serial: uart_native_pty: ASYNC API support #87874

JordanYates · 2025-03-30T23:38:11Z

Add support for the ASYNC API to the native PTY uart driver.
Asynchronous transmission is performed from the system workqueue.
Asynchronous reception is performed from a dedicated thread.

I would love to add testing for testing this to tests/drivers/uart/uart_async_api, but it depends on loopback support.
As far as I can tell the basic polling API is not tested either due to the lack of this support. Does anyone have ideas for enabling this in CI?

aescolar

Unfortunately this is not an approach we can use, due to several issues, of which the main are:

A signal is delivered fully asynchronously to the native_simulator execution
The signal handler will by default be run by any native simulator thread
That means between other things that the signal handler will be run, for ex., while the CPU is sleeping corrupting the kernel state; for AMP targets, from any other CPU thread, causing mayhem in both CPUs kernels state, and other messy situations.

In general in native_sim we do not have really asynchronous behaviors. What we do is that we have a deterministic synchronous one that pretends to inject an asynchronous like event at a very deterministic time (see for example the TTY UART interrupt driven mechanism).

drivers/serial/uart_native_pty.c

drivers/serial/uart_native_pty_bottom.c

drivers/serial/uart_native_pty.c

JordanYates · 2025-04-16T08:27:38Z

Unfortunately this is not an approach we can use, due to several issues, of which the main are:
1. A signal is delivered fully asynchronously to the native_simulator execution

2. The signal handler will by default be run by _any_ native simulator thread
   That means between other things that the signal handler will be run, for ex., while the CPU is sleeping corrupting the kernel state; for AMP targets, from any other CPU thread, causing mayhem in both CPUs kernels state, and other messy situations.
In general in native_sim we do not have really asynchronous behaviors. What we do is that we have a deterministic synchronous one that pretends to inject an asynchronous like event at a very deterministic time (see for example the TTY UART interrupt driven mechanism).

Thanks for the feedback, I have reworked the PR in line with the TTY driver.
I also added an ASYNC API sample that can be used with the new driver.

aescolar

Thanks @JordanYates
What I see now is much more minor.
And probably people who is more familiar with the UART API is better than me to provide good input for what remains (CC @dcpleung @nordic-krch )

drivers/serial/uart_native_pty.c

aescolar · 2025-04-22T14:32:31Z

drivers/serial/uart_native_pty.c

+
+static int np_uart_tx(const struct device *dev, const uint8_t *buf, size_t len, int32_t timeout)
+{
+	struct native_pty_status *data = dev->data;


should this check if the callback is set and return -ENOTSUP otherwise?
(Same for rx and np_uart_tx_abort)

That isn't done in the other drivers that I have inspected

Ok, I based my comment on the API header comments. I leave it up to the driver class owner @dcpleung to decide if anything needs doing

samples/drivers/uart/async_api/src/main.c

Add a length parameter to the poll in read function so that data can be read in larger chunks. Signed-off-by: Jordan Yates <[email protected]>

JordanYates · 2025-04-22T23:26:36Z

@aescolar thanks for the feedback, halfway through the implementation I switched from a persistent thread to one that only runs while RX is enabled and missed some things.

Add support for transmitting using the asynchronous API. The asynchronous portion is simulated through the system workqueue. Signed-off-by: Jordan Yates <[email protected]>

Add support for transmitting using the asynchronous API. The asynchronous portion is simulated through a dedicated polling thread. Signed-off-by: Jordan Yates <[email protected]>

Add a sample that utilises the ASYNC API to queue packets in bursts. Signed-off-by: Jordan Yates <[email protected]>

nordic-krch · 2025-04-23T05:25:51Z

drivers/serial/uart_native_pty.c

+	data->async.tx_buf = NULL;
+
+	if (data->async.user_callback) {
+		data->async.user_callback(data->async.dev, &evt, data->async.user_data);


Maybe not critical for native but normally user callback should not be called with interrupts locked.

The goal here was to prevent the system workqueue item being preempted by some other thread while this function was running, since in a "normal" driver this logic would be running from an interrupt context. Happy to use a different solution if you have one.

nordic-krch · 2025-04-23T05:29:59Z

drivers/serial/uart_native_pty.c

+	}
+
+	/* Generate TX_DONE event with number of bytes transmitted */
+	evt.type = UART_TX_DONE;


UART_TX_ABORTED

The UART documentation contradicts itself on which event should be generated:

zephyr/include/zephyr/drivers/uart.h

Lines 195 to 196 in 6463c68

* Transmitting can be aborted using @ref uart_tx_abort, after calling that

* function #UART_TX_ABORTED event will be generated.

zephyr/include/zephyr/drivers/uart.h

Line 800 in 6463c68

* #UART_TX_DONE event will be generated with amount of data sent.

nordic-krch · 2025-04-23T05:36:39Z

drivers/serial/uart_native_pty.c

+	ARG_UNUSED(arg2);
+	ARG_UNUSED(arg3);
+
+	while (data->async.rx_len) {


the expected receiver behavior is that RX_RDY is reported when buffer is filled or when timeout occurs (and no new data arrives). When buffer is filled and new buffer is not provided then RX_BUF_RELEASED followed by RX_DISABLED events will be generated.

nordic-krch · 2025-04-23T05:37:58Z

samples/drivers/uart/async_api/src/main.c

+	case UART_RX_BUF_REQUEST:
+		/* Return the next buffer index */
+		LOG_DBG("Providing buffer index %d", async_rx_buffer_idx);
+		rc = uart_rx_buf_rsp(dev, async_rx_buffer[async_rx_buffer_idx],


it will assert with current implementation

It won't, because the native driver never issues UART_RX_BUF_REQUEST, since it has no need for multiple buffers.

There could be an argument to be made to simulate the ping-pong buffers though to more closely behave like a real hardware device.

It won't, because the native driver never issues UART_RX_BUF_REQUEST, since it has no need for multiple buffers.

But this is a generic sample for all UART drivers supporting the ASYNC API, or?

My comment was in reference to what I thought @nordic-krch was referring to, which was that uart_rx_buf_rsp would return -ENOTSUP for the native driver, and thus trigger the assertion. If that is not the case I would need clarification on the "will assert" comment.

aescolar

+2 for the native/host integration side
+1 for driver API/behaviour side

github-actions bot added area: native port Host native arch port (native_sim) area: UART Universal Asynchronous Receiver-Transmitter labels Mar 30, 2025

github-actions bot requested review from aescolar and dcpleung March 30, 2025 23:38

github-actions bot assigned aescolar Mar 30, 2025

JordanYates force-pushed the 250330_pty_async branch 2 times, most recently from d408832 to 95f5aab Compare March 31, 2025 00:14

aescolar requested changes Mar 31, 2025

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dramaticlama reviewed Apr 1, 2025

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JordanYates force-pushed the 250330_pty_async branch from 95f5aab to 2dda4d3 Compare April 16, 2025 08:25

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serial: uart_native_pty_bottom: length parameter

6e29a33

Add a length parameter to the poll in read function so that data can be read in larger chunks. Signed-off-by: Jordan Yates <[email protected]>

JordanYates force-pushed the 250330_pty_async branch 2 times, most recently from 3bbfee8 to 3f3d17f Compare April 22, 2025 23:24

JordanYates force-pushed the 250330_pty_async branch from 3f3d17f to 0614be0 Compare April 22, 2025 23:39

JordanYates added 3 commits April 23, 2025 09:44

serial: uart_native_pty: ASYNC TX support

49baca0

Add support for transmitting using the asynchronous API. The asynchronous portion is simulated through the system workqueue. Signed-off-by: Jordan Yates <[email protected]>

serial: uart_native_pty: ASYNC RX support

38ae475

Add support for transmitting using the asynchronous API. The asynchronous portion is simulated through a dedicated polling thread. Signed-off-by: Jordan Yates <[email protected]>

samples: uart: async_api: added

e06e72e

Add a sample that utilises the ASYNC API to queue packets in bursts. Signed-off-by: Jordan Yates <[email protected]>

JordanYates force-pushed the 250330_pty_async branch from 0614be0 to e06e72e Compare April 22, 2025 23:45

nordic-krch reviewed Apr 23, 2025

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aescolar approved these changes Apr 25, 2025

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aescolar assigned dcpleung Apr 25, 2025

aescolar removed their assignment Apr 25, 2025

dcpleung approved these changes Apr 25, 2025

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kartben merged commit bb0f192 into zephyrproject-rtos:main Apr 25, 2025
24 checks passed

JordanYates deleted the 250330_pty_async branch April 25, 2025 22:18

DerekSnell mentioned this pull request Apr 26, 2025

samples/drivers/uart/async_api fails to build on many NXP platforms with LPUART #89142

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serial: uart_native_pty: ASYNC API support #87874

serial: uart_native_pty: ASYNC API support #87874

JordanYates commented Mar 30, 2025 •

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	* Transmitting can be aborted using @ref uart_tx_abort, after calling that
	* function #UART_TX_ABORTED event will be generated.

serial: uart_native_pty: ASYNC API support #87874

serial: uart_native_pty: ASYNC API support #87874

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