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i2c: set hold time of SDA during transmit to an appropriate value (#273)

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* i2c: set hold time of SDA during transmit to 2 for TCS34725 color sensor

* i2c: fix issues in i2c_write_blocking_internal

* i2c: rename sda_hold_count to sda_tx_hold_count

* use assert rather than invalid_params_if for internal consistency checks

* i2c: use a more appropriate sda tx hold time at higher baudrates

* i2c: reduce 120/1e9 to the smallest possible integer numerator and denominator

* Don't use implicit 0 for field LSB

Co-authored-by: Luke Wren <wren6991@gmail.com>
This commit is contained in:
Brian Cooke 2021-04-06 11:57:25 +02:00 committed by GitHub
parent 162098678b
commit 2e777d47d3
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1 changed files with 21 additions and 0 deletions
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src/rp2_common/hardware_i2c/i2c.c
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@ -75,6 +75,24 @@ uint i2c_set_baudrate(i2c_inst_t *i2c, uint baudrate) {
invalid_params_if(I2C, hcnt < 8);
invalid_params_if(I2C, lcnt < 8);
// Per I2C-bus specification a device in standard or fast mode must
// internally provide a hold time of at least 300ns for the SDA signal to
// bridge the undefined region of the falling edge of SCL. A smaller hold
// time of 120ns is used for fast mode plus.
uint sda_tx_hold_count;
if (baudrate < 1000000) {
// sda_tx_hold_count = freq_in [cycles/s] * 300ns * (1s / 1e9ns)
// Reduce 300/1e9 to 3/1e7 to avoid numbers that don't fit in uint.
// Add 1 to avoid division truncation.
sda_tx_hold_count = ((freq_in * 3) / 10000000) + 1;
} else {
// sda_tx_hold_count = freq_in [cycles/s] * 120ns * (1s / 1e9ns)
// Reduce 120/1e9 to 3/25e6 to avoid numbers that don't fit in uint.
// Add 1 to avoid division truncation.
sda_tx_hold_count = ((freq_in * 3) / 25000000) + 1;
}
assert(sda_tx_hold_count <= lcnt - 2);
i2c->hw->enable = 0;
// Always use "fast" mode (<= 400 kHz, works fine for standard mode too)
hw_write_masked(&i2c->hw->con,
@ -84,6 +102,9 @@ uint i2c_set_baudrate(i2c_inst_t *i2c, uint baudrate) {
i2c->hw->fs_scl_hcnt = hcnt;
i2c->hw->fs_scl_lcnt = lcnt;
i2c->hw->fs_spklen = lcnt < 16 ? 1 : lcnt / 16;
hw_write_masked(&i2c->hw->sda_hold,
sda_tx_hold_count << I2C_IC_SDA_HOLD_IC_SDA_TX_HOLD_LSB,
I2C_IC_SDA_HOLD_IC_SDA_TX_HOLD_BITS);
i2c->hw->enable = 1;
return freq_in / period;