Each SoC family has its own clocks and timings/timeouts. For I2C, the
default source clock is either APB (ESP32, ESP32-S2) or XTAL (ESP32-S3,
ESP32-C3) as shown in the datasheets. Since
machine_i2c.c/machine_hw_i2c_init() uses the default clk_flags (0), the
alternate low-power clock source is never selected in ESP-IDF
i2c.c/i2c_param_config(). There is not an API in i2c.c to get the source
clock frequency, so a compile-time value is used based on SoC family.
Also, the maximum timeout is different across the SoC families, so use the
I2C_LL_MAX_TIMEOUT constant to eliminate the warning from
i2c_set_timeout().
With these changes, the following results were obtained. The I2C SCL
frequencies were measured with a Saleae logic analyzer.
ESP32 (TTGO T Dislay)
I2C(0, scl=22, sda=21, freq=101781) Measured: 100KHz
I2C(0, scl=22, sda=21, freq=430107) Measured: 400KHz
I2C(0, scl=22, sda=21, freq=1212121) Measured: 941KHz
ESP32-S3 (TTGO T-QT)
I2C(0, scl=34, sda=33, freq=111111) Measured: 107KHz
I2C(0, scl=34, sda=33, freq=444444) Measured: 400KHz
I2C(0, scl=34, sda=33, freq=1111111) Measured: 842KHz
ESP32-C3 (XIAO ESP32C3)
I2C(0, scl=7, sda=6, freq=107816) Measured: 103KHz
I2C(0, scl=7, sda=6, freq=444444) Measured: 380KHz
I2C(0, scl=7, sda=6, freq=1176470) Measured: 800KHz
(ESP32-S2 board was not available for testing.)
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