UART at higher baud rates

Manbir Jhawer

I am trying to use the UART ports on AM335x. I find everything works fine till baud rate 460.8Kbps. At 921.6 kbps, TX works fine but not RX.

I tried debugging the OMAP serial driver and I found that no interrupts were being received in the driver @921.6 kbps( IRQ function never gets triggered). I found the following thread

http://e2e.ti.com/support/arm/sitara_arm/f/791/p/298523/1102544

This thread suggests to use DMA and a different driver/SDK. Unfortunately our product uses SDK7. So it seems like a no fix for us. Can someone confirm what the thread conveys finally: Is the issue in AM335x hardware or is it a driver/linux limitation?

Also is there any possible thing I could try and see if it might work? Is it worthwhile to try and debug driver/kernel in case the issue lies only with the software side?

Thanks and Regards

Manbir Singh Jhawer

over 10 years ago

0 Yordan Kovachev over 10 years ago

TI__Guru**** 161600 points

Hi,

This is not a hw problem, the thread discuses that omap_serail driver does not enable EDMA.

Best Regards,
Yordan

0 Manbir Jhawer over 10 years ago in reply to Yordan Kovachev

Prodigy 170 points

Thanks for your reply. Appreciate it.

I have two questions:

1) Is EDMA mandatory for 921.6 Kbps?

2) Can we use another driver from SDK7.0 or do we have to move to SDK8.0 in case EDMA is mandatory?

Thanks and Regards

Manbir Singh Jhawer

0 Yordan Kovachev over 10 years ago in reply to Manbir Jhawer

TI__Guru**** 161600 points

Hi Manbir,

Sorry for the delayed response.

I think DMA is not mandatory, see Section 21.3.6.1.1 Transmit FIFO Trigger & Section 21.3.6.1.2 Receive FIFO Trigger of device TRM.
Also check your register configurations, refer to Section 21.3.8.1.2 Choosing the Appropriate Divisor Value.

Regarding your second question, you can modify your kernel to use the 8250 driver, but it may consume quite some time.

Best Regards,
Yordan

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UART at higher baud rates