Pyboard UART.sendbreak
I used the UART1 on pyboard,the baudrate is 19200bps, when used the UART.sendbreak() function, the 13 bit delay is 677uS, but actual is 520uS in oscillograph.How to solve this issue.Thanks!
esp32/machine_uart: Change `sendbreak()` implementation to simply pull the pin low for the break period
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.