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samd: diagnose out of range I2C frequency

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The frequency divisor is limited to 255, which gives 48MHz/2/255 ~= 94.1kHz as
the lowest speed.

Without this change, values below this cut-off gave higher frequencies instead,
which didn't appear to have any relation to the frequency value requested.

Closes: #4883
This commit is contained in:
Jeff Epler 2021-08-20 14:05:40 -05:00
parent cabe96e188
commit 26d33658ea
1 changed files with 7 additions and 0 deletions
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7
ports/atmel-samd/common-hal/busio/I2C.c
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@ -119,6 +119,13 @@ void common_hal_busio_i2c_construct(busio_i2c_obj_t *self,
// clkrate is always 0. baud_rate is in kHz.
// Frequency must be set before the I2C device is enabled.
// The maximum frequency divisor gives a clock rate of around 48MHz/2/255
// but set_baudrate does not diagnose this problem. (This is not the
// exact cutoff, but no frequency well under 100kHz is available)
if (frequency < 95000) {
mp_raise_ValueError(translate("Unsupported baudrate"));
}
if (i2c_m_sync_set_baudrate(&self->i2c_desc, 0, frequency / 1000) != ERR_NONE) {
reset_pin_number(sda->number);
reset_pin_number(scl->number);