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Calculate proper I2C SDA hold time #3

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Merged
dhalbert merged 1 commit into from
Mar 29, 2021
Merged

Calculate proper I2C SDA hold time #3

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11 changes: 6 additions & 5 deletions src/rp2_common/hardware_i2c/i2c.c
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Original file line number Diff line number Diff line change
Expand Up @@ -85,13 +85,14 @@ uint i2c_set_baudrate(i2c_inst_t *i2c, uint baudrate) {
i2c->hw->fs_scl_lcnt = lcnt;
i2c->hw->fs_spklen = lcnt < 16 ? 1 : lcnt / 16;

// Set hold time of SDA during transmit to 2. Several I2C devices need
// this fix to work well or at all, including the
// TCS34725 color sensor, and the SSD1306 and SH1107 OLED drivers.
// There is no discernable slowdown in timing traces.
// The SDA hold time should be at least 300 ns, per the I2C standard.
// sda_hold_count [cycles] = freq_in [cycles/s]) * 300ns * (1s / 1e9ns)
// Reduce 300/1e9 to 3/1e7 to avoid really big numbers.
// Add 1 to avoid division truncation.
uint sda_hold_count = ((freq_in * 3) / 10000000) + 1;
i2c->hw->sda_hold =
I2C_IC_SDA_HOLD_IC_SDA_RX_HOLD_RESET << I2C_IC_SDA_HOLD_IC_SDA_RX_HOLD_LSB |
2 << I2C_IC_SDA_HOLD_IC_SDA_TX_HOLD_LSB;
sda_hold_count << I2C_IC_SDA_HOLD_IC_SDA_TX_HOLD_LSB;
i2c->hw->enable = 1;
return freq_in / period;
}
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