Illegal use of the EPSR - uart fault

[michaelmac]

Hi, 

i have some code thats based off of the uart_async_adapter.c example code. I'm getting a `usage fault` which i've traced to uart_irq_handler. it happens when i try to send a single byte 7F over the uart. 

the strange thing is that after that fault it resets then it always works the second time. 

uart_async_adapter.c:  irq_handler

static void uart_irq_handler(const struct device *target_dev, void *context)
{
	const struct device *dev = context;
	struct uart_async_adapter_data *data = access_dev_data(dev);

	__ASSERT(target_dev == data->target,
		"IRQ handler called with a context that seems uninitialized.");
	LOG_DBG("irq_handler: Enter");
	if (uart_irq_update(target_dev) && uart_irq_is_pending(target_dev)) {
		if (data->tx.enabled && uart_irq_tx_ready(target_dev)) {
			on_tx_ready(dev, data);
		}
		if (data->tx.enabled && uart_irq_tx_complete(target_dev)) {
			on_tx_complete(dev, data);
		}
		if (data->rx.enabled && uart_irq_rx_ready(target_dev)) {
			on_rx_ready(dev, data);
		}

		/* Check errors only after all the data is received from the device */
		int rx_err = uart_err_check(target_dev);

		if (rx_err < 0) {
			rx_err = 0;
		}
		if (data->rx.enabled && rx_err) {
			on_error(dev, data, rx_err);
		}
	}
	LOG_DBG("irq_handler: Exit");
}

i get the "Notification: UART_RX_BUF_RELEASED" in the switch_rx_buffer() function, just before the crash. 

- uart_irq_handler
   - on_rx_ready(dev, data)
      - switch_rx_buffer(dev, true)
          - notify_rx_buffer_req(dev)

RTT Log:

D: tx(async_adapter, 0x2000b2dc, 1, -1)
D: tx: sending
D: irq_handler: Enter
D: on_tx_ready: Enter(async_adapter) (left: 1)
D: Pushed 1 characters
D: on_tx_ready: Exit
D: on_error: Enter(async_adapter) 12
D: Notification: UART_RX_BUF_RELEASED
E: ***** USAGE FAULT *****
E:   Illegal use of the EPSR
E: r0/a1:  0x0003b348  r1/a2:  0x20009cd4  r2/a3:  0x00030102
E: r3/a4:  0x0000e100 r12/ip:  0x200053cc r14/lr:  0x0002174f
E:  xpsr:  0x60000012
E: Faulting instruction address (r15/pc): 0x0000e100
E: >>> ZEPHYR FATAL ERROR 35: Unknown error on CPU 0
E: Fault during interrupt handling

I modified the log_dbg message in the on_error() function to include the rx_err code, which is `12`.  i think this means UART_ERROR_FRAMING & UART_BREAK

not sure if its because the other end of the uart (another mcu) is being configured to enable its uart, before sending the data, and so causing some noise.  is there a way to basically clear any pending interrupts and rx buffer in the nrf device? 

sorry hope that makes some sense, i can provide more details if needed. 

many thanks,

michael.

[Einar Thorsrud]

Hi,

The driver handles clearing of interrupts etc, and there is no high level API for that nor should it be neeeded. It would be good to understand a bit more about this issue first.

You write that you try to send a byte over UART, do then mean to the nRF, so that it is receiving? I ask just to confirm, as a framing error or break error would be related to reception/input and that match the other informaiton here. Also, can you elaborate more on what you do and the configuration? Are you using flow control? If not, does flow control help?

PS: Sometimes it can be a problem with UART fi you have a inaccurate HF clock, so it could be worth enabling the HFXO and seeing if that makes a difference (as mentionned here).