[I2C] Limit iteration number to compute timing

Computing all timing values consumes huge time. By default only the first 8 valid timing will be computed. It can be redefined thanks the variant.h or build_opt.h or hal_conf_extra.h using: I2C_VALID_TIMING_NBR Higher number ensure lowest clock error but require more time to compute. Signed-off-by: Frederic.Pillon <frederic.pillon@st.com>

Author: fpistm

cores/arduino/stm32/twi.c

@@ -59,6 +59,9 @@ extern "C" {
 #endif
 
 #ifdef I2C_TIMING
+#ifndef I2C_VALID_TIMING_NBR
+#define I2C_VALID_TIMING_NBR 8U
+#endif
 #define I2C_SPEED_FREQ_STANDARD 0U /* 100 kHz */
 #define I2C_SPEED_FREQ_FAST 1U /* 400 kHz */
 #define I2C_SPEED_FREQ_FAST_PLUS 2U /* 1 MHz */
@@ -337,6 +340,7 @@ valid config.
 static uint32_t i2c_computeTiming(uint32_t clkSrcFreq, uint32_t i2c_speed)
 {
  uint32_t ret = 0xFFFFFFFFU;
+ uint32_t valid_timing_nbr = 0;
  uint32_t ti2cclk;
  uint32_t ti2cspeed;
  uint32_t prev_error;
@@ -399,6 +403,10 @@ static uint32_t i2c_computeTiming(uint32_t clkSrcFreq, uint32_t i2c_speed)
  if ((tsdadel >= (uint32_t)tsdadel_min) && (tsdadel <=
  (uint32_t)tsdadel_max)) {
  if (presc != prev_presc) {
+ valid_timing_nbr ++;
+ if (valid_timing_nbr >= I2C_VALID_TIMING_NBR) {
+ return ret;
+ }
  /* tPRESC = (PRESC+1) x tI2CCLK*/
  uint32_t tpresc = (presc + 1U) * ti2cclk;
  for (scll = 0; scll < I2C_SCLL_MAX; scll++) {