Abstract:
A control method of synchronizing operation frequencies of a CPU and a system RAM in a power management process. A power management process is initialized by a system interrupt generated by a power management event. After sending the interrupt control signal output from the chipset to the CPU, the CPU enters a system management mode to execute an interrupt service routine. The interrupt service routine irrelevant to the system RAM configuration is executed first. The shadow RAM control register of the chipset is programmed using the BIOS program to enable the BIOS ROM. A distant jump command is programmed to jump into a predetermined memory address of the BIOS ROM storing a system RAM frequency modulation program to execute the system RAM frequency program. Therefore, the operation frequencies of the CPU and the system RAM are consistent during the power management process to eliminate the instability of system caused thereby.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the priority benefit of Taiwan application serial no. 90120584, filed Aug. 22, 2001. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates in general to a power management process in an advanced configuration power interface (ACPI) computer system, and more particularly, to a method of increasing system execution stability of the power management process by synchronizing the operation frequencies of system random access memory (RAM) and the central processing unit (CPU) while a executing power management process in the system management mode (SMM). 
     2. Description of the Related Art 
     Power management techniques such as the advance power management (APM) have been broadly applied to personal computers. For the current computer system, most of the system basic input/output systems (BIOS) and process systems provide functions to support power management. The power management process is performed via the BIOS program stored in the system read only memory (ROM). When a power management event or a power configuration event (such as a request to convert a “work” state into a “sleep” state) occurs to the legacy OS system, an interrupt of OS-transparent is generated to the power management event or power configuration. This is called system management interrupt (SMI). The BIOS receives the notice of interrupt event via the system management interrupt. While the event occurs, the BIOS communicates with the operating system to generate a system management interrupt to the CPU after the operating system acknowledges all the OS level device drivers, so as to transfer control to the system BIOS. The system BIOS is responsible for processing the required software state information and controlling the related hardware to complete the request. When the system wakes up by a wake-up event, the BIOS again receives notice from a system management interrupt. All the required resume operations of the hardware state information are executed before returning control to the operating system. 
     In the later ACPI computer system, when a power management event or a power state event occurs, an interrupt which has to be shareable and OS-visible is generally generated. This interrupt is called the system control interrupt (SCI). The operating system guides a power state change for the entire system and apparatus. Nowadays, the ACPI has become the key device for operating system directed configuration and power management (OSPM). 
     The ACPI comprises several listings, a BIOS and a hardware register. The ACPI listings (definition blocks) are used to describe the system state information and the control method. The ACPI BIOS is a part of the system firmware that completes the interfaces of specified listings, sleep, wake-up, and reset operations to store the permanent change of the ACPI tables. The ACPI register is to store and transmit the event information between the hardware, the firmware and the ACPI driving program. The ACPI driving program is an OS-level software program to coordinate the transaction between the working state and the sleeping state. 
     The ACPI specification defines a global working state G 0 , in which the host CPU can execute the BIOS command. Under such state, the peripheral apparatus can dynamically change the power state thereof The ACPI specification farther defines a global sleeping state G 1 . Under the state G 1 , the CPU does not execute any user mode thread. The G 1  state comprises sleeping five states S 1  to S 5  for the computer system. In the S 3  sleeping state (which is the called the STR state for the legacy AMP OS, and AMP is a short form of suspend to RAM), it defines that the power other than the one to reserve system memory is not existent. Before the system enters the sleeping state, the BIOS stores all the system hardware (including CPU, cache memory and chipset) configuration information and contexts into the system management RAM (SMRAM) of the system memory. Only the low voltage power (of about 5V) supplied to the system memory and the south bridge chipset is reserved. When a wake-up event is detected, the BIOS resumes all the hardware configuration and enables the hardware operation according to the information stored in the system management RAM. 
     However, while performing power management process, should inconsistency between the operation frequencies of the CPU and the system RAM occur, operations of the system RAM and the CPU cannot be synchronous. More seriously, the computer system may crash while performing power management process. 
     SUMMARY OF THE INVENTION 
     According to the power management process provided by the invention, a system RAM frequency modulation program is stored in a predetermined memory address of the BIOS ROM for the purpose of synchronizing the operation frequencies of the CPU and the system RAM in the power management process. When a power management event occurs, a system interrupt is generated to activate the BIOS program. The CPU is driven to enter the system management mode for operation. When the CPU enters the system management mode to operate, one of the memory address segments of the system RAM is provided as a SMRAM, of which the execution in the SMRAM is irrelevant to the interrupt service routine configured in the system RAM. The shadow RAM control register is programmed by the BIOS program, so that the BIOS ROM is enabled, and the program execution distantly jumps to the predetermined memory address storing the system RAM modulation program of the BIOS ROM. The system RAM modulation program is initiated. 
     When a wake-up event occurs, the BIOS starts executing power-on self test (POST) from the reset vector of the CPU. The hardware including CPU and chipset are thus set up, initiated and enabled. A system interrupt is then requested again to drive the CPU to enter the system management mode operation. In the system management mode, the BIOS drives the CPU to execute other required resume programs. After completing all the resume programs, the program execution jumps to the waking vector of the operating system, so as to return control to the operating system. 
     Both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention, as claimed. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows a block diagram of a computer system; 
         FIG. 2  shows a system address map of a computer system; 
       FIG.  3  and  FIG. 4  show a power suspend process and a power resume process for the ACPI operating system, respectively; and 
       FIG.  5  and  FIG. 6  show a power suspend process and a power resume process for the legacy ACPI operating system, respectively. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to  FIG. 1 , a block diagram of an ACPI computer system  1  is illustrated. The ACPI computer system  1  comprises at least a CPU  101 , for example, an Intel Pentium processor or an AND Athlon processor, a system RAM  102 , a chipset  105 , a host controller  109  and a BIOS ROM  107 . The ACPI computer system  1  has a bus system to provide a mutual connection and communication between various peripherals. The bus system of the computer system  1  includes a first system bus  103 , preferably a peripheral component interconnect (PCI) bus and a second system bus  104 , preferably an industrial standard architecture (ISA) or a low pin count (LPC). An I/O control circuit  106  able to provide an interface to communicate with a keyboard, a parallel port, a serial port, a mouse, a floppy drive and the system bus is further included. The ACPI computer system  1  further provides a plurality of system bus slots  108  into which the system bus peripheral such as a SCS 1  control card is plugged. The host controller  109  is used to coordinate the data transmission between the CPU  101 , the system RAM  102  and the first system bus  103 . The BIOS ROM  107  stores the program command to initiate the computer and to activate and load the operating system. The chipset  105  has a bridge circuit (not shown) to couple the second system bus  104  to the first system bus  103 . The chipset  105  further includes a chip enable circuit (not shown) controlled by the CPU  101  and able to output a ROM chip select signal ROMCS# to selectively enable and disable operation of the BIOS ROM  107 . The BIOS ROM  107  includes a chip enable input pin (not shown in the related figures for the convenience of illustration) to receive the ROM chip enable signal to enable operation of the BIOS ROM  107 , so as to enable the CPU  101  to read the information of the BIOS ROM  107 . 
     Referring to  FIG. 2 , a system address map of a computer system is illustrated. Conventionally, the memory address segments 0 to 9FFFF indicate the conventional memory used for the DOS operating system. The 128K of memory address segments from A0000H to BFFFFH called as the A/B segment are used for video RAM. When the CPU enters the system management mode operation, this memory address segment can be used as a system management random access memory (SMRAM). The memory address segment of 64K from F0000H to FFFFFH is called the F segment and is used to provide the system BIOS to read. The memory space over 1M is called the extended memory area. 
     In the following paragraphs, the terms and related technicalities are defined and explained for people of ordinary skill in the art to fully understand the invention. 
     1. BIOS shadowing: In a general configuration process of the BIOS, a set of command to drive the processor to perform “power-on self test (POST)” is executed. The POST process comprises programs for inspecting the system RAM and the peripherals. In a part of POST process, the data in the BIOS ROM is completely copied to the system RAM. Such process is called the “BIOS shadowing”. The advantage of using BIOS shadowing includes a data access time shorter than that of the BIOS ROM for the system RAM. Thus, the CPU can perform the BIOS program command quickly. Another advantage is that the data stored in the BIOS RAM is possibly in a compressed form. Therefore, the CPU can process the data after copying the data to the system RAM for decompression. In the system RAM, a part of the memory space overlapping the memory space of the BIOS ROM is used as a shadow RAM. The data of the BIOS ROM copied or shadowed to the system RAM will be decompressed (if necessary) and copied to the shadow RAM. Meanwhile, the CPU starts to execute command from the system RAM corresponding to the BIOS ROM address. It is to be noted that after the data of the BIOS memory is copied or shadowed to the system RAM, the chip enable circuit of the chipset disables the BIOS ROM. Generally speaking, the shadow RAM of the BIOS program resides in the F segment (the memory space from F0000H to FFFFFH) of the system RAM. However, when the system management interrupt event occurs, the chipset outputs a control signal SMI# to the CPU, which is then driven to enter the system management mode. When the CPU enters the system management mode operation, the SMRAM used to store the SMI handler routine indicates the A/B segment (the memory space from A0000H-BFFFFH of the system RAM). The BIOS shadow RAM and the SMRAM are the memory space decoded by using the shadow RAM control register of the chipset to control the decoder (not shown) in the chipset. 
     2. The BIOS I/O trap: When the power management event occurs, the OSPM does not configure the power management control command direct into the I/O address where the power management control register is. Instead, the power management control command is set in an unused specific I/O address, and an I/O trap mechanism is used to generate the I/O trap. Generally speaking, the OSPM uses the I/O address of the power management control command to be configured to set up the I/O trap address via a programmable chip select register (generally comprising two registers: programmable chip select (PCS 0 ) and programmable chip select  1  (PCS 1 )). The power management control command is stored in the configured I/O address. When the OSPM configures the configuration value of the power management control commands such as the sleep type (SLP_TYP) and sleep enable (SLP_EN) in the unused I/O address, a SMI control signal is output from the chipset to the CPU, so that the CPU enters the system SMM operation. When the BIOS uses the I/O command to access the I/O addresses, the power management control command is executed to enter a specific sleep state. 
     The power management routine of the invention is explained with the reference of  FIGS. 3  to  6 , accompanied with the system address map as shown in FIG.  2 .  FIG. 3  shows the power suspend routine in the ACPI process system in the invention.  FIG. 4  illustrates the power resume routine in the ACPI process system in the invention. The power suspend routine of the ACPI processing system starts with step  300 . In step  301 , the ACPI processing system continuously detects whether any power management event occurs. In step  302 , the OSPM configures the related power management control command into the unused I/O address required to be configured when one power management event occurs. In step  303 , the OSPM uses the programmable chip select register (PCS 0  and PCS 1 ) to configure the I/O trap address. The BIOS can then access the I/O address with I/O mechanism, so that the power management control command can be executed to enter a specific sleep state. After configuring the I/O trap, in step  304 , a SCI outputs a control signal SCI# from the chipset to the CPU, so as to drive the CPU to enter the system management mode for operation. Generally speaking, when a power management event occurs, it indicates that a hardware interrupt is initiated. The ACPI operating system uses the SCI interrupt handler to respond such event, while the legacy OS system uses SMI interrupt handler to respond such event. The ACPI operating system informs the BIOS of the occurrence of such power management interrupt event (system control interrupt event) via the system control interrupt and returns the control to the BIOS. The BIOS is then responsible for the operation of the power management process. In addition, after generating the system control interrupt, the current storage value of the data structures of the state register SR and the program counter PC are pushed to stack and save. 
     After the CPU outputs a confirm signal to respond the control signal SCI#, the CPU accesses the data in the SMRAM. The CPU jumps to an address of the SMRAM to execute the SCI handler routine. Further, the system control interrupt handler routine activates the SCI service routine according to the occurrence factor of the SCI. The chipset of the ACPI computer system according to the invention further comprises a decoder (not shown) and a shadow RAM control register. Normally, the BIOS will program the shadow RAM control register to decode the F segment of the system RAM as a normal BIOS program for application. The A/B segment of the system RAM is used as the SMRAM to provided to execution of the SCI service routine. 
     In step  305 , the service routine irrelevant to the system RAM is executed at the A/B segment of the system RAM first. In step  306 , the BIOS will program the shadow RAM control register of the chipset. The BIOS shadow memory of the system memory is turned off, and a ROM chip select signal ROMCS# is output to let the BIOS ROM to access data. THE BIOS will program the shadow RAM control register to enable the BIOS ROM, so as to access data from the F segment (memory space from F0000H to FFFFH) of the BIOS ROM. In step  307 , a sequence of BIOS program code is used to change the frequency of the system RAM. When the shadow RAM control register enables the BIOS ROM, the interrupt service routine will distantly jump to the initial address F0000H of the F segment BIOS ROM to start executing the frequency modulation program of the system RAM. The operation frequencies of the system RAM and the CPU are thus synchronized. 
     After the execution of frequency modulation program of the system RAM, the BIOS access the I/O trap address previously configured in step  308 . The power management control command is activated. Thus, the ACPI computer system enters the corresponding sleeping state such as the S 3  sleeping state. The power suspend routine of the ACPI computer system stops at step  309 . 
     The power resume routine of the ACPI operating system of the invention is described as follows with the illustration of FIG.  4 . The power resume routine starts at step  400 . In step  401 , the BIOS starts executing the POST process according to the CPU&#39;s reset vector09e0n the POST process, the BIOS programs processes of the initial power on configuration, initial cache controller and memory controller, the arrangement of cache memory, the enable cache memory and memory controller, the initial chipset of the CPU. In step  403 , the BIOS resumes the operation of the chipset and the system RAM via the hardware state information stored in the SMRAM. In step  404 , the wake-up event drives the chipset to generate a SCI# control signal to the CPU. The CPU outputs a confirm signal to respond the control signal SCI#, and the CPU enters the SMM for operation. In step  405 , all the state information of the hardware is resumed to the initial power on state in the stage of executing the system control interrupt service routine. In step  406 , when the BIOS has arranged and initialize all the hardware structures, the routine returns to the BIOS program from the system control interrupt. In step  407 , the BIOS program distantly jumps to the OSPM waking vector to return the control to the ACPI operating system. The power resume routine of the ACPI operating system ends at step  408 . 
     The power suspend routine and the power resume routine of the legacy APM operating system can be realized from  FIGS. 5 and 6 . In  FIG. 5 , the power suspend routine of the legacy APM operating system is shown. In step  501 , a power management event is detected. In step  502 , the APM operating system may generate a SMI via the software interrupt interface INT  15   h  provided by the BIOS or the power management event (system management interrupt event). Steps  503  to  507  are similar to steps  305  to  309  in FIG.  3 . Further description is not introduced here.  FIG. 6  shows the power resume routine in the legacy APM operating system. The flowchart in  FIG. 6  is similar to the flowchart illustrated in  FIG. 4 , and the introduction is not repeated. 
     The power management process of the invention is characterized by the service routine that synchronizes the operation frequencies of the CPU and the system RAM at a predetermined memory address segment of the BIOS ROM. Using the service routine to synchronize the operation frequencies of the CPU and the system RAM at the BIOS ROM instead of system RAM can ensure the uniqueness of the operation frequency between the system RAM and the CPU during power management process. The reliability of the BIOS under the power management process is improved to reduce the possibility of computer system down. 
     Other embodiments of the invention will appear to those skilled in the art from consideration of the specification and practice of the invention disclosed herein. It is intended that the specification and examples be considered as exemplary only, with a true scope and spirit of the invention being indicated by the following claims.