B.1 Scenario 1: Building a Hex Conversion Command File for a Single 8-Bit EPROM

Scenario 1 shows how to build the hex conversion command file for converting an object file for the memory system shown in Figure B-1. In this system, there is one external 128K × 8-bit EPROM interfacing with a TMS470 target processor.

A object file consists of blocks of memory (sections) with assigned memory locations. Typically, all sections are not adjacent: there are holes between sections in the address space for which there is no data. Scenario 1 shows how you can use the hex conversion utility’s image mode to fill any holes before, between, or after sections with a fill value.

For this scenario, the application code resides in the program memory (ROM) on the TMS470 CPU, but the data tables used by this code reside in an off-chip EPROM.

The circuitry of the target board handles the access to the data; the native TMS470 address of 0x1000 accesses location 0x0 on the EPROM.

To satisfy the address requirements for the code, this scenario requires a linker command file that allocates sections and memory as follows:

• The program/application code (represented in this scenario by the secA section shown in Example 1) must be linked so that its address space resides in the program memory (ROM) on the TMS470 CPU.
• To satisfy the condition that the data be loaded on the EPROM at address 0x0 but be referenced by the application code at address 0x1000, secB (the section that contains the data for this application) must be assigned a linker load address of 0x1000 so that all references to data in this section will be resolved with respect to the TMS470 CPU address. In the hex conversion utility command file, the paddr option must be used to burn the section of data at EPROM address 0x0. This value overrides the section load address given by the linker.

Example 1 shows the linker command file that resolves the addresses needed in the stated specifications.