248 lines
6.4 KiB
C
248 lines
6.4 KiB
C
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/*
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Contiki library for DS18B20 temperature sensor -
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For more details see http://xxx
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Author -
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Author -
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License - GPLv3
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*/
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#include "ds18b20.h"
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/* probe_for_ds18b20 probes for the sensor. Returns 0 on failure, 1 on success */
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/* Assumptions: only one sensor on the "1-wire bus", on port WSN_DS18B20_PORT */
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/* BUG: THIS CODE DOES NOT WORK AS INTENDED! IT RETURNS "1" EVEN WHEN THERE IS NO */
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/* SENSOR CONNECTED. */
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uint8_t
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ds18b20_probe(void)
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{
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uint8_t result = 0;
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/* Reset 1W-bus */
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/* Pull PIN low for 480 microseconds (us) */
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/* Start with setting bit DS18B20_1_PIN to 0 */
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OW_SET_PIN_LOW();
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/* then set direction to OUT by setting DS18B20_1_DDR bit to 1 */
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OW_SET_OUTPUT();
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/* Delay 480 us */
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clock_delay_usec(480);
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/* See if sensor responds. First release the bus and switch to INput mode */
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/* by setting DS18B20_1_DDR bit to 0 */
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OW_SET_INPUT();
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/* Activate internal pull-up by setting pin to HIGH (when in INput mode) */
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/* OW_SET_PIN_HIGH(); */
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/* Wait for the pin to go HIGH for 64 us */
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clock_delay_usec(64);
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/* Now the sensor, if present, pulls the pin LOW for 60-240 us */
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/* Detect 0 on PIND bit DS18B20_1_PIN. Invert the result so a presence (aka a 0) */
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/* sets "result" to 1 (for success) */
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result = !OW_GET_PIN_STATE();
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/* The sensor releases the pin so it goes HIGH after 240 us, add some */
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/* for the signal to stabilize, say 300 usecs to be on the safe side? */
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if(result) {
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clock_delay_usec(300);
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/* Now the bus should be HIGH again */
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result = OW_GET_PIN_STATE();
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}
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return result;
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}
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/* Write 1 or 0 on the bus */
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void
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write_bit(uint8_t bit)
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{
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/* Set pin to 0 */
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OW_SET_OUTPUT();
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OW_SET_PIN_LOW();
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/* Pin should be 0 for at least 1 us */
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clock_delay_usec(2);
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/* If we're writing a 1, let interna pull-up pull the bus high */
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/* within 15 us of setting the bus to low */
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if(bit) {
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/* Internal pull-up is activated by setting direction to IN and the */
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/* setting the pin to HIGH */
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OW_SET_INPUT();
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OW_SET_PIN_HIGH();
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}
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/* OK, now the bus is either LOW, or pulled HIGH by the internal pull-up */
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/* Let this state remain for 60 us, then release the bus */
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clock_delay_usec(60);
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/* Release the bus */
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OW_SET_PIN_HIGH();
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OW_SET_INPUT();
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/* Allow > 1 us between read/write operations */
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clock_delay_usec(2);
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}
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/* */
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/* Read one bit of information from the bus, and return it as 1 or 0 */
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/* */
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uint8_t
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read_bit(void)
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{
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uint8_t bit = 0;
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/* Set pin to 0 */
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OW_SET_OUTPUT();
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OW_SET_PIN_LOW();
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/* Pin should be 0 for at least 1 us */
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clock_delay_usec(2);
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/* Now read the bus, start by setting in/out direction and activating internal */
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/* pull-up resistor */
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OW_SET_INPUT();
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OW_SET_PIN_HIGH();
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/* ds18b20 either keeps the pin down or releases the bus and the */
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/* bus then goes high because of the interna pull-up resistor */
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/* Check whichever happens before 15 us has passed */
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clock_delay_usec(15 - 2 - 1);
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bit = OW_GET_PIN_STATE();
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/* The complete read cycle must last at least 60 us. We have now spent */
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/* about 14-15 us in delays, so add another delay to reach >= 60 us */
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clock_delay_usec(50);
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/* Release bus */
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OW_SET_PIN_HIGH();
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OW_SET_INPUT();
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/* Allow > 1 us between read/write operations */
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clock_delay_usec(2);
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return bit ? 1 : 0;
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}
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/* */
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/* Read one byte of information. A byte is read least significant bit first */
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/* */
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uint8_t
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read_byte(void)
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{
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uint8_t result = 0;
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uint8_t bit;
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int i;
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for(i = 0; i < 8; i++) {
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bit = read_bit();
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result += (bit << i);
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}
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return result;
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}
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/* */
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/* Write one byte of information. A byte is written least significant bit first */
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/* */
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void
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write_byte(uint8_t byte)
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{
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int i;
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for(i = 0; i < 8; i++) {
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write_bit((byte >> i) & 1);
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}
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}
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/* */
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/* ds18b20_get_temp returns the temperature in "temp" (in degrees celsius) */
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/* Returns 0 on failure (and then "temp" is left unchanged */
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/* Returns 1 on success, and sets temp */
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/* */
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uint8_t
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ds18b20_get_temp(float *temp)
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{
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uint8_t result = 0;
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/* Reset bus by probing. Probe returns 1 on success/presence of sensor */
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if(ds18b20_probe()) {
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/* write command "skip rom" since we only have one sensor on the wire! */
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write_byte(DS18B20_COMMAND_SKIP_ROM);
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/* write command to start measurement */
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write_byte(DS18B20_COMMAND_START_CONVERSION);
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/* Wait for conversion to complete */
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/* Conversion is 12-bit by default. */
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/* Since we have external power to the sensor (ie not in "parasitic power" mode) */
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/* the bus is held LOW by the sensor while the conversion is going on, and then HIGH */
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/* when conversion is finished. */
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OW_SET_INPUT();
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int count = 0;
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while(!OW_GET_PIN_STATE()) {
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clock_delay_msec(10);
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count++;
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/* Longest conversion time is 750 ms (12-bit resolution) */
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/* So if count > 80 (for a little margin!), we return -274.0 */
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/* which indicates failure to read the temperature. */
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if(count > 80) {
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return 0;
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}
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}
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/* The result is stored in the "scratch pad", a 9 byte memory block. */
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/* The first two bytes are the conversion result. Reading the scratch pad */
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/* can be terminated by sending a reset signal (but we read all 9 bytes) */
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(void)ds18b20_probe();
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write_byte(DS18B20_COMMAND_SKIP_ROM);
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write_byte(DS18B20_COMMAND_READ_SCRATCH_PAD);
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uint8_t i, sp_arr[9];
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for(i = 0; i < 9; i++) {
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sp_arr[i] = read_byte();
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}
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/* Check CRC, if mismatch, return 0 (failure to read temperature) */
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uint8_t crc_cal = crc8_ds18b20(sp_arr, 8);
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if(crc_cal != sp_arr[8]) {
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return 0;
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}
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/* OK, now decode what the temperature reading is. This code assumes 12-bit resolution, */
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/* so this must be modified if the code is modified to use any other resolution! */
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int16_t temp_res;
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uint8_t temp_lsb = sp_arr[0];
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uint8_t temp_msb = sp_arr[1];
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temp_res = (int16_t)temp_msb << 8 | temp_lsb;
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*temp = (float)temp_res * 0.0625;
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result = 1;
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}
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return result;
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}
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/* */
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/* crc8 algorithm for ds18b20 */
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/* http://www.miscel.dk/MiscEl/CRCcalculations.html */
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/* */
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uint8_t
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crc8_ds18b20(uint8_t *buf, uint8_t buf_len)
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{
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uint8_t result = 0;
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uint8_t i, b;
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for(i = 0; i < buf_len; i++) {
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result = result ^ buf[i];
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for(b = 1; b < 9; b++) {
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if(result & 0x1) {
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result = (result >> 1) ^ 0x8C;
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} else {
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result = result >> 1;
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}
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}
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}
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return result;
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}
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