[I2C] Timing can be hard coded

To avoid time spent to compute the I2C timing, it can be defined in
the variant.h or build_opt.h or hal_conf_extra.h with:

  * I2C_TIMING_SM for Standard Mode (100kHz)
  * I2C_TIMING_FM for Fast Mode (400kHz)
  * I2C_TIMING_FMP for Fast Mode Plus (1000kHz)

Example for a STM32F0xx using HSI clock as I2C clock source:

#define I2C_TIMING_SM           0x00201D2B
#define I2C_TIMING_FM           0x0010020A

Signed-off-by: Frederic.Pillon <[email protected]>

Author: fpistm

cores/arduino/stm32/twi.c

@@ -476,13 +476,25 @@ static uint32_t i2c_getTiming(i2c_t *obj, uint32_t frequency)
     switch (i2c_speed) {
       default:
       case 100000:
+#ifdef I2C_TIMING_SM
+        ret = I2C_TIMING_SM;
+#else
         ret = i2c_computeTiming(i2c_getClkFreq(obj->i2c), I2C_SPEED_FREQ_STANDARD);
+#endif
         break;
       case 400000:
+#ifdef I2C_TIMING_FM
+        ret = I2C_TIMING_FM;
+#else
         ret = i2c_computeTiming(i2c_getClkFreq(obj->i2c), I2C_SPEED_FREQ_FAST);
+#endif
         break;
       case 1000000:
+#ifdef I2C_TIMING_FMP
+        ret = I2C_TIMING_FMP;
+#else
         ret = i2c_computeTiming(i2c_getClkFreq(obj->i2c), I2C_SPEED_FREQ_FAST_PLUS);
+#endif
         break;
     }
   }

variants/board_template/variant.h

@@ -113,6 +113,14 @@ extern "C" {
 //#define PIN_WIRE_SDA            14 // Default for Arduino connector compatibility
 //#define PIN_WIRE_SCL            15 // Default for Arduino connector compatibility
 
+// I2C timing definitions (optional), avoid time spent to compute if defined
+// * I2C_TIMING_SM for Standard Mode (100kHz)
+// * I2C_TIMING_FM for Fast Mode (400kHz)
+// * I2C_TIMING_FMP for Fast Mode Plus (1000kHz)
+//#define I2C_TIMING_SM           0x00000000
+//#define I2C_TIMING_FM           0x00000000
+//#define I2C_TIMING_FMP          0x00000000
+
 // Timer Definitions (optional)
 //Do not use timer used by PWM pins when possible. See PinMap_PWM in PeripheralPins.c
 #define TIMER_TONE              TIMx