And probably this one: #1314

The above "Port UART reset fix from ESP-IDF #1408 [chemicstry]" fixed my ESP32 issue with corrupt Serial-ports after an “ESP.restart()” – very many thanks!

[PS. FYI: I was basically just using “while (Serial2.available()) Serial.write(Serial2.read()); while (Serial.available()) Serial2.write(Serial.read());” to transfer data to & from a GSM-module.]

@chemicstry will you please make the adjustment that I requested so I can merge this? Thanks :)

@me-no-dev I do not see any comment where you requested adjustments. Could you repeat?

Not seeing this?

I believe there is some missing parts which is needed in case of arduino.

1. uart queue must be emptied after reading all of the characters.
   Without it, available functions returns non-zero value after flush.
2. Flush needs to detach ISR, then attachs it afterwards.
   Otherwise while reading from the hardware buffer, ISR can read data to queue, since the process is not atomic.

I think disable and enable functions can do that. Something similar should suffice:

@me-no-dev

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@me-no-dev At first I tried using uart->dev->fifo.rw_byte but compiler optimises dummy reading and it does not work unless I write some ugly assembler stuff. READ_PERI_REG macro is deeply integrated into IDF and I was unable to trace back how it actually works. Is there an example in arduino code on how to dummy read register or maybe you have a suggestion on how to do it?

Regarding the interrupts @sysizlayan. When uartFlush() is called during UART initialization, ISR is not enabled yet and it should not spit any data out. However, HardwareSerial::flush(), which uses uartFlush() has different behaviour and I think different function should be used. flush is intended to wait for data transfer to complete instead of reseting. Maybe uartFlush() should really be uartReset().

@negativekelvin holly cow! I was unaware of this... thanks for pointing out!

@chemicstry maybe use some dummy holder for the bytes?

uint8_t dummy;
while(uart->dev->status.rxfifo_cnt != 0 || (uart->dev->mem_rx_status.wr_addr != uart->dev->mem_rx_status.rd_addr)) {
  dummy = uart->dev->fifo.rw_byte;
}

As @chemicstry said, Serial.flush() behaves differently than expected of the Arduino API, clearing not only the TX buffer but also the RX buffer. Are there any plans to change this?