6663b6c9
 adorian
projet complet av...
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#include <ion/usb.h>
#include <string.h>
#include <assert.h>
extern char _stack_end;
extern char _dfu_bootloader_flash_start;
extern char _dfu_bootloader_flash_end;
namespace Ion {
namespace USB {
typedef void (*PollFunctionPointer)(bool exitWithKeyboard);
void DFU() {
/* DFU transfers can serve two purposes:
* - Transfering RAM data between the machine and a host, e.g. Python scripts
* - Upgrading the flash memory to perform a software update
*
* The second case raises a huge issue: code cannot be executed from memory
* that is being modified. We're solving this issue by copying the DFU code in
* RAM.
*
* The new DFU address in RAM needs to be temporarily overwriteable when the
* program is being run. Epsilon has a large stack to allow deeply recursive
* code to run, but when doing DFU transfers it is safe to assume we will need
* very little stack space. We're therefore using the topmost 8K of the stack
* reserved by Epsilon. */
/* 1- The stack being in reverse order, the end of the stack will be the
* beginning of the DFU bootloader copied in RAM. */
size_t dfu_bootloader_size = &_dfu_bootloader_flash_end - &_dfu_bootloader_flash_start;
char * dfu_bootloader_ram_start = reinterpret_cast<char *>(&_stack_end);
assert(&_stack_end == (void *)(0x20000000 + 256*1024 - 32*1024));
/* 2- Verify there is enough free space on the stack to copy the DFU code. */
char foo;
char * stackPointer = &foo;
if (dfu_bootloader_ram_start + dfu_bootloader_size > stackPointer) {
// There is not enough room on the stack to copy the DFU bootloader.
return;
}
/* 3- Copy the DFU bootloader from Flash to RAM. */
memcpy(dfu_bootloader_ram_start, &_dfu_bootloader_flash_start, dfu_bootloader_size);
/* 4- Jump to DFU bootloader code. We made sure in the linker script that the
* first function we want to call is at the beginning of the DFU code. */
PollFunctionPointer dfu_bootloader_entry = reinterpret_cast<PollFunctionPointer>(dfu_bootloader_ram_start);
/* To have the right debug symbols for the reallocated code, break here and:
* - Get the address of the new .text section
* In a terminal: arm-none-eabi-readelf -a ion/src/device/usb/dfu.elf
* - Delete the current symbol table
* symbol-file
* - Add the new symbol table, with the address of the new .text section
* add-symbol-file ion/src/device/usb/dfu.elf 0x20038000
*/
dfu_bootloader_entry(true);
/* 5- That's all. The DFU bootloader on the stack is now dead code that will
* be overwritten when the stack grows. */
}
}
}
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