1-Wire bus search algorithm, new C implementation
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//
// Created by MightyPork on 2018/02/01.
// MIT license
//
#include <stdlib.h>
#include <stdint.h>
#include <stdbool.h>
#include <string.h>
#include "ow_search.h"
// -------- CHECKSUM --------
static inline uint8_t crc8_bits(uint8_t data)
{
uint8_t crc = 0;
if(data & 1) crc ^= 0x5e;
if(data & 2) crc ^= 0xbc;
if(data & 4) crc ^= 0x61;
if(data & 8) crc ^= 0xc2;
if(data & 0x10) crc ^= 0x9d;
if(data & 0x20) crc ^= 0x23;
if(data & 0x40) crc ^= 0x46;
if(data & 0x80) crc ^= 0x8c;
return crc;
}
static uint8_t crc8_add(uint8_t cksum, uint8_t byte)
{
return crc8_bits(byte ^ cksum);
}
uint8_t ow_checksum(const uint8_t *buff, uint16_t len)
{
uint8_t cksum = 0;
for(uint16_t i = 0; i < len; i++) {
cksum = crc8_add(cksum, buff[i]);
}
return cksum;
}
// -----------------------------
void ow_search_init(struct ow_search_state *state, uint8_t command, bool test_checksums)
{
state->prev_last_fork = 64;
memset(state->prev_code, 0, 8);
state->status = OW_SEARCH_MORE;
state->command = command;
state->first = true;
state->test_checksums = test_checksums;
}
uint16_t ow_search_run(struct ow_search_state *state, ow_romcode_t *codes, uint16_t capacity)
{
if (state->status != OW_SEARCH_MORE) return 0;
uint16_t found_devices = 0;
while (found_devices < capacity) {
uint8_t index = 0;
ow_romcode_t code = {};
int8_t last_fork = -1;
// Start a new transaction. Devices respond to reset
if (!ow_reset()) {
state->status = OW_SEARCH_FAILED;
goto done;
}
// Send the search command (SEARCH_ROM, SEARCH_ALARM)
ow_write_u8(state->command);
uint8_t *code_byte = &code[0];
bool p, n;
while (index != 64) {
// Read a bit and its complement
p = ow_read_bit();
n = ow_read_bit();
if (!p && !n) {
// A fork: there are devices on the bus with different bit value
// (the bus is open-drain, in both cases one device pulls it low)
if ((found_devices > 0 || !state->first) && index < state->prev_last_fork) {
// earlier than the last fork, take the same turn as before
p = ow_code_getbit(state->prev_code, index);
if (!p) last_fork = index; // remember for future runs, 1 not explored yet
}
else if (index == state->prev_last_fork) {
p = 1; // both forks are now exhausted
}
else { // a new fork
last_fork = index;
}
}
else if (p && n) {
// No devices left connected - this doesn't normally happen
state->status = OW_SEARCH_FAILED;
goto done;
}
// All devices have a matching bit here, or it was resolved in a fork
if (p) *code_byte |= (1 << (index & 7));
ow_write_bit(p);
index++;
if((index & 7) == 0) {
code_byte++;
}
}
memcpy(state->prev_code, code, 8);
if (!state->test_checksums || 0 == ow_checksum(code, 8)) {
// Record a found address
memcpy(codes[found_devices], code, 8);
found_devices++;
}
// Stop condition
if (last_fork == -1) {
state->status = OW_SEARCH_DONE;
goto done;
}
state->prev_last_fork = last_fork;
}
done:
state->first = false;
return found_devices;
}