cannot be zero. The sum of the write byte count and the read byte count must not exceed 32 bytes. The read byte count does not include the PEC byte. 
     A standard interface for controlling an SMBus is defined in Advanced Configuration and Power Interface (ACPI), Specification 2.0. Via that interface described in Section 13.9 of the ACPI Specification, an ACPI-compatible operating system can communicate with embedded controller-based SMBus host controllers (EC-SMB-HG). The interface consists of a block of registers that reside in embedded controller address space. These registers are used by software to initiate SMBus transactions and receive SMBus notifications.  FIG. 23 , reference numeral  208 , designates an ACPI-compliant register set. 
     The protocol register designated SMB_PRTCL determines the type of SMBus transaction generated on the SMBus. A write to this register initiates a transaction on the SMBus. If the most significant bit (MSB) of this register is set to one (1), a PEC format should be used for the specified protocol, and a value of zero indicates the standard format without PEC should be used. The following table 1 maps the protocol values to the protocol. An “h” following a number indicates that the number is a hexadecimal number throughout this specification. 
     
       
         
               
               
               
             
           
               
                   
                 TABLE 1 
               
               
                   
                   
               
             
             
               
                   
                 00h 
                 CONTROLLER NOT IN USE 
               
               
                   
                 01h 
                 RESERVED 
               
               
                   
                 02h 
                 WRITE QUICK COMMAND 
               
               
                   
                 03h 
                 READ QUICK COMMAND 
               
               
                   
                 04h 
                 SEND BYTE 
               
               
                   
                 05h 
                 RECEIVE BYTE 
               
               
                   
                 06h 
                 WRITE BYTE 
               
               
                   
                 07h 
                 READ BYTE 
               
               
                   
                 08h 
                 WRITE WORD 
               
               
                   
                 09h 
                 READ WORD 
               
               
                   
                 0Ah 
                 WRITE BLOCK 
               
               
                   
                 0Bh 
                 READ BLOCK 
               
               
                   
                 0Ch 
                 PROCESS CALL 
               
               
                   
                 0Dh 
                 BLOCK WRITE-BLOCK READ 
               
               
                   
                   
                 PROCESS CALL 
               
               
                   
                   
               
             
          
         
       
     
     The status register designated SMB_STS indicates general status on the SMBus. This register is cleared to zero, except for the alarm bit whenever a new command is issued using a write to the protocol register. This register is always written with the error code before clearing the protocol register. 
     The address register designated SMB_ADDR contains the 7-bit address to be generated on the SMBus in the seven most significant bits (MSB). The least significant bit (LSB) is reserved. The command register designated SMB_CMD contains the command byte that will be sent to the target devise on the SMBus. The register set further comprises 32 data registers designated SMB_DATA[i], i=0-31. The data registers contain the remaining bytes to be sent or received in any of the different protocols that can be run on the SMBus. The block count register designated SMB_BCNT contains the number of bytes of data present in the data registers SMB_DATA[i]. Moreover, the ACPI-compliant register set comprises three alarm registers designated SMB_ALRM_ADDR, SMB_ALRM_DATA[0] and SMB_ALRM_DATA[1]. 
     The location of each register is defined by an offset to be added to a base address, as shown in  FIG. 23  in column  209  left of the ACPI-compliant register set  208 . The address of the protocol register is equivalent to the base address. 
     Although a specification for an SMBus and a specification for a register set for ACPI-compatible operating systems has been published, it is desirable to provide a memory-efficient SMBus message handler, an integrated circuit chip and a respective method. Moreover, it is desirable to provide an SMBus test device for verifying the chip sets and a respective method. 
     SUMMARY OF THE INVENTION 
     According to one embodiment, an SMBus message handler comprises a memory for storing microcode which comprises at least two programs, each for handling a bus command protocol and comprising at least one instruction. The SMBus message handler further comprises an interface to a register for identifying a starting address of a program in the memory. An instruction fetch unit comprised in the SMBus message handler reads an instruction at an address in the memory. The address is specified by a program counter. Finally, the SMBus message handler comprises a finite-state machine which receives and interprets the instructions from the instruction fetch unit and manages the data transfer between an SMBus interface and a register set in compliance with the instructions read from the memory. 
     According to another embodiment, an integrated circuit chip for transmitting and receiving data over an SMBus comprises an interface to a memory which stores microcode which comprises at least two programs, each for handling a bus command protocol and comprising at least one instruction. The chip may be connected via an interface to a register for identifying a starting address of a program in the memory. Further, the chip comprises an instruction fetch unit for reading an instruction at an address in the memory which is specified by a program counter. Finally, the chip comprises a finite-state machine for receiving and interpreting the instructions and for managing the data transfer between an SMBus interface and a register set in compliance with the instructions read from the memory. 
     According to yet another embodiment, a method for controlling an SMBus comprises identifying a starting address of a program which comprises at least one instruction. The program is stored in a memory. The method further comprises fetching instructions of said program one after another into a finite-state machine. Finally, according to the method, data are transferred between an SMBus interface and a register set in compliance with the instructions present in the finite-state machine. 
     According to a further embodiment, an SMBus test device comprises a memory in which sequences of instructions are stored. The SMBus test device further comprises an SMBus interface to which a plurality of SMBus devices can be connected and an interface for inputting keys. Finally, a processor in the SMBus test device checks as to whether a key is input via the respective interface. Upon inputting of a key, the processor further checks as to whether said key can be mapped to a sequence of instructions for controlling devices connected to said SMBus interface or transferring data to or receiving data from said devices connected to said SMBus. Finally, the processor executes the sequence of instructions to which the key has been mapped. 
     According to yet a further embodiment, a method for controlling a testing system for SMBus chip set validation comprises checking as to whether a key is input from a second interface. Upon inputting of a key checking as to whether the key can be mapped to any sequence of instructions for controlling devices connected to an SMBus or transferring data to or receiving data from the devices connected to the SMBus. Finally, according to the method, the sequence of instructions to which said key has been mapped is executed. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Further embodiments, advantages and objects of the present invention are defined in the appended claims and will become more apparent with the following detailed description when taken with reference to the accompanying drawings in which 
         FIG. 1  shows a generic SMBus packet protocol diagram; 
         FIG. 2  shows a quick command protocol; 
         FIG. 3  shows a send byte protocol; 
         FIG. 4  shows a send byte protocol with PEC; 
         FIG. 5  shows a receive byte protocol; 
         FIG. 6  shows a receive byte protocol with PEC; 
         FIG. 7  shows a write byte protocol; 
         FIG. 8  shows a write word protocol; 
         FIG. 9  shows a write byte protocol with PEC; 
         FIG. 10  shows a write word protocol with PEC; 
         FIG. 11  shows a read byte protocol; 
         FIG. 12  shows a read byte protocol with PEC; 
         FIG. 13  shows a read word protocol; 
         FIG. 14  shows a read word protocol with PEC; 
         FIG. 15  shows a process call protocol; 
         FIG. 16  shows a process call protocol with PEC; 
         FIG. 17  shows a block write protocol; 
         FIG. 18  shows a block write protocol with PEC; 
         FIG. 19  shows a block read protocol; 
         FIG. 20  shows a block read protocol with PEC; 
         FIG. 21  shows a block write-block read process call protocol; 
         FIG. 22  shows a block write-block read process call protocol with PEC; 
         FIG. 23  shows a block diagram of an SMBus host controller; 
         FIG. 24  shows the bits of a status register; 
         FIG. 25  shows a sixbit instruction for the finite-state machine; 
         FIG. 26  shows a block diagram of a master finite-state machine; 
         FIG. 27  shows an overview of a test device; 
         FIGS. 28 to 32  show flow diagrams for mapping keys to instruction sets; 
         FIG. 33  shows a flow chart for modifying a single byte in the auxiliary RAM of the embedded controller; 
         FIG. 34  shows a flow chart for controlling the sending of wrong acknowledgments or non-acknowledgments; 
         FIG. 35  shows a flow chart for inputting an offset to PEC; 
         FIG. 36  shows a flow diagram for inputting timeout error settings; and 
         FIG. 37  shows a flow diagram for inputting a new device address. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     While the present invention is described with reference to the embodiments as illustrated in the following detailed description, as well as in the drawings, it should be understood that the following detailed description as well as the drawings are not intended to limit the present invention to the particular illustrative embodiment disclosed, but rather the described illustrative embodiments merely exemplify the various aspects of the present invention, the scope of which is defined by the appended claims. 
     As previously explained, an SMBus message handler comprises a finite-state machine which receives and interprets instructions stored in a memory and manages the data transfer between an SMBus interface and a register set in compliance with the instructions read from the memory. Moreover, this finite-state machine may be integrated into a circuit chip. 
     Moreover, an SMBus test device comprise an SMBus interface, a keyboard and a processor for mapping input keys to sequences of instructions. The instructions are executed and respective commands or data are sent or received via the SMBus interface. 
       FIG. 23  shows a block diagram of an SMBus host controller  200 . As explained above, the host controller comprises an ACPI-compliant register set  208 . The memory address  209  of each register is specified by an offset of 0 to 40 to be added to a base address Base of the first register SMB_PRTCL. The host controller further comprises an address register array  207 , a ROM  202  which stores several microcode sequences  210 ,  211  and  212 , each comprising one or more instructions. The host controller comprises in addition a loop counter  204 , an instruction fetch unit  203 , including a program counter (designated “pc” in the box shown within instruction fetch unit  203 ), a finite-state machine  201 , a buffer pointer  206 , a PEC unit  215 , and an SMBus interface comprising a clock line SMBCLK  213  and a data line SMBDAT  214 . 
     As explained above, in compliance with the ACPI-embedded controller interface specification, an SMBus transaction is initiated by a write to the protocol register SMB_PRTCL. The value written may range from 01h to 0Dh excluding the most significant bit which specifies as to whether a PEC format or a non-PEC format should be used in hexadecimal format, indicated by the post-positioned “h”. The seven least significant bits (LSBs) of the protocol register are used as a pointer to a cell within the address register array  207 . The address register array  207 , in turn, comprises pointers to each start of a microcode sequence which is illustrated by the dashed arrows from the address register array entries to the microcode sequences  210 ,  211 ,  212 . 
     After a write to the protocol register, the value of the corresponding address register array cell is transferred to the program counter pc within the instruction fetch unit  203 . The most significant bit of the protocol register is also fed into the finite-state machine (FSM)  201 . Depending on the value of the MSB of the protocol register, the finite-state machine may use a PEC format or a non-PEC format protocol. 
     In an alternate embodiment two address register arrays may be provided. The first one comprises the starting address for microcode sequences for non-PEC format protocols whereas the second address register array comprises pointers to microcode sequences for PEC format protocols. 
     A buffer pointer register  206  comprises the offset value of one of the data registers SMB_DATA[ . . . ]. After a write to or read from one of the data registers, the buffer pointer register  206  bufp, is incremented by one so that the next read or write is performed to or from the next data register. That is providing or reading of data to one of the data registers SMB_DATA[bufp]. Additional connections between the individual registers of the register set  208  and the finite-state machines are provided so that the finite-state machine  201  can read or write to any register of the register set  208 . In addition to the registers provided by the ACPI specification, an additional register SMB_SLAVE_ADDR for the slave address is provided at an offset of 40 with respect to the base address of the register set. 
     An implementation of the instructions used for the microcode sequences is shown in  FIG. 25 . Table 3 comprises microcode sequences for non-PEC formats. The three least significant bits (LSB)  300 ,  301 ,  302  specify the register from which data are transferred to the SMBus interface  213 ,  214  or to which data received from the SMBus interface are written to. Table 2 illustrates the meanings of bits  300 ,  301 ,  302 . 
     
       
         
               
               
             
           
               
                 TABLE 2 
               
               
                   
               
             
             
               
                 0 
                 None 
               
               
                 1 
                 Transmit data from SMB_ADDR with a bit 
               
               
                   
                 value of 1 at the R/W bit position 
               
               
                 2 
                 Transmit data from SMB_ADDR with a bit 
               
               
                   
                 Value of 0 at the R/W bit position 
               
               
                 3 
                 Transmit data from SMB_CMD 
               
               
                 4 
                 Transmit data from SMB_BCNT, set 
               
               
                   
                 loopcnt = SMB_BCNT 
               
               
                 5 
                 Transmit data from SMB_DATA[bufp], 
               
               
                   
                 increment bufp 
               
               
                 6 
                 Receive data to SMB_DATA[bufp], 
               
               
                   
                 increment bufp 
               
               
                 7 
                 Receive data to SMB_BCNT, set 
               
               
                   
                 loopcnt = SMB_BCNT 
               
               
                   
               
             
          
         
       
     
     If Bit  3  is 1, a repeated START condition will be generated on the SMBus interface. If, on the other hand, the latter bit is zero, no repeated START condition will be generated. 
     If the value of Stop Bit  4   304  is 1 and the host controller acts as a transmitter, a STOP condition will be generated upon receiving ACK If the SMBus host controller is in receiver mode, NACK and a STOP condition is generated. If Bit  4  is zero, no STOP condition will be generated. If Bit  4  of an instruction has a value of 1, this means that this instruction is the last instruction in a microcode sequence. After that instruction, the protocol register SMB_PRTCL is set to zero. 
     If the most significant Loop Bit  5   305  has a value of zero, an instruction is only executed once. That means that after the execution the program counter pc within the instruction fetch unit  203  is incremented by one and the next instruction is fetched. If bit  5  has a value of 1, the instruction remains in the finite-state machine  201  until the loop counter  204  becomes zero. Each time the instruction is executed, the loop counter loopcnt is decremented by one. For each START or repeated START condition, the loop counter is set to one for non-I 2 C transactions or set to SMB_BCNT for I 2 C transactions. Moreover, whenever an access to the SMB_BCNT register occurred, loop counter  204  is set to SMB_BCNT. 
     Whenever a START or repeated START condition is generated, the buffer pointer register  206  bufp is set to 04h, which is the offset of the data register SMB_DATA[0]. Whenever an access to the data register, i.e. reading or writing, occurred, the buffer pointer register will be incremented. 
     
       
         
               
               
               
               
               
               
             
           
               
                 TABLE 3 
               
               
                   
               
               
                   
                   
                   
                 Microcode 
                   
                   
               
               
                 SMB_PRTCL 
                 Command 
                 ROM-Address 
                 (binary) 
                 Start 
                 Remarks 
               
               
                   
               
             
             
               
                 02h 
                 Write Quick 
                 0h 
                 01_0010 
                 S 
                 bufp = 4; loopcnt = 2 
               
               
                 03h 
                 Read Quick 
                 1h 
                 01_0001 
                 S 
                 bufp = 4; loopcnt = 2 
               
               
                 04h 
                 Send Byte 
                 2h 
                 00_0001 
                 S 
                 bufp = 4; loopcnt = 2 
               
               
                   
                   
                 3h 
                 01_0011 
               
               
                 05h 
                 Receive 
                 4h 
                 00_0001 
                 S 
                 bufp = 4; loopcnt = 2 
               
               
                   
                 Byte 
                 5h 
                 01_0110 
               
               
                 06h 
                 Write Byte 
                 6h 
                 00_0010 
                 S 
                 bufp = 4; loopcnt = 2 
               
               
                   
                   
                 7h 
                 00_0011 
               
               
                   
                   
                 8h 
                 01_0101 
               
               
                 07h 
                 Read Byte 
                 9h 
                 00_0010 
                 S 
                 bufp = 4; loopcnt = 2 
               
               
                   
                   
                 Ah 
                 00_0011 
               
               
                   
                   
                 Bh 
                 00_1001 
                 Sr 
                 bufp = 4; loopcnt = 2 
               
               
                   
                   
                 Ch 
                 00_0110 
               
               
                 08h 
                 Write Word 
                 Dh 
                 00_0010 
                 S 
                 bufp = 4; loopcnt = 2 
               
               
                   
                   
                 Eh 
                 00_0011 
               
               
                   
                   
                 Fh 
                 11_0101 
               
               
                 09h 
                 Read Word 
                 10h 
                 00_0010 
                 S 
                 bufp = 4; loopcnt = 2 
               
               
                   
                   
                 11h 
                 00_0011 
               
               
                   
                   
                 12h 
                 00_1001 
                 Sr 
                 bufp = 4; loopcnt = 2 
               
               
                   
                   
                 13h 
                 11_0110 
               
               
                 0Ah 
                 Write Block 
                 14h 
                 00_0010 
                 S 
                 bufp = 4; loopcnt = 2 
               
               
                   
                   
                 15h 
                 00_0011 
               
               
                   
                   
                 16h 
                 00_0100 
                   
                 loopcnt = SMB_BCNT 
               
               
                   
                   
                 17h 
                 11_0101 
               
               
                 0Bh 
                 Read Block 
                 18h 
                 00_0010 
                 S 
                 bufp = 4; loopcnt = 2 
               
               
                   
                   
                 19h 
                 00_0011 
               
               
                   
                   
                 1Ah 
                 00_1001 
                 Sr 
                 bufp = 4; loopcnt = 2 
               
               
                   
                   
                 1Bh 
                 00_0111 
                   
                 loopcnt = SMB_BCNT 
               
               
                   
                   
                 1Ch 
                 11_0110 
               
               
                 0Ch 
                 Process Call 
                 1Dh 
                 00_0010 
                 S 
                 bufp = 4; loopcnt = 2 
               
               
                   
                   
                 1Eh 
                 00_0011 
               
               
                   
                   
                 1Fh 
                 10_0101 
               
               
                   
                   
                 20h 
                 00_1001 
                 Sr 
                 bufp = 4; loopcnt = 2 
               
               
                   
                   
                 21h 
                 11_0110 
               
               
                 0Dh 
                 Block Write- 
                 22h 
                 00_0010 
                 S 
                 bufp = 4; loopcnt = 2 
               
               
                   
                 Block Read 
                 23h 
                 00_0011 
               
               
                   
                 Process Call 
                 24h 
                 00_0100 
                   
                 loopcnt = SMB_BCNT 
               
               
                   
                   
                 25h 
                 10_0101 
               
               
                   
                   
                 26h 
                 00_1001 
                 Sr 
                 bufp = 4; loopcnt = 2 
               
               
                   
                   
                 27H 
                 00_0111 
                   
                 loopcnt = SMB_BCNT 
               
               
                   
                   
                 28h 
                 11_0110 
               
               
                 4Ah 
                 Block Write 
                 29h 
                 00_0010 
                 S 
                 bufp = 4; loopcnt = SMB_BCNT 
               
               
                   
                 12C 
                 2Ah 
                 00_0011 
               
               
                   
                   
                 2Bh 
                 11_0101 
               
               
                 4Bh 
                 Block Read 
                 2Ch 
                 00_0010 
                 S 
                 bufp = 4; loopcnt = SMB_BCNT 
               
               
                   
                 12C 
                 2Dh 
                 00_0011 
               
               
                   
                   
                 2Eh 
                 00_1001 
                 Sr 
                 bufp = 4 
               
               
                   
                   
                 2Fh 
                 11_0110 
               
               
                   
               
             
          
         
       
     
     The left column of Table 3 comprises the value of the seven least significant bits of the protocol register SMB_PRTCL. The second column comprises the name of the protocol. The third column comprises the hexadecimal address in ROM  202 . The fourth column comprises the 6-bit binary microcode instructions. An “S” in the fifth column designates a START condition, whereas an “Sr” in this column designates a repeated START condition. The right column illustrates the values to which the buffer pointer register bufp  206  and the loop counter  204  are set. Skilled practitioners will appreciate that an additional bit may be added for reads or writes to the PEC unit  215  and how the microcode sequences may be supplemented in order to handle the PEC formats of the SMBus protocols. 
       FIG. 26  shows a flow chart  400 , which illustrates the operation of a master finite-state machine  201 . Usually the finite-state machine is in idle mode  401 . After a write to the protocol register, the address of the first instruction of the microcode is obtained from the address register array and the first instruction of the microcode sequence is loaded in step  402 . In step  403  it is determined whether data are to be received from the SMBus interface or data are to be transmitted to the SMBus interface. If data are to be transmitted, it is further checked as to whether a repeated START condition is to be generated in step  404 , and if that is the case, the repeated START condition is prepared in step  406 . If no repeated START condition is to be generated, it is checked in step  405  as to whether a START condition is to be generated, and if that is the case, the START condition is generated in step  407 . If a repeated START condition has been prepared in step  406 , also a START condition is generated in step  407 . 
     Then, in step  408 , the data from the respective register of the ACPI-compliant register set  208  are loaded. In step  409 , a byte of data is sent to the SMBus interface. In step  411 , it is decided as to whether in step  410  an ACK has been received. If no ACK was received, the protocol is aborted in step  417  and a STOP is generated in step  430 . 
     If an acknowledgment has been received in step  411 , it is checked in step  412  as to whether Bit  5 ,  305  has a value of one. If this is the case, it is determined in step  413  as to whether the loop counter loopcnt  204  is equivalent to zero. If this is not the case, loopcnt is decremented by one in step  414 , and the next loading of a data byte in step  408  takes place from a register of the ACPI-compliant register set. 
     If either Bit  5 ,  305  has a value of zero or loopcnt is equivalent to zero, it is determined in step  415  as to whether Stop Bit  4 ,  304  is set. If this is the case, it is checked in step  416  as to whether a PEC format is to be used. If the Stop Bit  4  has a value of zero the follow proceeds from step  415  to step  402  i.e. the next instruction is loaded from memory  202 . If it is decided in step  416  that a PEC format is to be used then the PEC data byte is loaded in step  408 . If a non-PEC format is to be used, a stop condition is generated in step  430 . 
     If it is decided in step  403  that data are to be received from the SMBus interface the flow proceeds to step  420  in which a data byte is received from the SMBus interface. This data byte is saved to one of the registers of the ACPI-compliant register set in step  421 . 
     Steps  422  to  426  are similar to steps  412  to  416 , respectively. However, after it is decided in step  426  that a non-PEC format is to be used, a NACK is sent in step  427  after step  426 . If it is determined in step  423  that the loop counter loopcnt is not zero or it is determined in step  425  that the Stop Bit  4 ,  304  has a value of zero or it is determined that a PEC format is to be used in step  426 , an ACK is sent in step  428 . Then it is decided in step  429  as to whether Stop Bit  4 ,  304  is set or not. If it has a value of one then the flow proceeds to step  420  in which the next data byte is received from the SMBus interface. If the Stop Bit  4  has a value of 0, the flow proceeds to step  402  in which the next instruction is loaded from memory  202 . 
       FIG. 27  shows a test hardware  500  for chip set validation. It comprises a SMBus connector  520 , an SMBus host  501 , rapid development boards  521 ,  522  and  523 . The SMBus host  501  comprises a personal computer (PC) including a screen  502 , a casing  503  including a processor memory and a keyboard  504 . The SMBus interfaces  505  of the SMBus host  501  and the rapid development boards  521  to  523  are connected to the SMBus connector  520 . The SMBus connector connects the clock lines SMBCLK and the data lines SMBDAT and the optional alert line SMBALERT# of each of the SMBus interfaces. In addition, pull-up resistors of  10  (are provided in the SMBus connector  520  in compliance with the SMBus specification, section  2 . 
     The rapid development boards are provided in addition to the SMBus interface with an RS-232 interface via which the rapid development boards can be connected to another terminal  511  which may be PC having a display  512  and a keyboard  514 . In one embodiment phyCORE-591 may be used for the rapid development boards. phyCORE-591 can be ordered from PHYTEC. This board is equipped with a Philips Processor 8xC591 which implements the I 2 C hardware which is used to test the capabilities of the SMBus host. A software may be run on terminal  511  which forwards every key input into terminal  511  by keyboard  514  via the RS-232 interface to one of the rapid development boards. The software may further display any character or byte received by the RS-232 interface on display  512 . In addition, not only or alternatively do the bytes received by the RS-232 interface an explanation may be shown on display  212 . Further, the software may provide different options so that different categories of bytes received by the RS-232 interface may be displayed or not displayed. 
       FIG. 28 to 23  show a flow-chart illustrating the operation of the user interface of the SMBus test equipment. The steps shown in  FIGS. 28 to 32  may be performed by the processor of the SMBus host if the keys are input into keyboard  504 . In another embodiment the steps of  FIGS. 28 to 32  may be performed by the processor of the rapid development board if the depressing of keys on keyboard  514  is echoed on the RS-232 interface. 
     Usually, the test device is in idle state  601 . If it is determined in step  602  that a key is pressed it is determined in steps  603 ,  605 ,  608 ,  610 ,  613 ,  615 ,  617 ,  619 ,  622 ,  624 ,  627 ,  629 ,  632 ,  634 ,  637 ,  639 ,  641 ,  643 ,  645 ,  647 ,  649 ,  651 ,  653 ,  655  and  657  which key is depressed and as to whether an instruction is associated with that key. 
     If it is determined in step  603  that a “0” was input an block write according to the I 2 C specification is executed in step  604 . That means the data as indicated in the lower line of block  604  in hexadecimal format are written to the SMBus interface. A “v” at the end of the data is short for an ACK. The slave device will receive incoming data till the recognition of a stop condition. If it is determined in step  601  that a “1” was input an I 2 C command block read is executed. That means that the test device will transmit data bytes from its auxiliary RAM starting at offset zero until the recognition of a NACK transmitted by the master. The lower line of block  606  indicates the data which may be transmitted from the slave device to the test device in hexadecimal format. The “v” at the end of the data stream indicates an ACK. Then in step  607  PEC is turned on or off which means that a non-PEC format is chosen if a PEC format has been chosen up to now or vice versa. 
     If “2” is input, what is determined in step  608 , a quick write is executed in step  609  that means that the data byte AEh is transmitted by the master and the slave device acknowledges its own address. If “3” is input, determined in step  610 , a quick read is performed in step  611  which means that the data byte AFh is transmitted from the master and the slave acknowledges its own address. Then in step  612  PEC is turned on or off. 
     If it is determined in step  613  that “4” is input a send-byte command is executed in step  614  which means that the data in lines  2  or  3  are transmitted by the master depending as to whether a non-PEC or PEC format is chosen. If it is determined in step  615  that “5” is input, a receive byte protocol is executed in step  616 . The test device receives the first data byte of the auxiliary RAM of a slave device. That means depending on the format, the bytes indicated in the 2 nd  or 3 rd  lines of block  616  are transmitted via the SMBus. Then, as indicated in step  670  the PEC is turned on or off. 
     If it is determined in step  617  that a “6” is input, a write byte command is executed as shown in block  618 . If “7” is input, a read byte protocol is executed in step  620  as always, the data which may be transferred over the SMBus are indicated in lines  2  or  3  of block  620 . Then in step  621  the PEC is turned on or off. 
     If “8” is input, which is determined in step  622 , a write word command is executed in step  623 . If “9” is pressed (step  624 ), a read word command is executed in step  625  and the PEC is turned on or off in step  626 . 
     If it is determined in step  627  that an “A” is input, a write block protocol is executed in step  628 . If “B” is input (step  629 ), a read block protocol is executed in step  630  and subsequently in step  631  the PEC is turned on or off (step  634 ). If a “C” is input (step  632 ), a process call protocol is performed in step  633 . If a “D” is input (step  634 ), a block write-block read process call is executed in step  635  and the PEC is turned on or off in step  636 . If an “E” is input (step  637 ), the host is notified of an alarm in step  638 . That is performed by the data sequence of line  2  of block  638  in hexadecimal format. 10h is the host notify address, AEh is the own address and 00h 01h are two data bytes. 
     The transmission of a remote control message is started by pushing “F” which is determined in step  639 . The message is basically in a write byte protocol the data transmitted depends on the currently selected remote control device address and status which may be changed by pressing “G” which is determined in step  657 . The following table 4 illustrates the remote control status codes and the data transmitted. 
     
       
         
               
               
               
               
             
           
               
                   
                 TABLE 4 
               
               
                   
                   
               
               
                   
                 Status 
                 Command code 
                 Data byte 
               
               
                   
                   
               
             
             
               
                   
                 power cycle 
                 03h 
                 82h 
               
               
                   
                 power down 
                 02h 
                 6Eh 
               
               
                   
                 power up 
                 01h 
                 65h 
               
               
                   
                 Reset 
                 00h 
                 52h 
               
               
                   
                 send random data 
                 ??h 
                 ??h 
               
               
                   
                   
               
             
          
         
       
     
     A change of the slave address may be initiated by pressing “S” which is determined in step  641 . Then in step  642  a two digit hexadecimal number may be input as illustrated e.g. in  FIG. 35  in connection with inputting of an offset to the PEC. 
     When a “P” is input which is checked in step  643 , the PEC is turned on or off in step  644 . The verbose mode may be turned on or off by pressing a “V” in step  645 . If the verbose mode is turned on in steps  646  which is by the way the default case then every single byte of a SMBus message will be echoed on screen  502  or transmitted via the RS-232 interface to terminal  512 . 
     Entering a “M” which is determined in step  647 , lets the user modify a single byte in the auxiliary RAM in the imbedded controller which is used to store outgoing message data. Step  648  is illustrated in greater detail in  FIG. 33 . An acknowledgment error feature may be turned on by pressing “N” which is determined in step  649 . Then an ACK or NACK error position may be specified in step  650  which will be explained in more detail in connection with  FIG. 34 . When “O” is pressed which is determined in steps  641 , an offset to PEC may be input in step  652  which is explained in more detail in connection with  FIG. 35 . When “T” is input which is determined in step  653  time out error settings may be input in step  654  which is illustrated in more detail in connection with  FIG. 36 . Pressing “R” which is determined in step  655  turns an arbitration error on or off (step  656 ). 
     Pressing “G” which is determined in step  657  lets the user change the remote control settings. After step  657  the test device waits in step  658  for the input of another key. It is checked in steps  659 ,  661 ,  663 ,  665 ,  667  and  669  as to whether an action is associated with the key inputted. 
     If the key is “0”, the status is re-set in step  660  i.e. a write byte protocol is executed wherein a 00h command code and 52h data byte (confer table 4) is sent. 
     If “1” is input, which is determined in step  661 , a power down status is set in step  662 . The bytes sent in the write byte protocol are displayed in line  2  (excluding the headline row) of table 4. 
     If “2” is input, which is determined in step  663 , a power up status is set in step  664  (confer line  3  of table 4). If “3” is input, as checked out in step  665 , a power cycle status is set in step  666  (confer line  1  of table 4) If, “4” is input, (step  667 ), random data are sent in step  668 . If it is found out that an “A” is input in step  669  the device address may be changed in step  671  as will be explained in more detail in connection with  FIG. 37 . 
       FIG. 33  illustrates the modify byte operation in step  648 . The test equipment waits in step  701  for the input of a key. Then it is checked in step  702  as to whether the key is hexadecimal key. A hexadecimal key is either a number between 0 and 9 or a character between A and F. If a hexadecimal key is input, its value is saved as a 1  for later use in step  704 . If a non-hexadecimal key is input, the flow proceeds to step  703  where it is determined as to whether return is input. If that is the case, the flow proceeds to the end in steps  718 . If it is determined in step  703  that a key different from the return keys input, the test equipment waits in step  701  for the input of another key. 
     Steps  705  to  708 ,  709  to  712  and  713  to  716  are similar to steps  701  to  704 . However, the key input in step  705  is saved as a 2  for later use, the key input in step  709  is saved as v 1  for later use in step  712  and the key input in step  713  is saved for later use in step  716  as v 2 . Finally in  717  a single byte in the auxiliary RAM of the embedded controller is changed which is used to store outgoing message data. a 1  constitutes the 4 MSBs and a 2  the 4 LSBs of the hexadecimal address in the RAM and v 1  v 2  the 4 MSBs and the 4 LSBs, respectively, of the value itself. If instead of a hexadecimal key return is pressed the flow doesn&#39;t proceed to step  717  so the original value is maintained. 
       FIG. 34  illustrates step  650  in which a ACK or NACK position may be specified. Steps  721  to  724  and steps  725  to  728  are similar to steps  701  to  704  in  FIG. 33 . However, it is checked in step  722  and  726  as to whether a numeric key, that is a number between 0 and 9 is input. The first number input in step  721  and saved in step  724  for later use as “z”, which will form the tens and the second number input in step  725  and saved for later use in step  728  as “e” forms the ones of the byte location for the error. The byte location for the error is saved in step  729 . 
       FIG. 35  illustrates step  652  for inputting an offset to the PEC. The whole procedure is similar to the one shown in  FIG. 34 . However, this procedure accepts hexadecimal keys in step  742  and  746 . The key input in step  741  constitute the four most significant bits whereas the key input in step  745  constitutes for least significant bits of the offset to be added to the PEC byte ( 749 ). 
       FIG. 36  illustrates step  654  for inputting the time-out error settings. This procedure is similar to the one shown in  FIG. 33 . However, step  762 ,  766 ,  770  and  774  accept numeric keys only. The first number input and saved as I 1  in step  764  will form the tens whereas the second number saved in step  768  for later use as I 2  will form the ones of the error location (step  777 ). The third numeric key saved as t 1  in step  772  will form the tens and the fourth numeric key t 2  will form the ones of the time-out time. If the time-out error is turned on by pushing T the SMBCLK line will be pulled down for a given time, while the host is waiting for the acknowledge of the last byte. 
       FIG. 37  illustrates the change of a device address in step  671 . This flow-chart is similar to the flow-chart shown in  FIG. 35 . The first hexadecimal key a 1  inputted will form the four most significant bits of the new device address, whereas the second hexadecimal will key a 2  the four least significant bits of the new device address which is stored in step  790 . If return instead of a hexadecimal is pressed, no change takes place. 
     In a further embodiment, the command as indicated in the first line of step  604 ,  606 ,  609 ,  611 ,  614 ,  616 ,  618 ,  620 ,  623 ,  625  and  628  may be echoed on the RS-232 interface and then be displayed on screen  512  of terminal  511 . Furthermore, the data bytes send and received by the SMBus as indicated in the 2 nd  and 3 rd  lines of the above-identified blocks, may be echoed on the RS-232 interface and also be displayed on the screen  512 . Also the SMBus host  501  may display the commands and/or the data bytes sent by the SMBus on its display. 
     Further modifications and variations of the present invention will be apparent to those skilled in the art in view of this description. Accordingly, this description is to be construed as illustrative as only and is for the purpose of teaching those skilled in the art the general manner of carrying out the present invention.