STM32 - USART - Non Blocking Read

[Ralim]

Hello,

I've noticed that all of the USART drivers implement the embedded hal for read() which specifies that they should block if there is no pending data. For my current application I would be able to reduce logic complexity if I could poll these or only read the pending data rather than having to use separate tasks that may block on a read.

Would there be any room in the future to have some form of API to provide either a non-blocking read (just read out anything pending) or some way to check there is pending data (so can avoid a read if no data)?

In this context by blocking I mean both the traditional sense as well as a Future that stays pending until there is data available).

[Dirbaio]

BufferedUart / RingbufferedUart do exactly that, .read() immediately returns the available data without having to wait for the buffer to fill up.

[Ralim]

Hia,

What I'm referring to is these lines ringbuffered.read

buffered.read

Where if there is no data pending, it blocks for some data.

I'm looking for a way to read only the pending without blocking for following data.

[phycrax]

I think it would be possible to use poll_once for your use case.

[Dillonmcewan]

I ran into a similar issue. We're transitioning from a sync implementation using the stm32-rs crates. We were able to hack a solution using block_on (I'm guessing poll_once would probably also work), so we didn't block execution while waiting for data. It seems like the correct way to do this with the embedded_io traits would be to have the various USART structs implement ReadReady. That way you could do something like:

let ready = rx.read_ready()?;
if ready {
    rx.read(&mut rx_buf)?;
}

[kpfleming]

ReadReady is now available, although it's not an async function so you have to poll it.