uart0 tx fifo gets broken on startup

[sapir]

I'm running code similar to the examples, and the TX FIFO gets out of sync: The right number of characters are written each loop iteration, but the current stream position is incorrect.

I think that what's happening here is that the bootloader writes some data into the FIFO, and then the reset() call in serial.rs reset the peripheral but doesn't entirely reset the FIFO. When the ESP-IDF driver initializes a uart, it doesn't reset it if it's uart0, and I think that maybe this is the reason.

I've found a few workarounds so far:

1. Commenting out the reset() call in serial.rs.
2. Resetting the TX FIFO by setting TX_FIFO_RST. This is only safe for UART0, because for UART1 it also clears UART2, and I think for UART2 it doesn't actually do anything. And also it probably messes up the output.
3. Waiting for the fifo to empty out. This messed up the previous output a bit. Possibly I didn't do it correctly, though.

[Arjan Mels]

Thanks for your troubleshooting, I'll take a look at it this weekend.

[Arjan Mels]

I cannot reproduce this (on current builds). Is there a particular exampel where you still notice this?