lib/ds18b20.c

   1 /*
   2  *      Interface to DS18B20 Temperature Sensors
   3  *
   4  *      (c) 2019 Martin Mareš <mj@ucw.cz>
   5  */
   6
   7 #include "util.h"
   8 #include "ds18b20.h"
   9 #include "ext-timer.h"
  10
  11 #include <libopencm3/cm3/cortex.h>
  12 #include <libopencm3/stm32/dma.h>
  13 #include <libopencm3/stm32/gpio.h>
  14 #include <libopencm3/stm32/rcc.h>
  15 #include <string.h>
  16
  17 /*** Configuration ***/
  18
  19 // You should set the following parameters in config.h
  20
  21 // #define DS_TIMER TIM3
  22 // #define DS_GPIO GPIOA
  23 // #define DS_PIN GPIO7
  24 // #define DS_DMA DMA1
  25 // #define DS_DMA_CH 6
  26
  27 // #undef DS_DEBUG
  28 // #undef DS_DEBUG2
  29
  30 // Maximum number of supported sensors
  31 // #define DS_NUM_SENSORS 8
  32
  33 #ifdef DS_DEBUG
  34 #define DEBUG debug_printf
  35 #else
  36 #define DEBUG(xxx, ...) do { } while (0)
  37 #endif
  38
  39 #ifdef DS_DEBUG2
  40 #define DEBUG2 debug_printf
  41 #else
  42 #define DEBUG2(xxx, ...) do { } while (0)
  43 #endif
  44
  45 static volatile u32 ds_dma_buffer;
  46
  47 static bool ds_reset(void)
  48 {
  49         DEBUG2("DS18B20: Reset\n");
  50         timer_disable_counter(DS_TIMER);
  51         timer_one_shot_mode(DS_TIMER);
  52
  53         // DMA for reading pin state
  54         ds_dma_buffer = 0xdeadbeef;
  55         dma_set_memory_address(DS_DMA, DS_DMA_CH, (u32) &ds_dma_buffer);
  56         dma_set_peripheral_address(DS_DMA, DS_DMA_CH, (u32) &GPIO_IDR(DS_GPIO));
  57         dma_set_number_of_data(DS_DMA, DS_DMA_CH, 1);
  58         dma_enable_channel(DS_DMA, DS_DMA_CH);
  59
  60         // CC1 is used to drive the DMA (read line state at specified time)
  61         timer_disable_oc_output(DS_TIMER, TIM_OC1);
  62         timer_set_oc_mode(DS_TIMER, TIM_OC1, TIM_OCM_FROZEN);
  63         timer_set_oc_value(DS_TIMER, TIM_OC1, 560);
  64         timer_set_dma_on_compare_event(DS_TIMER);
  65         timer_enable_dma_cc1(DS_TIMER);
  66
  67         // CC2 is used to generate pulses (return line to idle state at specified time)
  68         timer_set_oc_mode(DS_TIMER, TIM_OC2, TIM_OCM_FORCE_HIGH);
  69         timer_enable_oc_output(DS_TIMER, TIM_OC2);
  70         timer_set_oc_value(DS_TIMER, TIM_OC2, 480);
  71         timer_set_oc_polarity_low(DS_TIMER, TIM_OC2);
  72
  73         // Set timer period to the length of the whole transaction (1 ms)
  74         timer_set_period(DS_TIMER, 999);
  75
  76         // Pull line down and start timer
  77         cm_disable_interrupts();
  78         timer_enable_counter(DS_TIMER);
  79         timer_set_oc_mode(DS_TIMER, TIM_OC2, TIM_OCM_INACTIVE);
  80         cm_enable_interrupts();
  81
  82         // Wait until the timer expires
  83         while (timer_is_counter_enabled(DS_TIMER))
  84                 ;
  85         // Counter is automatically disabled at the end of cycle
  86
  87         // Disable DMA
  88         timer_disable_dma_cc1(DS_TIMER);
  89         dma_disable_channel(DS_DMA, DS_DMA_CH);
  90
  91         DEBUG2("Init DMA: %08x [%u] (%u remains)\n",
  92                ds_dma_buffer,
  93                !!(ds_dma_buffer & DS_PIN),
  94                dma_get_number_of_data(DS_DMA, DS_DMA_CH));
  95
  96         // Did the device respond?
  97         if (ds_dma_buffer & DS_PIN) {
  98                 DEBUG("DS18B20: Initialization failed\n");
  99                 return 0;
 100         } else
 101                 return 1;
 102 }
 103
 104 static void ds_send_bit(bool bit)
 105 {
 106         timer_set_period(DS_TIMER, 99);                         // Each write slot takes 100 μs
 107         timer_set_oc_mode(DS_TIMER, TIM_OC2, TIM_OCM_FORCE_HIGH);
 108         timer_set_oc_value(DS_TIMER, TIM_OC2, (bit ? 3 : 89));  // 1: 3μs pulse, 0: 89μs pulse
 109         cm_disable_interrupts();
 110         // XXX: On STM32F1, we must configure the OC channel _after_ we enable the counter,
 111         // otherwise OC triggers immediately. Reasons?
 112         timer_enable_counter(DS_TIMER);
 113         timer_set_oc_mode(DS_TIMER, TIM_OC2, TIM_OCM_INACTIVE);
 114         cm_enable_interrupts();
 115         while (timer_is_counter_enabled(DS_TIMER))
 116                 ;
 117 }
 118
 119 static void ds_send_byte(byte b)
 120 {
 121         DEBUG2("DS write: %02x\n", b);
 122         for (uint m = 1; m < 0x100; m <<= 1)
 123                 ds_send_bit(b & m);
 124 }
 125
 126 static bool ds_recv_bit(void)
 127 {
 128         timer_set_period(DS_TIMER, 79);                 // Each read slot takes 80μs
 129         timer_set_oc_value(DS_TIMER, TIM_OC2, 2);       // Generate 2μs pulse to start read slot
 130         timer_set_oc_value(DS_TIMER, TIM_OC1, 8);       // Sample data 8μs after start of slot
 131         timer_enable_dma_cc1(DS_TIMER);
 132
 133         ds_dma_buffer = 0xdeadbeef;
 134         dma_set_number_of_data(DS_DMA, DS_DMA_CH, 1);
 135         dma_enable_channel(DS_DMA, DS_DMA_CH);
 136         timer_set_oc_mode(DS_TIMER, TIM_OC2, TIM_OCM_FORCE_HIGH);
 137         cm_disable_interrupts();
 138         timer_enable_counter(DS_TIMER);
 139         timer_set_oc_mode(DS_TIMER, TIM_OC2, TIM_OCM_INACTIVE);
 140         cm_enable_interrupts();
 141         while (timer_is_counter_enabled(DS_TIMER))
 142                 ;
 143         // DEBUG2("XXX %08x\n", ds_dma_buffer);
 144         bool out = ds_dma_buffer & DS_PIN;
 145         dma_disable_channel(DS_DMA, DS_DMA_CH);
 146
 147         timer_disable_dma_cc1(DS_TIMER);
 148
 149         return out;
 150 }
 151
 152 static byte ds_recv_byte(void)
 153 {
 154         uint out = 0;
 155         for (uint m = 1; m < 0x100; m <<= 1) {
 156                 if (ds_recv_bit())
 157                         out |= m;
 158         }
 159
 160         DEBUG2("DS read: %02x\n", out);
 161         return out;
 162 }
 163
 164 static byte ds_buf[10];
 165
 166 static byte ds_crc_block(uint n)
 167 {
 168         /// XXX: This might be worth optimizing
 169         uint crc = 0;
 170
 171         for (uint i = 0; i < n; i++) {
 172                 byte b = ds_buf[i];
 173                 for (uint j = 0; j < 8; j++) {
 174                         uint k = (b & 1) ^ (crc >> 7);
 175                         crc = (crc << 1) & 0xff;
 176                         if (k)
 177                                 crc ^= 0x31;
 178                         b >>= 1;
 179                 }
 180         }
 181
 182         return crc;
 183 }
 184
 185 static bool ds_recv_block(uint n)
 186 {
 187         for (uint i = 0; i < n; i++)
 188                 ds_buf[i] = ds_recv_byte();
 189
 190         byte crc = ds_crc_block(n);
 191         if (crc) {
 192                 DEBUG("DS18B20: Invalid CRC %02x\n", crc);
 193                 return 0;
 194         }
 195         return 1;
 196 }
 197
 198 struct ds_sensor ds_sensors[DS_NUM_SENSORS];
 199
 200 #if DS_NUM_SENSORS == 1
 201
 202 static void ds_enumerate(void)
 203 {
 204         if (!ds_reset())
 205                 return;
 206
 207         ds_send_byte(0x33);     // READ_ROM
 208         if (!ds_recv_block(8))
 209                 return;
 210
 211         DEBUG("DS18B20: Found sensor ");
 212         for (uint i = 0; i < 8; i++) {
 213                 DEBUG("%02x", ds_buf[i]);
 214                 ds_sensors[0].address[i] = ds_buf[i];
 215         }
 216         DEBUG("\n");
 217 }
 218
 219 #else
 220
 221 static void ds_enumerate(void)
 222 {
 223         /*
 224          *  The enumeration algorithm roughly follows the one described in the
 225          *  Book of iButton Standards (Maxim Integrated Application Note 937).
 226          *
 227          *  It simulates depth-first search on the trie of all device IDs.
 228          *  In each pass, it walks the trie from the root and recognizes branching nodes.
 229          *
 230          *  The old_choice variable remembers the deepest left branch taken in the
 231          *  previous pass, new_choice is the same for the current pass.
 232          */
 233
 234         DEBUG("DS18B20: Enumerate\n");
 235
 236         uint num_sensors = 0;
 237         byte *addr = ds_buf;
 238         byte old_choice = 0;
 239
 240         for (;;) {
 241                 if (!ds_reset()) {
 242                         DEBUG("DS18B20: Enumeration found no sensor\n");
 243                         return;
 244                 }
 245
 246                 ds_send_byte(0xf0);     // SEARCH_ROM
 247                 byte new_choice = 0;
 248                 for (byte i=0; i<64; i++) {
 249                         bool have_one = ds_recv_bit();
 250                         bool have_zero = ds_recv_bit();
 251                         bool old_bit = addr[i/8] & (1U << (i%8));
 252                         bool new_bit;
 253                         switch (2*have_one + have_zero) {
 254                                 case 3:
 255                                         // This should not happen
 256                                         DEBUG("DS18B20: Enumeration failed\n");
 257                                         return;
 258                                 case 1:
 259                                         // Only 0
 260                                         new_bit = 0;
 261                                         break;
 262                                 case 2:
 263                                         // Only 1
 264                                         new_bit = 1;
 265                                         break;
 266                                 default:
 267                                         // Both
 268                                         if (i == old_choice)
 269                                                 new_bit = 1;
 270                                         else if (i > old_choice) {
 271                                                 new_bit = 0;
 272                                                 new_choice = i;
 273                                         } else {
 274                                                 new_bit = old_bit;
 275                                                 if (!new_bit)
 276                                                         new_choice = i;
 277                                         }
 278                         }
 279                         if (new_bit)
 280                                 addr[i/8] |= 1U << (i%8);
 281                         else
 282                                 addr[i/8] &= ~(1U << (i%8));
 283                         ds_send_bit(new_bit);
 284                 }
 285
 286                 if (num_sensors >= DS_NUM_SENSORS) {
 287                         DEBUG("DS18B20: Too many sensors\n");
 288                         return;
 289                 }
 290
 291                 DEBUG("DS18B20: Found sensor #%u: ", num_sensors);
 292                 for (byte i=0; i<8; i++)
 293                         DEBUG("%02x", addr[i]);
 294                 if (ds_crc_block(8)) {
 295                         DEBUG(" - invalid CRC!\n");
 296                 } else if (ds_buf[0] == 0x28) {
 297                         DEBUG("\n");
 298                         memcpy(ds_sensors[num_sensors].address, ds_buf, 8);
 299                         num_sensors++;
 300                 } else {
 301                         DEBUG(" - wrong type\n");
 302                 }
 303
 304                 old_choice = new_choice;
 305                 if (!old_choice)
 306                         break;
 307         }
 308 }
 309
 310 #endif
 311
 312 void ds_init(void)
 313 {
 314         DEBUG("DS18B20: Init\n");
 315
 316         for (uint i = 0; i < DS_NUM_SENSORS; i++) {
 317                 memset(ds_sensors[i].address, 0, 8);
 318                 ds_sensors[i].current_temp = DS_TEMP_UNKNOWN;
 319         }
 320
 321         dma_set_read_from_peripheral(DS_DMA, DS_DMA_CH);
 322         dma_set_priority(DS_DMA, DS_DMA_CH, DMA_CCR_PL_VERY_HIGH);
 323         dma_disable_peripheral_increment_mode(DS_DMA, DS_DMA_CH);
 324         dma_enable_memory_increment_mode(DS_DMA, DS_DMA_CH);
 325         dma_set_peripheral_size(DS_DMA, DS_DMA_CH, DMA_CCR_PSIZE_16BIT);
 326         dma_set_memory_size(DS_DMA, DS_DMA_CH, DMA_CCR_MSIZE_16BIT);
 327
 328         timer_set_prescaler(DS_TIMER, CPU_CLOCK_MHZ - 1);       // 1 tick = 1 μs
 329         timer_set_mode(DS_TIMER, TIM_CR1_CKD_CK_INT, TIM_CR1_CMS_EDGE, TIM_CR1_DIR_UP);
 330         timer_disable_preload(DS_TIMER);
 331
 332         gpio_set_mode(DS_GPIO, GPIO_MODE_OUTPUT_50_MHZ, GPIO_CNF_OUTPUT_ALTFN_OPENDRAIN, DS_PIN);
 333
 334         ds_enumerate();
 335
 336         // FIXME: Configure precision?
 337 }
 338
 339 #if DS_NUM_SENSORS == 1
 340 #define ds_current_id 0
 341 #else
 342         static byte ds_current_id;
 343 #endif
 344
 345 static bool ds_activate(void)
 346 {
 347         if (!ds_reset()) {
 348                 DEBUG("DS18B20: Reset failed\n");
 349                 return false;
 350         }
 351 #if DS_NUM_SENSORS == 1
 352         ds_send_byte(0xcc);     // SKIP_ROM
 353 #else
 354         ds_send_byte(0x55);     // MATCH_ROM
 355         for (uint i = 0; i < 8; i++)
 356                 ds_send_byte(ds_sensors[ds_current_id].address[i]);
 357 #endif
 358         return true;
 359 }
 360
 361 void ds_step(void)
 362 {
 363         static byte ds_running;
 364         static byte ds_timeout;
 365
 366         if (!ds_running) {
 367                 // Start measurement
 368 #if DS_NUM_SENSORS != 1
 369                 uint maxn = DS_NUM_SENSORS;
 370                 do {
 371                         if (!maxn--)
 372                                 return;
 373                         ds_current_id++;
 374                         if (ds_current_id >= DS_NUM_SENSORS) {
 375                                 ds_current_id = 0;
 376                         }
 377                 } while (!ds_sensors[ds_current_id].address[0]);
 378 #endif
 379                 if (!ds_activate()) {
 380                         ds_sensors[ds_current_id].current_temp = DS_TEMP_UNKNOWN;
 381                         return;
 382                 }
 383                 ds_send_byte(0x44);     // CONVERT_T
 384                 ds_running = 1;
 385                 ds_timeout = 255;
 386         } else {
 387                 // Still running?
 388                 if (!ds_recv_bit()) {
 389                         if (!ds_timeout--) {
 390                                 DEBUG("DS18B20 #%u: Timeout\n", ds_current_id);
 391                                 ds_sensors[ds_current_id].current_temp = DS_TEMP_UNKNOWN;
 392                                 ds_running = 0;
 393                         }
 394                         return;
 395                 }
 396                 ds_running = 0;
 397
 398                 // Read scratch pad
 399                 if (!ds_activate())
 400                         return;
 401                 ds_send_byte(0xbe);     // READ_SCRATCHPAD
 402                 if (!ds_recv_block(9)) {
 403                         ds_sensors[ds_current_id].current_temp = DS_TEMP_UNKNOWN;
 404                         return;
 405                 }
 406                 int t = (int16_t) (ds_buf[0] | (ds_buf[1] << 8));
 407                 t = t * 1000 / 16;
 408
 409                 DEBUG("DS18B20 #%u: %d.%03d degC\n", ds_current_id, t / 1000, t % 1000);
 410                 ds_sensors[ds_current_id].current_temp = t;
 411         }
 412 }