esp32/machine_uart: Change sendbreak() implementation to simply pull the pin low for the break period
#17698
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@hmaerki FYI this should fix the final issue with octoprobe/testbed_micropython#36 |
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There is a testrun against this PR: https://reports.octoprobe.org/github_selfhosted_testrun_189/octoprobe_summary_report.html Please merge this PR. |
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Looks like a good improvement.
The only practical difference I can think of between doing it this way and using the UART HAL break function is that the break signal length will be exact if the peripheral hardware generates it whereas mp_hal_delay_us may delay longer than break_delay_us due to interrupts or a context switch. However, as the UART break signal is defined as a minimum pulse length this doesn't seem like a problem for correctness.
Yes, that's also my understanding, that the break is a minimum low pulse, so it's OK for it to be longer than 13 bits. |
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Currently, `UART.sendbreak()` on esp32 will reconfigure the UART to a slower baudrate and send out a null byte, to synthesise a break condition. That's not great because it changes the baudrate of the RX path as well, which could miss incoming bytes while sending the break. This commit changes the sendbreak implementation to just reconfigure the TX pin as GPIO in output mode, and hold the pin low for the required duration. Signed-off-by: Damien George <damien@micropython.org>
This is no longer needed, the esp32 port can now pass this test using just a single UART. Signed-off-by: Damien George <damien@micropython.org>
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Summary
Currently,
UART.sendbreak()on esp32 will reconfigure the UART to a slower baudrate and send out a null byte, to synthesise a break condition. That's not great because it changes the baudrate of the RX path as well, which could miss incoming bytes while sending the break.This PR changes the sendbreak implementation to just reconfigure the TX pin as GPIO in output mode, and hold the pin low for the required duration.
Testing
Existing test is updated (simplified) and works well on ESP32_GENERIC.
Also tested that RPI_PICO_W still passes this test.
Trade-offs and Alternatives
There's
uart_write_bytes_with_break()but that requires at least 1 byte to be sent before the break, so we can't use that.There's also the lower level
uart_hal_tx_break()but I'm not sure how to use that properly in conjunction with the higher level driver.