Download and run whole application in RAM (Cortex-M3)

Introduction

You have a need to run a complete application in RAM.

Limitation

This suggestion will only work when downloading with the C-SPY debugger.
If you need to run in RAM stand-alone, then go to Technical Note 11578.

Discussion

Background:

These are the steps needed to get the whole application placed in RAM, and to get it to run as expected in RAM.

• Change so that data (read/write and constant) and code are linked to be placed in RAM.
• Place the Vector Table in RAM (with at least the alignment forced by the Cortex-M design.)
• During C-start-up, set VTOR to the address of the Vector Table.

Suggested solution:

There are different ways to make a solution, so these suggestions are just one possibility.

Place CODE and DATA in RAM.

• Use the "edit"-button (or change directory in your .icf file) at Project > Options > Linker > Config to open the window "Linker configuration file editor"
• Go to the page "memory regions"
  • copy the value in RAM/start and paste that value in ROM/start
  • then copy the value in RAM/end and paste it as ROM/end.

Check that CODE, DATA and Vector table are placed in RAM

Build the project.

• Check (in the .map file) that the Vector Table (symbolic name is __vector_table ) is placed in RAM and at an address that is aligned to 2^7.
• If needed to change go to page Project > Options > Linker > Config > Vector table.
  • There change to an address in RAM that is aligned to 2^7 (a suggestion is to use address 0x20000000)

Set VTOR RAM

Change VTOR ("Vector Table Offset Register") to point to the location in RAM for the Vector Table (symbolic name __vector_table ).

• Take a copy of the file \arm\src\lib\low_level_init.c and add the coppiced file to your project. (You might need to remove write protection from the file.)
• Add an #include statement for the device in use. (That is to get a reference to the header (.h) holding the definition of the register VTOR.)
• Add a declaration for ... extern int __vector_table[]; ...the Vector Table
• In the function __low_level_init set VTOR to the address of __vector_table, which can be done as:

VTOR = (unsigned int) & __vector_table;

Test that VTOR is correctly set.

• Build the modified project.
• Download into the Simulator.
  • Check that VTOR is set to the address of the Vector Table in RAM.
• Change from Simulator to your hardware debugger driver.
• Download to RAM and run the application there.

Example project

On the link below there is an example project for STM32F103ZE.

Example STM32F103ZE.zip

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