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Rpi port i2ctarget fixes #10933

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Rpi port i2ctarget fixes #10933

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05fae5d
raspberrypi/I2CTarget: Fixed bug where I2C starts were seen as restarts.
MarkEbrahim Jul 11, 2025
e376e24
refactor to remove common_hal_i2ctarget_i2c_target_is_stop(). Fix sep…
FoamyGuy Apr 10, 2026
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25 changes: 20 additions & 5 deletions ports/raspberrypi/common-hal/i2ctarget/I2CTarget.c
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Original file line number Diff line number Diff line change
Expand Up @@ -85,6 +85,13 @@ void common_hal_i2ctarget_i2c_target_deinit(i2ctarget_i2c_target_obj_t *self) {
}

int common_hal_i2ctarget_i2c_target_is_addressed(i2ctarget_i2c_target_obj_t *self, uint8_t *address, bool *is_read, bool *is_restart) {
// Interrupt bits must be cleared by software. Clear the STOP and
// RESTART interrupt bits after an I2C transaction finishes.
if (self->peripheral->hw->raw_intr_stat & I2C_IC_INTR_STAT_R_STOP_DET_BITS) {
self->peripheral->hw->clr_stop_det;
self->peripheral->hw->clr_restart_det;
}

if (!((self->peripheral->hw->raw_intr_stat & I2C_IC_INTR_STAT_R_RX_FULL_BITS) || (self->peripheral->hw->raw_intr_stat & I2C_IC_INTR_STAT_R_RD_REQ_BITS))) {
return 0;
}
Expand All @@ -98,12 +105,20 @@ int common_hal_i2ctarget_i2c_target_is_addressed(i2ctarget_i2c_target_obj_t *sel
}

int common_hal_i2ctarget_i2c_target_read_byte(i2ctarget_i2c_target_obj_t *self, uint8_t *data) {
if (self->peripheral->hw->status & I2C_IC_STATUS_RFNE_BITS) {
*data = (uint8_t)self->peripheral->hw->data_cmd;
return 1;
} else {
return 0;
// Wait for data to arrive or a STOP condition indicating the transfer is over.
// Without this wait, the CPU can drain the FIFO faster than bytes arrive on the
// I2C bus, causing transfers to be split into multiple partial reads.
for (int t = 0; t < 100; t++) {
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@tannewt tannewt Apr 10, 2026

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Do we want to formalize the timeout here? Maybe based on the baudrate?

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@FoamyGuy FoamyGuy Apr 11, 2026

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This is my first experience with i2ctarget side, so I'm not sure of the details. But talking it over with claude a bit and seems like the target side code does not have a reliable way to know the baudrate. The raspberrypi port implementation makes reference to setting a value here: https://github.com/FoamyGuy/circuitpython/blob/e376e2416b84d7b06f3f74843682d1d74d13efd4/ports/raspberrypi/common-hal/i2ctarget/I2CTarget.c#L52-L53 but the comment indicates it's not used.

Claude had this to say about the idea of basing it on bus speed:

the current fix is already effectively speed-independent — the loop exits early via the R_STOP_DET check as soon as the master finishes the transfer. The 1ms ceiling (100 × 10µs) is just a safety timeout, not a tuned wait. At the slowest standard I2C speed (100kHz), one byte is 9 clocks = 90µs, so 4 bytes would be ~360µs, well within the 1ms budget. The loop won't actually spin for 1ms in normal operation; it'll break out as soon as either data arrives or STOP is detected.

The values that it chose came from the atmel-samd implementation I think: https://github.com/FoamyGuy/circuitpython/blob/e376e2416b84d7b06f3f74843682d1d74d13efd4/ports/atmel-samd/common-hal/i2ctarget/I2CTarget.c#L148-L150

if (self->peripheral->hw->status & I2C_IC_STATUS_RFNE_BITS) {
*data = (uint8_t)self->peripheral->hw->data_cmd;
return 1;
}
if (self->peripheral->hw->raw_intr_stat & I2C_IC_INTR_STAT_R_STOP_DET_BITS) {
break;
}
mp_hal_delay_us(10);
}
return 0;
}

int common_hal_i2ctarget_i2c_target_write_byte(i2ctarget_i2c_target_obj_t *self, uint8_t data) {
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