Abstract:
When a peripheral LSI has a memory space which is other than the memory space of a CPU, access is made without one of the memory spaces being aware of the other memory spaces. A flexible bus controller BSC makes address translation according to information on the relation between addresses of both memory spaces. The invention assures wider latitude in CPU type selection and makes it easy to reuse an existing program or develop a new program.

Description:
CROSS-REFERENCE TO RELATED APPLICATION  
       [0001]    This application is related to U.S. application Ser. No. 10/173661 filed on Jun. 19, 2002, the disclosure of which is hereby incorporated by reference. 
     
    
     
       BACKGROUND OF THE INVENTION  
         [0002]    1. Field of the Invention  
           [0003]    The present invention relates to a peripheral LSI in an embedded system of a cellular phone, digital still camera or the like. Here, a peripheral LSI refers to a semiconductor integrated circuit which helps processing by a CPU core.  
           [0004]    2. Description of Related Art  
           [0005]    In recent years, a semiconductor device called a multi-chip module or system-in-package which combines a CPU core chip and a peripheral LSI chip has been increasingly used. Usually a peripheral LSI in this type of semiconductor device starts operation according to a start instruction which it receives from the CPU core.  
           [0006]    The peripheral LSI should transfer data between the CPU core and a peripheral device. As stated on pp.580-609 of “LOGIC AND COMPUTER DESIGN FUNDAMENTALS,” M. MORRIS MANO, 2000, PRENTICE HALL, there are three data transfer methods which are used in such circumstances.  
           [0007]    The first data transfer method is used in a situation which involves processing of large volumes of data as in video encoding. In this method, the peripheral LSI serves as a bus master for data transfer. The second data transfer method uses the CPU core as a bus master. In the third method, a DMAC (direct memory access controller) connected with the CPU bus serves as a bus master for data transfer. In all these three methods, the whole semiconductor device including the peripheral LSI makes up one CPU core memory space.  
         SUMMARY OF THE INVENTION  
         [0008]    With the recent trend of growing demand for higher functionality in semiconductor devices, the peripheral LSI must handle more and more processing tasks. Therefore, it will be convenient if it is possible to replace only the peripheral LSI in the semiconductor device to change the available functions in the semiconductor device. For the whole semiconductor device to make up one CPU core memory space, the CPU core and peripheral LSI must be combined. However, if the memory space of the CPU core is independent from that of the peripheral LSI, it is also possible to freely combine the independent CPU core and the independent peripheral LSI to make up a semiconductor device.  
           [0009]    For this purpose, the memory space of the CPU core and that of the peripheral LSI must be transparent to each other.  
           [0010]    Therefore, according to the present invention, areas in the two memory spaces (CPU memory space and peripheral LSI memory space) which should be transparent to each other are predetermined and address information for these areas is previously stored. Preferably, that address information should be stored in a nonvolatile memory of the semiconductor integrated circuits. If a request for access involving both memory spaces arises, addresses in both memory spaces are translated using the address information.  
           [0011]    Thus, according to the present invention, it is possible to use a versatile peripheral LSI with various functional modules which is suitable for each system, without any increase in design complexity. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]    The invention will be more particularly described with reference to the accompanying drawings, in which:  
         [0013]    [0013]FIG. 1 shows the configuration of a peripheral LSI  33 ;  
         [0014]    [0014]FIG. 2 shows the configuration of a cellular phone (system) which has a semiconductor device including a peripheral LSI according to the present invention;  
         [0015]    [0015]FIG. 3 shows the configuration of a flexible BSC  22 ;  
         [0016]    [0016]FIG. 4 shows the relationship between a peripheral LSI memory space MAP and a CPU memory space MAC;  
         [0017]    [0017]FIG. 5 shows the configuration of an address translation circuit ACON; and  
         [0018]    [0018]FIG. 6 shows the configuration of a bus and power switching circuit BPSW. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0019]    Next, a preferred embodiment of the present invention will be described referring to the accompanying drawings.  
         [0020]    [0020]FIG. 2 schematically shows a semiconductor device SC in a cellular phone as an example. A transmitting/receiving part  47  has a CPU  27 . The main purpose of the CPU  27  is to modulate and demodulate data which is received or sent. The CPU  27  is connected with a memory (MEM 1 ), a flash memory (FLS 2 ), and a peripheral LSI (PLSI)  33 . The peripheral LSI  33  is connected with an I/O bus  1 , and a flash memory (FLS 1 ) the I/O bus is connected with a memory (MEM 2 ), an LCD. controller (LCDC) and a camera (CAM). Thus, a display (LCD) and the camera (CAM) are not directly connected to the CPU bus  21  (system bus) but connected through the peripheral LSI  33 . This prevents large volumes of video data before encoding from occupying the CPU bus  21 .  
         [0021]    The peripheral LSI  33  also uses its internal interface circuit to communicate with an external peripheral device (EDEV)  
         [0022]    Given below are five types of data transfer which may occur in the system shown in FIG. 2.  
         [0023]    Type  1  data transfer concerns data transfer between the flash memory FLS 1  and the peripheral device EDEV. Here, it is the peripheral LSI  33  that serves as a controller LSI which controls this type of data transfer. This is because the flash memory FLS 1  and the peripheral device EDEV are connected through the internal interface circuit (functional module) of the peripheral LSI  33 . Type  1  data transfer involves the memory space of the peripheral LSI  33 .  
         [0024]    Type  2  data transfer concerns data transfer between the flash memory FLS 2  and the peripheral device EDEV. Here, it is the peripheral LSI  33  that serves as a controller LSI which controls this type of data transfer. This is because the flash memory FLS 2  is connected to the CPU bus  21 , the interface circuit for the peripheral device EDEV is built in the peripheral LSI  33  and thus both (FLS 2  and EDEV) are visible to the peripheral LSI  33 . Type  2  data transfer involves both the memory space of the CPU  27  and that of the peripheral LSI  33 . If a program for control of the peripheral device EDEV is stored in the program area of the flash memory FLS 2 , the system sends this program to the peripheral device EDEV to control it.  
         [0025]    Type  3  data transfer involves neither data processing as stated later nor the abovementioned data transfer with the peripheral device EDEV. This type of data transfer relates to, for example, a case that the data stored in the memory MEM 1  is shown on the LCD. Type  3  data transfer also involves both the memory space of the CPU  27  and that of the peripheral LSI  33 . However, unlike Type  2  data transfer, the controller LSI for this type of data transfer is a DMA controller (not shown) connected to the CPU  27  or CPU bus  21 . In Type  3  data transfer, the peripheral LSI  33  is only responsible for bus control. Data from the memory MEM 1  is sent to the CPU bus  21  and the peripheral LSI  33  sends the data from the CPU bus  21  through the I/O bus  1  to the LCD. For example, Type  3  data transfer is done in order to show a message to notify arrival of an e-mail in the standby mode of a cellular phone.  
         [0026]    Data transfer Type  4  and Type  5  relate to system level operation which uses an IP (functional module) for data processing, built in the peripheral LSI  33 . The peripheral LSI  33  serves as the controller LSI for both Type  4  and Type  5  of data transfer. Type  4  data transfer and Type  5  data transfer also involve both the memory space of the CPU  27  and that of the peripheral LSI  33 .  
         [0027]    An example of operation for Type  4  data transfer is a sequence in which received data is processed and the processed data is displayed. After the CPU  27  stores the received data in the memory MEM 1 , the peripheral LSI  33  sends the data from the memory MEM 1  through the CPU bus  21  to the peripheral LSI  33 , which then processes the data and sends the processed data through the IO bus  1  to the LCD. One concrete example is video messaging (receiving) where encoded video data is received and decoded by the peripheral LSI  33  for showing on the LCD.  
         [0028]    An example of operation for Type  5  data transfer is a sequence in which data entered via a data input device is processed and sent. Video data from the camera (CAM) is loaded via a special purpose data line  48  into the peripheral LSI  33  and processed and sent through the CPU bus  21  to the CPU  27 . One concrete example is video messaging (sending) where moving images captured by the camera is encoded by the peripheral LSI  33  and the encoded data is sent.  
         [0029]    Next, an explanation will be given of the configuration of the peripheral LSI and its operational sequences for the implementation of the abovementioned data transfers.  
         [0030]    (1) Configuration of the Peripheral LSI  
         [0031]    [0031]FIG. 1 outlines the configuration of the peripheral LSI. The peripheral LSI  33  incorporates a plurality of functional modules. These modules are: CODEC circuits for image encoding and decoding, GRP; a video input/output circuit for large volumes of data communications with a camera or the like, VIO; a two-way serial bus IIC; and an interface circuit group  5  for serial data communications with the peripheral device EDEV. This interface circuit group  5  includes a USB interface circuit  5 - 1 , a Bluetooth interface circuit  5 - 2  and a serial input/output interface circuit  5 - 3 . The CODEC circuits GRP are application-specific circuits which comply with, for example, MPEG4 protocol. Since the CODEC circuits GRP, video input/output circuit VIO and two-way serial bus IIC have high data transfer rates, they are connected to an internal bus  3  with a high transfer rate, while the interface circuit group  5  is connected to a peripheral bus  4  with a low transfer rate. As will be explained later, the peripheral LSI according to the present invention can select whether or not to use an internal functional module depending on the functionality of a semiconductor device in use. A bus and power switching circuit BPSW is provided for this purpose. It stops power supply to a functional module which is not to be used, and disconnects the bus connection with the module. If no such selection function is provided, the bus and functional modules may be connected directly, or without intermediation of the switching circuit BPSW.  
         [0032]    A flexible bus controller FBSC  22  controls data transfer by the peripheral LSI  33 . For data transfer which involves both the memory space of the CPU  27  and that of the peripheral LSI  33 , the flexible BSC  22  uses address translation information for mapping between the memory space of the CPU  27  and that of the peripheral LSI  33 . This address translation information is stored in an on-chip flash memory IFLS through an external pin  69 . Memory read circuits IFLSR read the address translation information stored in the on-chip flash memory IFLS and send it to the flexible BSC  22 .  
         [0033]    Interrupt control circuits INTC receive various interrupt signals which include bus requests from the functional modules.  
         [0034]    (2) Internal Operational Sequences of the Peripheral LSI  
         [0035]    Internal operational sequences of the peripheral LSI  33  to implement the above five types of data transfer are described below.  
         [0036]    (a) Type  1  Data Transfer  
         [0037]    A flash interface circuit (not shown, hereinafter referred to as “flash IF”) is used as the interface circuit for the flash memory FLS 1 , and the USB interface circuit  5 - 1  and the Bluetooth interface circuit  5 - 2  are used as the interface circuits for the peripheral device EDEV. Since relatively low transfer rates are usable for these interface circuits, not the interface circuits but an on-chip CPU (ICPU)  6  serves as a bus master.  
         [0038]    The sequence of data transfer from the flash memory FLS 1  to the peripheral device EDEV is as follows. First, data is transferred from the flash memory FLS 1  through the flash IF to the peripheral bus  3 . Then the data is sent through the flexible BSC  22  to the register of the on-chip CPU  6  (ICPU). The on-chip CPU  6  transfers the data in the register through the flexible BSC  22  to the peripheral bus  3 . Lastly, the data on the peripheral bus  3  is transferred through the register of the USB or Bluetooth interface circuit to the peripheral device. The sequence of data transfer from the peripheral device EDEV to the flash memory FLS 1  is the reverse of the above.  
         [0039]    (b) Type  2  Data Transfer  
         [0040]    For the same reason as in the case of Type  1  data transfer, the on-chip CPU  6  serves as a bus master. In data transfer from the flash memory FLS 2  to the peripheral device EDEV, data is first sent from the flash memory FLS 2  through the CPU bus  21  to the flexible BSC  22 , from which the data is then sent to the register of the on-chip CPU 6 . The subsequent steps for data transfer are the same as in the case of Type  1  data transfer.  
         [0041]    (c) Type  3  Data Transfer  
         [0042]    In Type  3  data transfer, the peripheral LSI  33  is only responsible for bus control. Data is transferred from the memory MEM 1  through the CPU bus  21  to the flexible BSC  22 . From the flexible BSC  22 , the data is sent through the IO bus  1  and the memory MEM 2  to a display control circuit LCDC. The display control circuit LCDC displays the data on the LCD.  
         [0043]    (d) Type  4  Data Transfer and Type  5  Data Transfer  
         [0044]    In Type  4  data transfer and Type  5  data transfer, the CPU bus  21 , IO bus  1  and peripheral LSI  33  are all involved, so the peripheral LSI  33  servers as a controller LSI. The bus master here is a functional module like the CODEC circuits GRP which perform data processing. This is because data transfer without intermediation of the on-chip CPU  6  is more advantageous in order to meet the need for high speed data processing.  
         [0045]    The sequence of Type  4  data transfer is explained below, taking an example of video data decoding and display using the CODEC circuits GRP. First, data is transferred from the memory MEM 1  through the CPU bus  21  to the flexible BSC  22 , from which the data is transferred through the internal bus  4  to the CODEC circuits GRP. Then, the CODEC circuits GRP decode the video data and send the decoded data through the internal bus  4  to the flexible BSC  22 . From the flexible BSC  22 , the data is sent through the IO bus  1  to the memory MEM 2 . The subsequent steps are the same as in the case of Type  3  data transfer.  
         [0046]    The sequence of Type  5  data transfer is similar to that of Type  4  data transfer. As shown in FIG. 2, either the IO bus  1  or the special purpose data lines  48  may be used for the route of data loading.  
         [0047]    (3) Functions of the Flexible BSC  22   
         [0048]    The main functions of a bus controller are bus state control and decoding/generation of a bus protocol. Bus state control refers to a process of judging the bus state according to a read/write request from a CPU or other device and decoding or generating a bus protocol. Like a known bus controller, the flexible BSC  22  also has these functions.  
         [0049]    The bus controller also generates a protocol to send data to a bus and decodes it to receive data from a bus. When there are a plurality of buses as in the present invention, protocol generation and decoding are done for a bus for sending data and a bus for receiving data, respectively. Particularly in data transfer Types  2  to  5 , more than one memory space are involved. Therefore, mapping between memory spaces is made for decoding or generation of a protocol in the flexible BSC and translation of addresses to be mapped must be made. This function enables access to another memory space without a complicated process such as a program modification, thereby reducing the system development cost.  
         [0050]    (4) Configuration of the Flexible BSC and its Operation  
         [0051]    [0051]FIG. 3 shows the configuration of the flexible BSC  22 . The flexible BSC  22  has a bus state controller BSTC and protocol decode and generation circuits PAG. The bus state controller BSTC accepts bus requests from a circuit which can be a bus master (for example, the on-chip CPU  6 , a functional module such as the CODEC circuits GRP, or the CPU  27 ) and buses for data transfer and releases the requested bus right in the order of priority. At this time, it changes the bus state and sends information on buses for data transfer to the bus protocol decode and generation circuits PAG. These buses are all buses associated with the flexible BSC  22 , namely the CPU bus  21 , IO bus  1 , internal bus  4  and peripheral bus  3 .  
         [0052]    As the bus protocol decode and generation circuits PAG receive bus information from the bus state controller BSTC, the circuits decode or generate a protocol and perform address translation of necessary memory spaces.  
         [0053]    The bus information which is sent from the bus state controller BSTC to the bus protocol decode and generation circuits PAG includes the following three types of signals: a first bus signal  28  which indicates whether or not it is buss access to the peripheral LSI  33 ; a second bus signal  39  which indicates whether or not two memory spaces are involved for the bus access; and a third bus signal  29  which indicates whether or not it is CPU bus access. These three types of bus signals are respectively used to control a peripheral LSI protocol decode and generation circuit PPAG, an address translation circuit ACON, and a CPU protocol decode and generation circuit CPAG. The first bus signal  28  becomes active when there occurs access to a bus related to the memory space of the peripheral LSI (IO bus  1 , internal bus  4  or peripheral bus  3 ). The second bus signal  39  becomes active when there occurs access involving both memory spaces. The third bus signal  29  becomes active when there occurs access to a bus unrelated to the memory space of the peripheral LSI (CPU bus  21 ).  
         [0054]    Type  1  data transfer is data transfer which is processed within the memory space of the peripheral LSI. In this case, the first bus signal  28  is active while the second bus signal  39  and the third bus signal  29  are inactive. Data transfer is processed only within one memory space in this way.  
         [0055]    In Type  2  data transfer, first, the on-chip CPU  6  issues a bus master request for the CPU bus  21  to the bus state controller BSTC through a control line  26 . The bus state controller BSTC issues a bus request Req to the CPU  27  through a control line  18  and receives an acknowledgement Ack. This gives permission for data transfer from the IO bus  1 . (or internal bus  4  or peripheral bus  3 ) to the CPU bus  21 . The bus state controller BSTC activates the first bus signal  28  in order to enable the peripheral LSI protocol decode and generation circuit PPAG to obtain data from the IO bus  1 . Also address translation is needed to send the transferred data to the peripheral bus  3 . Thus, the bus state controller BSTC activates the second bus signal  39  as well. The address translation circuit ACON translates the peripheral LSI memory space address obtained from an address bus  50  into an address for the CPU memory space. The CPU protocol decode and generation circuit CPAG sends the CPU memory space address as a result of translation by the address translation circuit ACON to an address bus  51  and the data to the CPU bus  21 .  
         [0056]    In Type  3  data transfer, the CPU  27  issues a bus request Req to the bus state controller BSTC through the control line  18  and receives an acknowledgement Ack. This gives permission for data transfer from the CPU bus  21  to the IO bus  1  (or internal bus  4  or peripheral bus  3 ). The bus state controller BSTC activates the third bus signal  29  in order to enable the CPU protocol decode and generation circuit CPAG to obtain data from the CPU bus  21 . Address translation is needed to send the transferred data to the IO bus  1 . Thus, the bus state controller BSTC activates the second bus signal  39  as well. The address translation circuit ACON translates the CPU memory space address obtained from the address bus  50  into an address for the peripheral LSI memory space. The peripheral LSI protocol decode and generation circuit PPAG sends the peripheral LSI memory space address as a result of translation by the address translation circuit ACON to the address bus  50  and the data to the IO bus  1 .  
         [0057]    (5) Configuration of the Address Translation Circuit and its Operation  
         [0058]    [0058]FIG. 4 shows address translation for mapping between the peripheral LSI  33  memory space MAP and the CPU  27  memory space MAC. There will be the following two cases: case A in which the peripheral LSI  33  serves as a bus master and access is made to the memory space of the CPU  27 ; and case B in which the CPU  27  serves as a bus master and access is made to the memory space of the peripheral LSI  33 .  
         [0059]    In case A, a memory range (second range) in the memory space of the peripheral LSI  33  is allocated to the memory range in the CPU  27  to be accessed (first range). Information necessary for address translation are the start address CA 1  in the first range, the start address PA 1  corresponding to the start address CA 1 , and the address width RG 1  of the first range.  
         [0060]    Case B is opposite to case A. Information necessary for address translation are the start address PA 2  in the memory range in the peripheral LSI  33  to be accessed (third range), the start address CA 2  in the CPU memory range (fourth range) corresponding to the start address PA 2 , and the address width RG 2  of the third range.  
         [0061]    The abovementioned address information is stored in the on-chip flash memory IFLS. As the peripheral LSI  33  is initialized, the information is read from the on-chip flash memory IFLS into the registers of the address translation circuit (see FIG. 5). The start address CA 1 , start address PA 1  and address width RG 1  are stored in registers CA 1 -Reg, PA- 1 -Reg, and RG 1 -Reg, respectively. Likewise, the start address CA 2 , start address PA 2  and address width RG 2  are stored in registers CA 2 -Reg, PA 2 -Reg, and RG 2 -Reg, respectively.  
         [0062]    Although there are two different cases that address translation is needed (from the peripheral LSI memory space to the CPU memory space or vice versa), a similar operational sequence is used in both the cases. Therefore, only the case that the peripheral LSI  33  as a bus master accesses the CPU memory space is explained below.  
         [0063]    First, the address to be accessed (address in the peripheral LSI memory space MAP which belongs to the second range shown in FIG. 4; here called the “first address”) from the peripheral LSI protocol decode and generation circuit PPAG is sent to the address translation circuit ACON. The first address is written through a selector W-SEL 1  into a register PA-Reg. In this case, the values of registers CA 1 -Reg, PA 1 -Reg, and RG 1 -Reg are read into an address selection circuit ASEL which decides whether or not the first address written in the register PA-Reg belongs to the second range. If it does not belong to the second range, an error signal  61  is sent to an interrupt circuit INTC. If it belongs to the second range, an address calculation circuit ACAL translates it into an address in the CPU memory space MAC. The new address (here called the “second address”) is calculated from the formula: CA 1  (address on CA 1 -Reg)+(address on PA-Reg)−PA 1  (address on PA 1 -Reg). The second address is written through a selector W-SEL 2  into a register CA-Reg. The second address written in the register CA-Reg is sent to the CPU protocol decode and generation circuit CPAG.  
         [0064]    The same operational sequence as above is used for the case that the CPU  27  serves as a bus master. In this case, however, the new address is calculated from the formula: PA 2  (address on PA 2 -Reg)+(address on CA-Reg)−CA 2  (address on CA 2 -Reg).  
         [0065]    (6) Initialization  
         [0066]    When the peripheral LSI  33  is initialized, the data in the on-chip flash memory IFLS is read into the register groups  60   a  and  60   b  using a read circuit IFLSR. The read circuit IFLSR incorporates a read sequencer SQS and a memory interface circuit MIF.  
         [0067]    The bus state controller BSTC notifies the read circuit IFLSR of a request for initialization according to an input signal such as a power-on reset signal through a data line  17 . According to this notification, the read sequencer SQS sends an instruction to the memory interface circuit MIF and reads the data in a predetermined address order successively. The read data is sent to the address translation circuit ACON where a selector W-SEL 3  determines the registers to store it and the data is stored in the register groups  60   a  and  60   b.    
         [0068]    (7) Bus and Power Switching Circuit  
         [0069]    It is desirable that various functional modules be incorporated in the peripheral LSI  33  to cope with various systems. However, some of the incorporated functional modules may not be used. Therefore, waste of electric power caused by current flows to modules not in use or malfunctioning should be prevented. FIG. 6 shows a switching circuit which disconnects a module not in use from a bus and turns off the power to the module. Although the peripheral bus  3  is connected with the module as the connection bus in the example shown in FIG. 6, operation of the circuit is the same when the internal bus  4  is connected.  
         [0070]    The switching circuit BPSW has switch elements  240  between a power supply line  43  and functional modules, and switch elements  230  between the bus  3  and functional modules. Switch elements  230 - 1  and  240 - 1  for a functional module  5 - 1  are controlled by a first control signal while switch elements  230 - 2  and  240 - 2  for a functional module  5 - 2  are controlled by a second control signal.  
         [0071]    When a control signal activates a switch element, data transfer between a functional module and the peripheral bus becomes possible, the power is supplied and the functional module becomes active. On the other hand, when a control signal inactivates the switch element, data transfer between the functional module and the peripheral bus becomes impossible, there is no power supply and the module becomes inactive. A register Sel-Reg stores such control signals where a control signal for activating a switch element is stored as 1 and a control signal for inactivating it is stored as 0.  
         [0072]    As described above, module activation/inactivation is controlled according to the register Sel-Reg. The activation/inactivation data is stored in the on-chip flash memory IFLS. It is read by the read circuit IFLSR when the peripheral LSI  33  is initialized, and written into the register Sel-Reg. Initialization takes place as mentioned above.  
         [0073]    A preferred embodiment of the present invention has been so far explained but the invention may be embodied in other forms. In the example shown in FIG. 2, the CPU  27  and peripheral LSI  33  are mounted on a board. However, they may be mounted on different boards. For example, it is also possible to mount the CPU  27  on a first board and the peripheral LSI  33  on a second board, connect the first and second boards by a routing layer and seal them as a package.  
         [0074]    Furthermore, a nonvolatile memory or a volatile memory with power backup may be used in place of the on-chip flash memory IFLS. A nonvolatile memory which may be used here is an ultraviolet ray erasable EPROM or fuse. It is also acceptable that such a memory is provided as an external chip instead of being built in the peripheral LSI  33 .  
         [0075]    According to the present invention, control signals (address information for the flexible BSC  22  and functional module selection information for the bus and power supply switching circuit BPSW) are stored in the on-chip flash memory IFLS, which permits the use of the same peripheral LSI  33  in various systems. It is desirable that writing into the on-chip flash memory IFLS be done in the form of a wafer (pre-chip stage) before a probing test. This eliminates the need for connection of a pin in the package to apply a high voltage for writing into the on-chip flash memory IFLS and thus prevents writing after packaging. In testing the peripheral LSI according to the present invention, the functional module selected by the bus and power supply switching circuit BPSW should be tested but testing of other functional modules may be omitted.