AM335x UART fails into frame error, break condition in FIFO interrupt mode

Tim Tang

We've faced issue with UART configured in FIFO interrupt mode with HW flow control. All of reference code (Linux driver were checked as well) uses DMA. It's not possible to use DMA now as all of channels are in use.

In FIFO interrupt mode UART logic triggers one of following interrupts:

frame error

break condition

parity error

Issue occurs under following conditions:

UART configured in FIFO interrupt mode

size of receiving packet is more then RX_FIFO threshold level. i.e. if FIFO threshold configured to 4 and packet for example 6 bytes one of described above interrupts will come. When 4 bytes received UART issues UART_INTID_RX_THRES_REACH IRQ. Depending on what kind of data is byte #5 either one or combination of UART_INTID_RX_LINE_STAT_ERROR comes.

In attachment architecture diagram with red circles marks where issue might occur

over 10 years ago

0 Biser Gatchev-XID over 10 years ago

TI__Guru**** 393215 points

Hi Tim,

What baud rate are you using? Have you tried to raise the interrupt priority? Are you working under Linux or other software?

0 Tim Tang over 10 years ago in reply to Biser Gatchev-XID

Prodigy 30 points

Hi Biser,

We are using 3Mbps. We are not using Linux but another software platform.

Regarding interrupt priority, do you have any suggestions or guidelines? We will try your suggestion.

Thanks,

0 Biser Gatchev-XID over 10 years ago in reply to Tim Tang

TI__Guru**** 393215 points

Hi Tim,

For setting interrupt priority check section 6 of the AM335X Technical Reference Manual, Rev. I. Other than that 3Mbps is close to the theoretical limit that this UART can support. Have you checked the RX signal for distortions with an oscilloscope? I don't know if this is possible in your environment, but can you try to format the RX signal with two stop bits on the transmit side only? This will help by introducing one bit more inter-character delay. If the signal is distorted you can try adding a serial resistor (~ 22Ohm) on the RX line.

0 Artur Troian1 over 10 years ago in reply to Biser Gatchev-XID

Prodigy 20 points

Hi Biser,

This issue occurs on any speed we're trying to use (even 115200) in this specific mode (FIFO interrupt). RX/TX and HW flow control signals are fine (i.e. no distortions etc). Unfortunately our environment doesn't allow to use two stop bits.

0 Biser Gatchev-XID over 10 years ago in reply to Artur Troian1

TI__Guru**** 393215 points

Hi Artur,

We can eliminate hardware problems then. I can't help much, since you are using custom software. Please check carefully that you have followed section 19.4.1.2.1 from the AM335X Technical Reference Manual, Rev. I. Also read the description in section 19.5.1.20 - it may be related to your problem. There is also an Advisory 1.0.35 in the latest AM335X Errata Rev. F, though I doubt that this is the case.

0 Artur Troian1 over 10 years ago in reply to Biser Gatchev-XID

Prodigy 20 points

Yes, followed instructions in TRM that you just mentioned.

0 Daniel Haslimann over 10 years ago in reply to Artur Troian1

Intellectual 810 points

Artur,

have you found a solution for the problem in the meantime?
We have similiar issues here.

Regards,
Daniel

Processors

Processors forum

AM335x UART fails into frame error, break condition in FIFO interrupt mode