Increase double buffer size for async UART caused EACCES

RE: Increase double buffer size for async UART caused EACCES

kcl — Wed, 05 Jun 2024 02:48:51 GMT

Thanks for the suggestions! That's all the information I needed. I'll explore the options you mentioned and see what works best for my situation.

RE: Increase double buffer size for async UART caused EACCES

Vidar Berg — Tue, 04 Jun 2024 09:59:17 GMT

I think it should be possible to reliably receive the data without flow control if you utilize double buffering. You should also enable the HW counter for byte counting: https://github.com/nrfconnect/sdk-zephyr/blob/26fd55e0a750305fbd5d9db750225d7e707458ae/drivers/serial/Kconfig.nrfx_uart_instance#L45

e.g., CONFIG_UART_0_NRF_HW_ASYNC_TIMER=1 // Use TIMER1 for byte counting

The async API with DMA is your best option if you need to receive data fast with as little CPU intervention as possible.

RE: Increase double buffer size for async UART caused EACCES

kcl — Tue, 04 Jun 2024 09:51:41 GMT

Thanks for the quick reply! So, it seems like a hardware limitation with the asynchronous UARTE.

If so, are there any ways to work around this limitation? Because I'm looking for the most efficient way to handle a UART device that transmit 50KB total file size with 1024 bytes in one transaction. My though on bypass the limitation:

Increase maximum number of messages that can be queued. e.g.
K_MSGQ_DEFINE(uart_rx_msgq, sizeof(struct uart_msg_queue_item), 5, 1);
(does the mcu perform fast enough to put data from uart isr to message queue? will there any byte loss?)
Disable DMA with KConfig/command in asynchronous UART API.
if 1&2 not possible, is switching to interrupt-based approach be the only solution in this case?

Any insights or recommendations would be greatly appreciated!

RE: Increase double buffer size for async UART caused EACCES

Vidar Berg — Tue, 04 Jun 2024 09:24:11 GMT

Hello,

The UARTE DMA pointer on the nRF52832 is 8 bit wide, which limits the max. buffer size to 256 bytes.

Best regards,

Vidar