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Engineer To Engineer Note
EE-202
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Technical Notes on using Analog Devices' DSP components and development tools
Contact our technical support by phone: (800) ANALOG-D or e-mail: dsp.support@analog.com Or visit our on-line resources http://www.analog.com/dsp and http://www.analog.com/dsp/EZAnswers
Using the Expert Linker for Multiprocessor LDFs
Contributed by Maikel Kokaly-Bannourah July 17, 2003
Introduction
This EE-Note explains the use of the Expert Linker (EL) for creating Linker Description Files (LDFs) for Multiprocessor (MP) systems. Although, this concept applies to VisualDSP++ for all SHARC Processor families (ADSP21x6x and ADSP-TSxxx), the examples shown throughout this document are for the ADSPTS101S TigerSHARC Processor. The example code used for this note is based on EE-167 "Introduction to TigerSHARC Multiprocessor Systems Using VisualDSP++" and it was written using VisualDSP++ 3.0 Service Pack 1 for TigerSHARC (please note that "expertlinker_fixes.zip" must be installed prior to going through this note - see README.txt for more details).
refer to the VisualDSP++ 3.0 Linker and Utility Manual for TigerSHARC, EE-69 "Understanding and Using Linker Description Files (LDFs)" (for a general description on the LDF), and EE-167 (for an explanation on the different multiprocessor linker commands).
Expert Linker LDF Wizard
The Expert Linker (EL) wizard is used to generate an LDF for new VisualDSP++ projects. However, the Expert Linker can also be used to view or modify an already existing LDF. Open the project (MP TS101.dpj) attached to this note. The source code comes with no LDF, which will be created, step-by-step, through this note. Please note that an MPTS101_orig_ldf.txt containing an already created LDF file is available as a reference. Let's now get started with the creation of the LDF. First of all, to invoke the Expert Linker wizard choose from the pull-down menu as shown in Figure 1.
Expert Linker Overview
The Expert Linker is a graphical tool that simplifies complex tasks such as memory map manipulation, code and data placement, overlay and shared memory creation, and C stack/heap usage. This tool provides a visualization capability enabling new users to take immediate advantage of the powerful LDF format flexibility in a very user-friendly way. This note assumes a basic understanding of the Linker Description File as well as the way the linker utility (linker.exe) operates. For detailed information on this utility as well as the LDF, please use the VisualDSP++ on-line help. Also,
Figure 1 Invoking the Expert Linker Wizard
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Figure 2 shows the start up window when first invoking the EL wizard.
Figure 3 Project Type Figure 2 Expert Linker Wizard Start-up Window
Click Next.
Selecting an MP LDF
Click Next.
Project type
At this stage, the user needs to specify the project information corresponding to the project type for which the LDF is being generated. As shown in Figure 3, the type can be C, C++, Assembly or VDK. Note that in case a mix of assembly and C files, or any other combination, is used, the most abstract programming language should be selected. For example, for a project with C and assembly files, a C LDF should be selected. Similarly, for a C++ and C project the C++ LDF should be selected. In this particular example, the files source code is assembly, and therefore the selected project type is also Assembly. The LDF name is specified here as well, which by default uses the same as the project name. Note that if an LDF file already exists, the user will be prompted whether to replace the existing file.
By default, the LDF is for single processors. Choose the Multiprocessor box for MP support (Figure 4).
Figure 4 Multiprocessor LDF selection
Determining the Number of Processors and MP Memory Offset Values
Right click on the Processor Properties box to add the desired number of processors to be included in the LDF. For this particular example, a dual processor system is selected. Therefore, a
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second processor (P1) needs to be added to the list.
Figure 6 Executables to Link Against
Figure 5 Processors and MMS Offset
As it can be seen in the Processor window (Figure 5), the multiprocessor memory space (MMS) offset value is automatically added in by the EL. This helps the user to avoid having to worry about specific MP addresses and memory offsets, making the use of MP commands much easier. This is an automatic replacement for the linker command MPMEMORY used in the LDF source file.
Linking Processors Executables
As it would be done in the LDF source file with the LINK_AGAINST command, the EL allows the user to resolve symbols declared within MP space. This is done by simply specifying for each processor to which DSP to link against. In this particular example, symbols referenced in P0 but declared in P1 can be resolved by the linker by adding P1.dxe to the Executable to Link Against box (Figure 6) for P0. Similarly, P0.dxe is added in for P1. In cases where more than one .dxe is added to this box, commas or spaces can be used as separators. Now that an MP LDF has been selected, the processors have been added to the list, and the relevant linker commands have been specified, the LDF is ready for completion. Click Next. Note that in the case where shared external memory is used (shared.sm), this would also need to be added to the link against command box. This is automatically handled by the EL and will be explained later on.
In the Output File box, the user can specify the name of the executable file for each processor in the system. By default, the EL selects the same name for the .dxe file as for the processor name. In this case, P0.dxe and P1.dxe are selected as the names for the DSP executable files and are placed in the Debug folder within the project folder.
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MP LDF Wizard Completion
and Memory Map (tree or representation of each memory map).
graphical
For more details on the Expert Linker window and display options, please use the on-line help in VisualDSP++.
Adding Shared Memory Segments
In many DSP applications where large amounts of memory for multiprocessing tasks and sharing of data are required, an external resource in the form of shared memory may be desired. To add a shared memory section to the LDF using the EL, the following steps should be followed: 1. Right click on the Memory Map pane 2. Select New/Shared Memory 3. Specify a name for the shared memory segment (.SM) 4. Select the DSPs that have access to this shared memory segment. Click OK. As shown in Figure 9, a new shared memory segment, visible to Processors P0 and P1, has been successfully added to the system. Note that variables declared in the shared memory segment will be accessed by both processors in the system. In order for the linker to be able to correctly resolve these variables, the link against command should be used once again (see Linking Processors Executables).
Figure 8 Expert Linker Window
Figure 7 Expert Linker Wizard Completion
Click Finish.
Expert Linker Window
After completion of the Expert Linker wizard, the LDF graphical interface will open up (Figure 8).
The EL window has two panes: Input sections (displays a tree of all the projects input sections)
The EL automatically does this, and therefore the user does not need to perform any additional modifications to the LDF.
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Figure 9 Shared Memory Segment
The user can confirm that the EL has correctly added the .sm file to the link against command line by simply viewing the Memory Map pane properties: 1. Right click on the Memory Map pane 2. Select View Global Properties 3. Click on the Processor tab Shared.sm should now be contained in the Executables to Link Against box for each processor as illustrated in Figure 10.
Figure 10 Adding "shared.sm" to the "Executables to link against" box.
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Detection sections of Non-Linked input
By default, the LDF contains data1, data2 and program input sections for each processor as well as for the shared memory segment. In the scenario where the user declares in his code an input section different to any of the three mentioned above, the EL will detect it and it will mark it with a red cross as a "non-linked" input section (Figure 11).
Figure 11 Detection of non-linked input sections
An example of "non-linked" section is provided in the source code (ext_data). Press the Rebuild All button and update the contents of the EL window (double click on the LDF file in the project window). Figure 11 shows how the linker has detected this "non-linked" input section. In this case, it corresponds to a variable declared in external SDRAM memory, which belongs to the shared memory segment. Note that at this stage, the linker will generate some errors when building the project. This is
due to the fact that the output sections have not been properly configured (object files not linked yet).
Linking Object Files
Now that both processors and the shared memory segments have been properly configured, and the EL has detected all input sections, the next step is to link the object files from these different input sections to their corresponding memory sections.
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First of all, sort the left pane of the Expert Linker window by LDF Macros instead of Input Sections (default setting). This can be done by right clicking on the left pane and selecting Sort by/LDF Macros. Then, right click on the LDF Macro window and add a new macro for P0 (Add/LDF Macro). For example, $OBJECTS_P0. Repeat the same step for P1 and shared.sm (Figure 12). .doj file per processor or shared memory segment, in which case the same step previously explained should be followed for each .doj file. As shown in Figure 14, the LDF macro $COMMAND_LINE_OBJECTS must be deleted from the $OBJECTS macro to avoid duplicate of object files during the linking process. The $COMMAND_LINE_OBJECTS macro contains the .doj files that correspond to every source file used in the project (in this case ID0.doj, ID1.doj and data.doj). If this macro is left in, the linker will automatically map the .doj files for both processors into each processor's memory map, i.e. M0Code/code will contain ID0.doj(program) and ID1.doj(program). This is obviously wrong, since there is no need to map any of ID1.doj code into processor P0. Therefore, right click on the $COMMAND_LINE_OBJECTS macro and select Remove.
Figure 12 Creating LDF Macros
The next step is to add the object files (.doj) that correspond to each processor as well as to the shared memory segment. This is done by right clicking on each recently created LDF Macro and then selecting Add/Object/Library File. Figure 13 shows the objects files added to each LDF Macro.
Figure 14 Deleting the $COMMAND_LINE_OBJECTS LDF Macro
The next step is to map the new macros into memory. This is done by placing each macro into its corresponding memory section.
Figure 13 Adding Object Files
The use of LDF macros becomes extremely useful in systems where there is more than one
Using the Expert Linker for Multiprocessor LDFs (EE-202)
Before this can be done, the left pane needs to be sorted by Input Sections instead of LDF macros.
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Thus, right click on the left pane and select Sort by/Input Sections. Additionally, change in the right pane the Memory Map View Mode from Graphical to Tree mode. Right click on the Memory Map window, select View Mode and then Memory Map Tree. Now select one of the processors by clicking on the processor's name tab. In this case P0 is selected first. Then, place (drag and drop) the recently created LDF macro, $OBJECTS_P0, in its corresponding memory segment. These steps are shown in Figure 15.
Figure 15 Linking Object Files Using LDF Macros
Repeat the same steps for processor P1 ($OBJECTS_P1) and for the shared memory segment, shared.sm (place $OBJECTS_SM in the SDRAM section). Press Rebuild All.
As it can be seen in Figure 16, the red crosses denoting the "non-linked" sections have disappeared, indicating that the input sections have been properly mapped into memory.
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Figure 16 Expert Linker Multiprocessor LDF
Also, note that the LDF macros that were moved from the Input Sections window (left pane) to their corresponding sections in the Memory Map window (right pane) have been automatically replaced during linking process with the actual object files (.doj) used by the linker.
and LINK AGAINST, as well as the corresponding LDF Macros, have been successfully generated by the Expert Linker in a way absolutely transparent to the user. The complete project is now ready to be built. Once again, perform a Rebuild All and safely start debugging with the application code.
Expert Linker Multiprocessor LDF Source Code
The LDF is now complete! Figure 17 illustrates the generated LDF in the Source Code View mode. As shown in Figure 17, the multiprocessor linker commands, MPMEMORY, SHARED MEMORY
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Figure 17 Expert Linker Multiprocessor LDF Source code
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References
[1] ADSP-TS101 TigerSHARC Processor Hardware Reference. First Edition, March 2003. Analog Devices, Inc. [2] VisualDSP++ 3.0 Linker and Utility Manual for TigerSHARC. Rev. 1.0, October 2002. Analog Devices, Inc. [3] Understanding and Using Linker Description Files (LDFs) (EE-69). August 1999. Analog Devices, Inc. [4] Introduction to TigerSHARC Multiprocessor Systems Using VisualDSP++ (EE-167). April 2003. Analog Devices, Inc.
Document History
Version July 17th, 2003 by Maikel Kokaly-Bannourah Description Initial Release
Using the Expert Linker for Multiprocessor LDFs (EE-202)
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