169 lines
4.4 KiB
C
169 lines
4.4 KiB
C
/* ds18b20.c -- 1-Wire digital thermometer */
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/* Copyright (c) 2020 Renaud Fivet */
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#include "ds18b20.h" /* implements DS18B20 API */
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#include "system.h" /* gpioa_(), usleep() */
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#define DIO 13
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#define input() gpioa_input( DIO)
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#define output() gpioa_output( DIO)
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#define bread() gpioa_read( DIO)
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#define MAX_RETRIES 999
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#define wait_level( lvl) \
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retries = MAX_RETRIES ; \
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while( bread() != lvl) \
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if( retries-- == 0) \
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return DS18B20_FAIL_TOUT
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void ds18b20_init( void) {
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input() ; /* Wire floating, HIGH by pull-up */
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}
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static ds18b20_retv_t initialization( void) {
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/* Reset */
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output() ; /* Wire LOW */
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usleep( 480) ;
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input() ; /* Wire floating, HIGH by pull-up */
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/* Presence */
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int retries ;
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wait_level( HIGH) ; /* Pull-up LOW -> HIGH, T1 */
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wait_level( LOW) ; /* DS18B20 asserts line to LOW, T2, T2 - T1 = 15~60us */
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wait_level( HIGH) ; /* DS18B20 releases lines, Pull-up LOW -> HIGH, T3
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** T3 - T2 = 60~240us */
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usleep( 405) ; /* 480 = 405 + 15 + 60 */
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return DS18B20_SUCCESS ;
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}
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static void write( unsigned char uc) {
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/* Transmit byte, least significant bit first */
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for( unsigned char curbit = 1 ; curbit ; curbit <<= 1) {
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/* Transmit a bit takes 60us + 1us between transmit */
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/* Write 1: <15us LOW */
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/* Write 0: 60us LOW */
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unsigned t = uc & curbit ? 13 : 60 ;
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output() ; /* Wire LOW */
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usleep( t) ;
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input() ; /* Wire floating, HIGH by pull-up */
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usleep( 61 - t) ;
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}
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}
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static iolvl_t poll( void) {
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output() ; /* Wire LOW */
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usleep( 1) ;
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input() ; /* Wire floating, HIGH by pull-up */
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usleep( 5) ;
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iolvl_t bit = bread() ;
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usleep( 55) ;
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return bit ;
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}
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static unsigned char read( unsigned char *p, int size) {
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unsigned char crc = 0 ;
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while( size--) {
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/* Receive byte, least significant bit first */
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unsigned char uc = 0 ;
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for( unsigned char curbit = 1 ; curbit ; curbit <<= 1) {
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/* read bit */
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int v = poll() ;
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if( v)
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uc |= curbit ;
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/* update CRC */
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v ^= crc ;
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crc >>= 1 ;
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if( v & 1)
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crc ^= 0x119 >> 1 ; /* reverse POLY = x^8 + x^5 + x^4 + 1 */
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}
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/* store byte */
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*p++ = uc ;
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}
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return crc ;
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}
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static ds18b20_retv_t read_scratchpad( unsigned char scratchpad[]) {
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ds18b20_retv_t ret = initialization() ;
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if( ret != DS18B20_SUCCESS)
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return ret ;
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write( 0xCC) ; /* Skip ROM */
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write( 0xBE) ; /* Read Scratchpad */
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return read( scratchpad, 9) ? DS18B20_FAIL_CRC : DS18B20_SUCCESS ;
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}
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ds18b20_retv_t ds18b20_convert( void) {
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ds18b20_retv_t ret ;
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ret = initialization() ;
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if( ret != DS18B20_SUCCESS)
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return ret ;
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write( 0xCC) ; /* Skip ROM */
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write( 0x44) ; /* Convert T */
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return DS18B20_SUCCESS ;
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}
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ds18b20_retv_t ds18b20_fetch( short *deciCtemp) { /* -550~1250 = -55.0~125.0 C */
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ds18b20_retv_t ret ;
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unsigned char vals[ 9] ; /* scratchpad */
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ret = read_scratchpad( vals) ;
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if( ret != DS18B20_SUCCESS)
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return ret ;
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*deciCtemp = *((short *) vals) * 10 / 16 ;
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return DS18B20_SUCCESS ;
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}
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ds18b20_retv_t ds18b20_read( short *deciCtemp) { /* -550~1250 = -55.0~125.0 C */
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ds18b20_retv_t ret ;
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ret = ds18b20_convert() ;
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if( ret != DS18B20_SUCCESS)
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return ret ;
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do
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usleep( 4000) ;
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while( poll() == LOW) ; /* up to 93.75ms for 9 bits, 750ms for 12 bits */
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return ds18b20_fetch( deciCtemp) ;
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}
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ds18b20_retv_t ds18b20_resolution( unsigned res) { /* 9..12 bits */
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ds18b20_retv_t ret ;
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unsigned char vals[ 9] ; /* scratchpad */
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unsigned char curres ;
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/* read scratchpad */
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ret = read_scratchpad( vals) ;
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if( ret != DS18B20_SUCCESS)
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return ret ;
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/* update resolution if current value is different than requested */
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res = (res - 9) & 3 ;
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curres = vals[ 4] >> 5 ;
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if( curres != res) {
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vals[ 4] = (vals[ 4] & 0x1F) | (res << 5) ;
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ret = initialization() ;
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if( ret != DS18B20_SUCCESS)
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return ret ;
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write( 0xCC) ; /* Skip ROM */
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write( 0x4E) ; /* Write Scratchpad */
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write( vals[ 2]) ;
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write( vals[ 3]) ;
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write( vals[ 4]) ;
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}
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return DS18B20_SUCCESS ;
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}
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/* end of ds18b20.c */
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