Как рассчитать время i2c для stm32l0

TL; DR: RM0377 Справочное руководство "Ультра-маломощный STM32L0x1 Advanced Arm®-based 32-bit MCU », стр. 614 содержит примеры.

Примечание: я еще не работал с I2C. Все нижеследующее основано на документации.

1. Руководство пользователя UM1749 "Описание STM32L0 HAL и нижнего уровня. водители » (стр. 233):

   uint32_t I2C_InitTypeDef::Timing Specifies the I2C_TIMINGR_register value. This parameter calculated by referring to I2C initialization section in Reference manual

2. RM0377 Справочное руководство "Ультра-маломощный STM32L0x1 Advanced Arm®-based 32-bit MCU » (стр.641):

   Timing register (I2C_TIMINGR)

   (...)

   PRESC[3:0] : Timing prescaler

   This field is used to prescale I2CCLK in order to generate the clock period t_PRESC used for data setup and hold counters (refer to I2C timings on page 587 ) and for SCL high and low level counters (refer to I2C master initialization on page 602 ).

   t_PRESC = (PRESC+1) x t_I2CCLK

   SCLDEL[3:0] : Data setup time This field is used to generate a delay t_SCLDEL between SDA edge and SCL rising edge. In master mode and in slave mode with NOSTRETCH = 0, the SCL line is stretched low during t_SCLDEL.

   t_SCLDEL = (SCLDEL+1) x t_PRESC

   Note: t_SCLDEL is used to generate t_SU:DAT timing.

   SDADEL[3:0] : Data hold time This field is used to generate the delay t_SDADEL between SCL falling edge and SDA edge. In master mode and in slave mode with NOSTRETCH = 0, the SCL line is stretched low during t_SDADEL.

   t_SDADEL = SDADEL x t_PRESC

   Note: SDADEL is used to generate t_HD:DAT timing.

   SCLH[7:0] : SCL high period (master mode) This field is used to generate the SCL high period in master mode.

   t_SCLH = (SCLH+1) x t_PRESC

   Note: SCLH is also used to generate t_SU:STO and t_HD:STA timing.

   SCLL[7:0] : SCL low period (master mode) This field is used to generate the SCL low period in master mode.

   t_SCLL = (SCLL+1) x t_PRESC

   Note: SCLL is also used to generate t_BUF and t_SU:STA timings.

   Более подробную информацию о предделителях можно найти в параграфах о таймерах. (стр. 433).

3. RM0377 (стр. 581):

   The interface is connected to the I2C bus by a data pin (SDA) and by a clock pin (SCL). It can be connected with a standard (up to 100 kHz), Fast-mode (up to 400 kHz) or Fast-mode Plus (up to 1MHz) I2C bus.

   Таким образом, для связи часы I2C должны иметь соответствующую частоту.

4. RM0377 (стр. 583):

   This independent clock source can be selected from the following three clock sources:

   • PCLK1: APB1 clock (default value)
   • HSI16: internal 16 MHz RC oscillator
   • SYSCLK: system clock Refer to Section 7: Reset and clock control (RCC) for more details.

5. RM0377 (стр. 604):

6. RM0377 (стр. 602):

   t_SCL = t_SYNC1 + t_SYNC2 + {[(SCLH+1) + (SCLL+1)] x (PRESC+1) x t_I2CCLK}

   The duration of t_SYNC1 depends on these parameters:

   • SCL falling slope
   • When enabled, input delay induced by the analog filter.
   • When enabled, input delay induced by the digital filter: DNF x t_I2CCLK
   • Delay due to SCL synchronization with I2CCLK clock (2 to 3 I2CCLK periods)

   The duration of t_SYNC2 depends on these parameters:

   • SCL rising slope
   • When enabled, input delay induced by the analog filter.
   • When enabled, input delay induced by the digital filter: DNF x t_I2CCLK
   • Delay due to SCL synchronization with I2CCLK clock (2 to 3 I2CCLK periods)

7. BME280 Лист данных (стр.30):

   All modes (standard, fast, high speed) are supported.

Собирать все это: на основе тактовой частоты I2C и скорости, которую вы хотите использовать, вам необходимо выбрать такие значения PRESC, SCLDEL, SDADEL, SCLH, SCLL, которые соответствуют I2C-SMBUS specification clock timings, используя формулу t_SCL = t_SYNC1 + t_SYNC2 + {[(SCLH+1) + (SCLL+1)] x (PRESC+1) x t_I2CCLK}.

Также есть несколько I2C_TIMINGR register configuration examples в RM0377 на странице 614.