topic Re: Strange problem while using UART with DMA in i.MX Processors

Strange problem while using UART with DMA

jarodnan — Tue, 12 Aug 2014 13:30:02 GMT

I've got a RSB4210(i.MX536) from Advantech and trying to use UART4 with DMA.

The bsp is from the manufacturer, and the kernel version is 2.36.35. Strange things appear if I enable the DMA of UART4.

Using printk to output some debuf message in the mxcuart_dmaread_callback() funtion of mxc_uart.c, I've got things below.

If I send 64 bytes to the RSB4210, mxcuart_dmaread_callback() is called 3 times, and the received data each time is:

1 bytes: 0x00

46 bytes: 45bytes 0x00

19 bytes: 19bytes

If I send 128 bytes to the RSB4210, mxcuart_dmaread_callback() is called 4 times, and the received data each time is:

1 bytes: 0x00

46 bytes: 45bytes 0x00

38 bytes: 38bytes

I've also merge the sdma_script_code_mx53.h, mxc_uart.c, mxc_uart.h, serial.c, serial.h from the freescale git server (http://git.freescale.com/git/cgit.cgi/imx/linux-2.6-imx.git/log/?h=imx_2.6.35_maintain). But it's still the same.

I've consult Advantech's engineers, they tell me that engineers from freescale said that it should be connected with 4 wires in DMA mode in order to avoid errors. I don't thing it has anything to do with the strange things.

Re: Strange problem while using UART with DMA

Yuri — Wed, 13 Aug 2014 04:59:37 GMT

The user should use hardware-driven hardware flow control when using
DMA data transfer. For more information, see the Linux documentation
on the serial driver in the kernel source tree.

Please take a look at section “Hardware Flow Control (RTS/CTS etc.)”
of the next document :

http://www.tldp.org/HOWTO/Text-Terminal-HOWTO-11.html

Have a great day,
Yuri

-----------------------------------------------------------------------------------------------------------------------
Note: If this post answers your question, please click the Correct Answer button. Thank you!
-----------------------------------------------------------------------------------------------------------------------

Re: Strange problem while using UART with DMA

igorpadykov — Wed, 13 Aug 2014 05:29:54 GMT

Hi Jarod

Freescale DMA driven UART driver uses flow control

(CTSTL (UARTx_UCR4) you can check below links

https://community.freescale.com/thread/304428

https://gitorious.org/u-mobo/linux-imx/commits/ed51f22bea310805bfdcc1be236cc56ff0832b3a

Best regards

chip

Re: Strange problem while using UART with DMA

jarodnan — Wed, 13 Aug 2014 10:25:22 GMT

Thanks Yuri.

Could you please explain some more for me? I've read the mx53 ref manual, but couldn't find much useful information.

How can uart without hardware flow control affect the DMA callback?

Does the RTS/CTS of mx53 works in the modern fashion or the old fashion?