Calculate RP2040 SDA hold time #4508
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tannewt
approved these changes
Mar 29, 2021
This was referenced Mar 31, 2021
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Instead of empirically determining the I2C SDA hold time, calculate the number of clock ticks to get the 300ns required value. See https://www.nxp.com/docs/en/user-guide/UM10204.pdf#page-48, table note [3] for the origin of the 300ns value.
The hardware default is 1, but that is arbitrary, since the length depends on
ic_clk. 2 was enough to fix several I2C devices. 5 was need for PA1010D. However, the calculated value is 38 for 300ns. So the other values were quite marginal; this should be a lot safer.Tested with PA1010D, LIS3DH, BME280, BNO055, and TCS34725.
See adafruit/pico-sdk#3 for a screenshot.