backup_sram.cpp

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#include <cstring> //For memcpy
#include "stm32f4xx_pwr.h"
#include "stm32f4xx_rcc.h"
#include "backup_sram.h"

void backup_sram_init()
{
  //The checksum function depends on the BackupData struct being a multiple of 32 bits
  //If you change the BackupData struct, and it trips on this static_assert,
  //either make the BackupData struct a multiple of 32 bits, or change the checksum method
  static_assert(sizeof(rosflight_firmware::BackupData)%4==0,"Error with debug_info_t: Size is not multiple of 32 bits");
#pragma GCC diagnostic push //Ignore old style cast from included library
#pragma GCC diagnostic ignored "-Wold-style-cast"
  RCC_APB1PeriphResetCmd(RCC_APB1Periph_PWR, DISABLE);
  RCC_APB1PeriphClockCmd(RCC_APB1Periph_PWR, ENABLE);
  RCC_AHB1PeriphClockCmd(RCC_AHB1Periph_BKPSRAM, ENABLE);
#pragma GCC diagnostic pop
  PWR_BackupRegulatorCmd(ENABLE);
}

void backup_sram_write(const rosflight_firmware::BackupData &data)
{
  PWR_BackupAccessCmd(ENABLE);
#pragma GCC diagnostic push //Ignore old style cast from included library
#pragma GCC diagnostic ignored "-Wold-style-cast"
  std::memcpy(reinterpret_cast<void *>(BKPSRAM_BASE),&data,sizeof(rosflight_firmware::BackupData));
#pragma GCC diagnostic pop
  PWR_BackupAccessCmd(DISABLE);
}

//This method actually reads the backup sram, and then clears it.
//This is used by the backup_sram_read() function, and should not
//be used elsewhere.
rosflight_firmware::BackupData do_first_read()
{
#pragma GCC diagnostic push //Ignore old style cast from included library
#pragma GCC diagnostic ignored "-Wold-style-cast"
  rosflight_firmware::BackupData data = *(reinterpret_cast<rosflight_firmware::BackupData *>(BKPSRAM_BASE));
#pragma GCC diagnostic pop
#pragma GCC diagnostic push //Ignore blank fields in struct
#pragma GCC diagnostic ignored "-Wmissing-field-initializers"
  rosflight_firmware::BackupData blank_data = {0};
#pragma GCC diagnostic pop
  if (!check_backup_checksum(data))
    data=blank_data;
  backup_sram_write(blank_data);
  return data;
}

rosflight_firmware::BackupData backup_sram_read()
{
  static rosflight_firmware::BackupData data = do_first_read();
  return data;
}

bool check_backup_checksum(const rosflight_firmware::BackupData &data)
{
  return (data.checksum==generate_backup_checksum(data));
}

//Generates a checksum by XORing 32 bit chunks of the backup data together,
//excluding the last 32 bits, which stores the checksum itself
uint32_t generate_backup_checksum(const rosflight_firmware::BackupData &data)
{
  const uint32_t *pointer = reinterpret_cast<const uint32_t *>(&data);
  uint32_t checksum = 0;
  for (uint8_t i=0; i<(sizeof(rosflight_firmware::BackupData)/4)-1; i++)
    checksum^=*(pointer+i);
  return checksum;
}