i2c: set hold time of SDA during transmit to an appropriate value (#273)
* 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>
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@ -75,6 +75,24 @@ uint i2c_set_baudrate(i2c_inst_t *i2c, uint baudrate) {
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invalid_params_if(I2C, hcnt < 8);
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invalid_params_if(I2C, hcnt < 8);
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invalid_params_if(I2C, lcnt < 8);
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invalid_params_if(I2C, lcnt < 8);
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// Per I2C-bus specification a device in standard or fast mode must
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// internally provide a hold time of at least 300ns for the SDA signal to
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// bridge the undefined region of the falling edge of SCL. A smaller hold
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// time of 120ns is used for fast mode plus.
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uint sda_tx_hold_count;
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if (baudrate < 1000000) {
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// sda_tx_hold_count = freq_in [cycles/s] * 300ns * (1s / 1e9ns)
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// Reduce 300/1e9 to 3/1e7 to avoid numbers that don't fit in uint.
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// Add 1 to avoid division truncation.
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sda_tx_hold_count = ((freq_in * 3) / 10000000) + 1;
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} else {
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// sda_tx_hold_count = freq_in [cycles/s] * 120ns * (1s / 1e9ns)
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// Reduce 120/1e9 to 3/25e6 to avoid numbers that don't fit in uint.
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// Add 1 to avoid division truncation.
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sda_tx_hold_count = ((freq_in * 3) / 25000000) + 1;
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}
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assert(sda_tx_hold_count <= lcnt - 2);
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i2c->hw->enable = 0;
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i2c->hw->enable = 0;
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// Always use "fast" mode (<= 400 kHz, works fine for standard mode too)
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// Always use "fast" mode (<= 400 kHz, works fine for standard mode too)
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hw_write_masked(&i2c->hw->con,
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hw_write_masked(&i2c->hw->con,
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@ -84,6 +102,9 @@ uint i2c_set_baudrate(i2c_inst_t *i2c, uint baudrate) {
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i2c->hw->fs_scl_hcnt = hcnt;
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i2c->hw->fs_scl_hcnt = hcnt;
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i2c->hw->fs_scl_lcnt = lcnt;
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i2c->hw->fs_scl_lcnt = lcnt;
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i2c->hw->fs_spklen = lcnt < 16 ? 1 : lcnt / 16;
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i2c->hw->fs_spklen = lcnt < 16 ? 1 : lcnt / 16;
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hw_write_masked(&i2c->hw->sda_hold,
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sda_tx_hold_count << I2C_IC_SDA_HOLD_IC_SDA_TX_HOLD_LSB,
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I2C_IC_SDA_HOLD_IC_SDA_TX_HOLD_BITS);
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i2c->hw->enable = 1;
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i2c->hw->enable = 1;
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return freq_in / period;
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return freq_in / period;
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