3 ROM Bootloader

At the beginning, the device boots and, based on the boot mode, decides if it should execute code already programmed into the Flash memory or load in code using one of the ROM loaders. This application report focuses on the boot execution path when the emulator is not connected.

After the boot ROM readies the device for use, it decides where it should start executing. In the case of a standalone boot, it does this by examining the state of two GPIOs (as seen in Table 3-1 , the default choices are GPIO 24 and 32). In some cases, two values programmed into one time programmable (OTP) memory can be examined. In the implementation described in this application report, the SCI loader is used, so at power up GPIO 32 must be forced high and GPIO 24 must be forced low. If this is the case when the device boots, the SCI loader in ROM begins executing and waits to autobaud lock with the host (for a character to be received in order to determine the baud rate at which the communications will occur). At this point, the device is ready to receive code from the host.

The ROM loader requires data to be presented to it in a specific structure. The structure is common to all ROM loaders and is described in detail in the Bootloader Data Stream Structure section of [1] . You can easily generate your application in this format by using the hex2000 utility included with the TI C2000 compiler. This file format can even be generated as part of the Code Composer Studio build process by adding a post-build step with the following options:

"${CG_TOOL_HEX}" "${BuildArtifactFileName}" -boot -sci8 -a -o "${BuildArtifactFileBaseName}.txt"

For the CM core in F2838x, the following command can be used:

"${CG_TOOL_HEX}" "${BuildArtifactFileName}" -boot -gpio8 -a -o "${BuildArtifactFileBaseName}.txt"

Alternatively, you can use the TI hex2000 utility to convert COFF and EABI .out files into the correct boot hex format. To do this, you need to enable the C2000 Hex Utility under Project Properties. The command is below:

hex2000.exe -boot -sci8 -a -o <file.txt> <file.out>

For the CM core in F2838x, the following command can be used:

armhex.exe -boot -gpio8 -a -o <file.txt> <file.out>

As stated before, ROM loaders can only load code into RAM, which is why they are used to load in flash kernels, which will be described in Section 4 and Section 5.