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storage.c
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storage.c
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#include <avr/eeprom.h>
#include "libarduino2.h"
#include "storage.h"
#define EEPROM_BEGIN 0
#define EEPROM_END 1024
#define EEPROM_EOF (EEPROM_END + 1)
#define EEPROM_ERROR (EEPROM_END + 2)
uint16_t storage_sum(table_t const *table) {
uint8_t const *data = (uint8_t const *)(table + 1);
uint16_t sum = 0;
int i;
for (i = 0; i < table->len - sizeof(table_t); ++i) {
sum += data[i];
}
return sum;
}
void storage_clear(void) {
table_t end = { 0 };
eeprom_write_block(&end, (void *)EEPROM_BEGIN, sizeof(table_t));
}
uint16_t storage_find(uint16_t id, table_t *table) {
uint16_t i = EEPROM_BEGIN;
while (i + sizeof(table_t) < EEPROM_END) {
eeprom_read_block(table, (void *)i, sizeof(table_t));
/* Our EEPROM usage is terminated by a table of length zero. */
if (table->len == 0) {
return EEPROM_EOF;
}
/* Table is invalid; it extends past the end of available memory. */
else if (i + table->len >= EEPROM_END) {
return EEPROM_ERROR;
}
/* Found a match (although the checksum may fail...). */
else if (id == table->id) {
return i;
}
else {
i += table->len;
}
}
return EEPROM_EOF;
}
uint16_t storage_end(void) {
table_t table;
uint16_t i = EEPROM_BEGIN;
while (i + sizeof(table_t) < EEPROM_END) {
eeprom_read_block(&table, (void *)i, sizeof(table_t));
/* Found the end of valid tables in the file. */
if (table.len == 0 || i + sizeof(table_t) + table.len >= EEPROM_END) {
break;
} else {
i += table.len;
}
}
return i;
}
bool storage_get(table_t *table) {
uint16_t i;
table_t buf;
i = storage_find(table->id, &buf);
/* There is no table with the desired ID. */
if (i == EEPROM_EOF) {
return false;
}
/* Table extends past the end of available EEPROM. */
else if (i == EEPROM_ERROR) {
ERROR("storage_get", "table intersects end of available memory");
return false;
}
/* Copy the table's data from EEPROM into RAM. */
eeprom_read_block(table, (void *)i, table->len);
/* Verify the table's checksum. */
if (storage_sum(table) != table->sum) {
ERROR("storage_get", "table failed checksum");
return false;
} else {
return true;
}
}
bool storage_set(table_t *table) {
uint16_t end = storage_end();
uint16_t i;
table_t buf;
i = storage_find(table->id, &buf);
table->sum = storage_sum(table);
/* Table extends past the end of available EEPROM. */
if (i == EEPROM_ERROR) {
ERROR("storage_set", "table intersects end of available memory");
return false;
}
/* There is not enough room to append the table to the end of the EEPROM. */
else if (i == EEPROM_EOF && end + table->len >= EEPROM_END) {
ERROR("storage_set", "insufficient memory");
return false;
}
/* Append the table to the end of the EEPROM. */
else if (i == EEPROM_EOF) {
eeprom_write_block(table, (void *)end, table->len);
return true;
}
/* Table in EEPROM has a different structure than the one we're writing. */
else if (table->len != buf.len || table->ver != buf.ver) {
ERROR("storage_set", "incorrect table size or version");
return false;
}
/* Table header is the same, only the data is different. */
else {
table->sum = storage_sum(table);
eeprom_write_block(table, (void *)i, table->len);
return true;
}
}