UARTSerial writes even if tx is disabled

[ghseb]

UARTSerial::_tx_enabled and UARTSerial::_rx_enabled shadow SerialBase::_tx_enabled and SerialBase::_rx_enabled.

mbed-os/drivers/UARTSerial.h

Lines 299 to 300 in 0be7685

	bool _tx_enabled;
	bool _rx_enabled;

mbed-os/drivers/SerialBase.h

Lines 354 to 355 in 0be7685

	bool _rx_enabled = true;
	bool _tx_enabled = true;

This essentially leads to data being written out even if the serial is disabled, because UARTSerial::_tx_enabled is always true. In my opinion this is not the desired behaviour.

mbed-os/drivers/source/UARTSerial.cpp

Lines 199 to 206 in 0be7685

	core_util_critical_section_enter();
	if (_tx_enabled && !_tx_irq_enabled) {
	UARTSerial::tx_irq(); // only write to hardware in one place
	if (!_txbuf.empty()) {
	enable_tx_irq();
	}
	}
	core_util_critical_section_exit();

Summary of changes

Remove shadowing variables.

Impact of changes

Migration actions required

Documentation

---

Pull request type

[x] Patch update (Bug fix / Target update / Docs update / Test update / Refactor)
[] Feature update (New feature / Functionality change / New API)
[] Major update (Breaking change E.g. Return code change / API behaviour change)

---

Test results

[] No Tests required for this change (E.g docs only update)
[x] Covered by existing mbed-os tests (Greentea or Unittest)
[] Tests / results supplied as part of this PR

---

Reviewers

---

[ciarmcom]

@ghseb, thank you for your changes.
@ARMmbed/mbed-os-maintainers please review.

[0xc0170]

I can't think of why it would shadow it like this.

[0xc0170]

CI restarted

[ghseb]

@0xc0170 I think im not able to determine why the check failed.

[0xc0170]

True, I'll restart now

[mbed-ci]

Test run: SUCCESS

Summary: 10 of 10 test jobs passed
Build number : 1
Build artifacts

[ghseb]

There probably is a flaw in the UARTSerial/SerialBase implementation hat can cause infinite congestion with this change in place. I'm going to investigate the issue and come back when I have something. I'd propose to not yet merge this one.

[ghseb]

The following snippet forces the issue:

    mbed::UARTSerial serial(USBTX, USBRX, MBED_CONF_PLATFORM_STDIO_BAUD_RATE);
    serial.set_blocking(false);
    serial.enable_input(false);
    serial.enable_output(false);

    // Must write at least MBED_CONF_DRIVERS_UART_SERIAL_TXBUF_SIZE bytes to reproduce
    // the issue.
    auto const *fill_string { "Fill UARTSerial buffer" };
    for (int i=0; i<MBED_CONF_DRIVERS_UART_SERIAL_TXBUF_SIZE; ++i) {
        serial.write(fill_string, strlen(fill_string));
    }

    serial.enable_input(true);
    serial.enable_output(true);
    serial.set_blocking(true);

    /**
     * Situation:
     * - tx-buffer of UARTSerial is full
     * - tx-irq is not enabled (`UARTSerial::enable_output(true)` does not enable the tx-irq)
     * - UARTSerial is set blocking
     *
     * If in this situation another write is issued, UARTSerial blocks infinitely because
     * the tx-irq that is supposed to empty the tx-buffer is not active.
     */
    auto const *doom_string { "DOOOOM" };
    serial.write(doom_string, strlen(doom_string));

    // Will never be reached
    auto foo { 2 };

I'd add a fix in this PR.

Pull request has been modified.

[kjbracey]

Looks basically reasonable to me - just bikeshedding. Going to need this on master too I guess? Is there already another PR for that?

[kjbracey]

Looks good to me. But we need a version for BufferedSerial on master too. Can't be making fixes only on the 5.15 branch.

[ghseb]

Well I never used mbed-os-6 or BufferedSerial until now. I could create a PR but I think im not able to test it in the near future.

[0xc0170]

Thjank you ! I'll retart CI

[mbed-ci]

Test run: FAILED

Summary: 1 of 10 test jobs failed
Build number : 2
Build artifacts

Failed test jobs:

• jenkins-ci/mbed-os-ci_example-test-lts

[mbed-ci]

Test run: FAILED

Summary: 1 of 10 test jobs failed
Build number : 3
Build artifacts

Failed test jobs:

• jenkins-ci/mbed-os-ci_example-test-lts

[ciarmcom]

This pull request has automatically been marked as stale because it has had no recent activity. @ghseb, please carry out any necessary work to get the changes merged. Thank you for your contributions.

[ghseb]

I think this error is not related.

[0xc0170]

I'll restart CI

[0xc0170]

we got an issue it seems with lts example,, I'll investigate today.

[0xc0170]

CI restarted (deprecated example was removed)

[mbed-ci]

Test run: SUCCESS

Summary: 10 of 10 test jobs passed
Build number : 4
Build artifacts