QUERY · ISSUE

read() & readline() on rp2 port don't work/work as expected

openby uksconeopened 2021-02-05updated 2021-02-13

port-rp2

the UART on the rp2 port mostly works. read([num of bytes]) works mostly as expected although it seems to drop bytes occasionally and "hangs" if you try to read more bytes than currently available however read() with no number of bytes to read set and readline() just sit there indefinitely. I suspect it's to do with the fact that timeout isn't implemented

CANDIDATE · PULL REQUEST

machine.UART: Fix the double timeout with uart.read(), uart.write() and uart.readinto().

mergedby robert-hhopened 2025-08-16updated 2025-09-12

portsextmod

Summary

When uart.read(), uart.write() and uart_readinto() timed out because less data was transferred than expected, but some, the delay was uart.timeout + uart.timeout.char instead of just uart,timeout_char().

This PR changes the behavior into the expected one. It consists of 3 commits. The first changes uart.read() and uart.write(). The impact of that change is limited to the machine.UART class. The second commit changes stream.readinto() and may affect all uses of that function.
The third commit changes the ESP32's machine_uart.c to deal properly with the timeout_char argument for uart.read().

uart.readline() is unchanged.

This PR addresses issue #17611.

Testing

Tested with STM32(Pyboard V1.1 and PYBD_SF6), RP2 Pico, MIMXRT(Teensy 4.1), SAMD51, ESP32, NRF (nrf52840) and a CC3200 board using strings of varying length. Typical results:

RP2

UART(0, baudrate=38400, bits=8, parity=None, stop=1, tx=0, rx=1, txbuf=256, rxbuf=256, timeout=200, timeout_char=50, invert=None, irq=0)

uart.read() msg=""  timeout=201 ms
uart.read() msg="123"  timeout=52 ms
uart.read() msg="12345"  timeout=1 ms

uart.readline() msg=""  timeout=201 ms
uart.readline() msg="12345"  timeout=202 ms
uart.readline() msg="12345\n"  timeout=2 ms

uart.readinto(bytearray(5)) msg="" timeout=201 ms
uart.readinto(bytearray(5)) msg="123" timeout=52 ms
uart.readinto(bytearray(5)) msg="12345" timeout=1 ms

CC3200

UART(1, pins=(Pin("GP16"), Pin("GP17")))

uart.read() msg=""  timeout=36 ms
uart.read() msg="123"  timeout=38 ms (from 74 ms without the change)
uart.read() msg="12345"  timeout=5 ms

uart.readline() msg=""  timeout=35 ms
uart.readline() msg="12345"  timeout=41 ms
uart.readline() msg="12345\n"  timeout=6 ms

uart.readinto(bytearray(5)) msg="" timeout=35 ms
uart.readinto(bytearray(5)) msg="123" timeout=39 ms
uart.readinto(bytearray(5)) msg="12345" timeout=5 ms

Trade-offs and Alternatives

If the impact of the changes to a stream module seems unsafe, the second commit may be omitted, causing the behavior of uart.readinto() unchanged.