borgware-2d/random/persistentCounter.c

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/**
* \file persistentCounter.c
* \author Daniel Otte
* \brief a persistent 24-bit counter in EEPROM for ATmega µC
*
*/
#include <stdint.h>
#include <avr/interrupt.h> /* cli() & sei() */
#include <avr/eeprom.h>
#include "../config.h"
#ifdef ERROR_HANDLING
#include "error-handling.h"
#define PERSISTENT_COUNTER_OVERFLOW (void*)0, 2,4,1
#define PERSISTENT_COUNTER_WRITER_ERROR (void*)0, 2,4,2
#endif
#define RING_SIZE 168
uint8_t ring_idx = 0xff;
uint16_t EEMEM B08_23;
uint8_t EEMEM B0_7[RING_SIZE];
#ifdef INIT_EEPROM
void init_buffer(void){
uint8_t i;
eeprom_busy_wait();
eeprom_write_word(&B08_23, 0x0000);
for(i=0; i<RING_SIZE; ++i){
eeprom_busy_wait();
eeprom_write_byte(&(B0_7[i]), 0x00);
}
}
#endif
void percnt_init(void){
uint8_t i;
uint8_t maxidx=0;
uint8_t t,max=eeprom_read_byte(&(B0_7[0]));
#ifdef INIT_EEPROM
if (eeprom_read_word(&B08_23)==0xFFFF){ /* test if the 2 MSB == 0xFFFF*/
if (eeprom_read_word((uint16_t*)&(B0_7[0]))==0xFFFF) /* test the first to bytes of ringbuffer*/
init_buffer();
}
#endif
for(i=0; i<RING_SIZE; ++i){ /* this might be speed up, but such optimisation could lead to timing attacks */
eeprom_busy_wait();
t=eeprom_read_byte(&(B0_7[i]));
if(t==max+1){
max=t;
maxidx=i;
}
}
ring_idx = (maxidx==RING_SIZE)?0:maxidx;
}
uint32_t percnt_get(void){
uint32_t ret=0;
if(ring_idx==0xff)
percnt_init();
cli();
eeprom_busy_wait();
ret=eeprom_read_word(&B08_23)<<8;
eeprom_busy_wait();
ret |= eeprom_read_byte(&(B0_7[ring_idx]));
sei();
return ret;
}
void percnt_inc(void){
/* we must make this resistant agaist power off while this is running ... */
uint32_t u;
if(ring_idx==0xff)
percnt_init();
u = percnt_get();
cli();
/* it's important to write msb first! */
if((u&0x000000ff) == 0xff){
if((u&0x0000ffff) == 0xffff){
if((u&0x00ffffff) == 0xffffff){
/* we can turn the lights off now. it's time to die */
#ifdef ERROR_HANDLING
error(PERSISTENT_COUNTER_OVERFLOW);
#endif
}
eeprom_busy_wait();
eeprom_write_byte(&(((uint8_t*)&B08_23)[1]),((u+1)>>16)&0xff);
}
eeprom_busy_wait();
eeprom_write_byte(&(((uint8_t*)&B08_23)[0]),((u+1)>>8)&0xff);
}
/* set least significant byte (in ringbuffer) */
ring_idx = (ring_idx+1)%RING_SIZE;
eeprom_busy_wait();
eeprom_write_byte(&(B0_7[ring_idx]),(u+1)&0xff);
eeprom_busy_wait();
if(u+1 != percnt_get()){
#ifdef ERROR_HANDLING
error(PERSISTENT_COUNTER_WRITER_ERROR);
#endif
}
sei();
}