Receiving junk data while running rs485 send and receive application on imx6dl

[sujay1]

I'm using an imx6dl board with Android BSP. 

I'm running a custom application on the board where I configure my Linux PC as a sender and the board a receiver.

The PC transmits * Bytes of data at 38400 Baudrate and the board is supposed to capture this data print the value received and send it back to the PC.

The PC then echos the data received from the board. We expect to see the same bytes being received from the board,

however we get a large burst of noise at times on the sender side (PC).

Here is the log:

Sender:

> B7 02 00 00 00 00 00 00
< B7 02 00 00 00 00 00 00

> B8 02 00 00 00 00 00 00
< B8 02 00 00 00 00 00 00

> B9 02 00 00 00 00 00 00
< B9 02 00 00 00 00 00 00

> BA 02 00 00 00 00 00 00

< BA 02 BA 02 00 00 00 00 00 00 00 00 00 00 00 00 BC 00 00 00 00 00 00 00 BD 00 00 00 00

> BB 02 00 00 00 00 00 00
< 00 00 00 BE 00 00 00 00 00 00 00 BF 00 00 00 00 00 00 00 C0 00 00 00 00 00 00 00 C1 00 00 00 00 00 00 00 C2 00 00 00 00 00 00 00 C3 00 00 00 00 00 00 00 C4 00 00 00 00 00 00 00 C5 00 00 00 00 00 00 00 C6 00 00 00 00 00 00 00 C7 00 00 00 00 00 00 00 C8 00 00 00 00 00 00 00 C9 00 00 00 00 00 00 00 CA 00 00 00 00 00 00 00 CB 00 00 FF 40 80 80 00 00 CD 00 00 00 00 00 00 00 CE 00 00 00 00 00 00 00 CF 00 00 00 00 00 00 00 D0 00 00 00 00 00 00 00 D1 00 00 00 00 00 00 00 D2 00 00 00 00 00 00 00 D3 00 00 00 00 00 00 00 D4 00 00 00 00 00 00 00 D5 00 00 00 00 00 00 00 D6 00 00 00 00 00 00 00 D7 00 00 00 00 00 00 00 D8 00 00 00 00 00 00 00 D9 00 00 00 00 00 00 00 DA 00 00 00 00 00 00 00 DB 00 00

> BC 02 00 00 00 00 00 00
< 00 00 00 00 00 DC 00 00 00 00 00 00 00 DD 00 00 00 00 00 00 00 DE 00 00 00 00 00 00 00 DF 00 00 00 00 00 00 00 E0 00 00 00 00 00 00 00 E1 00 00 00 00 00 00 00 E2 00 00 00 00 00 00 00 E3 00 00 00 00 00 FC 10 A0 1E 20 20 40 40 80 80 00 E6 00 00 00 00 00 00 00 E7 00 00 00 00 00 00 00 E8 00 00 00 00 00 00 00 E9 00 00 00 00 00 00 00 EA 00 00 00 00 00 00 00 EB 00 00 00 00 00 00 00 EC

> BD 02 00 00 00 00 00 00
< 00 00 00 00 00 00 00 ED 00 00 00 00 00 00 00 EE 00 00 00 00 00 00 00 EF 00 00 00 00 00 00 00 F0 00 00 00 00 00 00 00 F1 00 00 00 00 00 00 00 F2 00 00 00 00 00 00 00 F3 00 00 00 00 00 00 E0 AA 00 00 00 00 00 00 00 F6 00 00 00 00 00 00 00 F7 00 00 00 00 00 00 00 F8 00 00 00 00 00 00 00 F9 00 00 00 00 00 00 00 FA 00 00 00 00 00 00 00

> BE 02 00 00 00 00 00 00
< FB 00 00 00 00 00 00 00 FC 00 00 00 00 00 00 00 FD 00 00 00 00 00 00 00 FE 00 00 00 00 00 00 00 FF 00 00 00 00 00 00 00 00 01 00 00 00 00 00 00 01 01 00 00 00 00 00 00 02 01 00 00 00 00 00 00 03 01 00 00 00 00 00 00 04 01 00 00 00 00 00 00 05 01 00 00 00 00 00 00 06 01 00 00 00 00 00 00 07 01 00 00 00 00 00 00 08 01 00 00 00 00 00 00 09 01 00 00 00 00 00 FC D0 A1 20 40 40 80 80 00 00 0C 01 00 00 00 00 00 00 0D 01 00 00 00 00 00 00 0E 01 00 00 00 00 00 00 0F 01 00 00 00 00 00 00 10 01 00 00 00 00 00 00 11 01 00 00 00 00 00 00 12 01 00 00

> BF 02 00 00 00 00 00 00
< 00 00 00 00 13 01 00 00 00 00 00 00 14 01 00 00 00 00 00 00 15 01 00 00 00 00 00 00 16 01 00 00 00 00 00 00 17 01 00 00 00 00 00 00 18 01 00 00 00 00 00 00 19 01 00 00 00 00 00 00 1A 01 00 00 00 00 00 00 1B 01 00 00 00 00 00 00 1C 01 00 00 00 00 00 00 1D 01 00 00 00 00 00 00 1E 01 00 00 00 00 00 00 1F 01 00 00 00 FE 20 20 40 48 40 80 80 00 00 00 00 22 01 00 00 00 00 00 00 23 01 00 00 00 00 00 00 24 01 00 00 00 00 00 00 25 01 00 00 00 00 00 00 26 01 00 00 00 00 00 00 27 01 00 00 00 00 00 00 28 01 00 00 00 00 00 00 29 01 00 00 00 00 00 00 2A 01 00 00 00 00 00 00 2B 01 00 00 00 00 00 00 2C 01 00 00 00 00 00 00 2D 01 00 00 00 00 00 00 2E 01 00 00 00 00 00 00 2F 01 00 00 00 00

> C0 02 00 00 00 00 00 00
< 00 00 30 01 00 00 00 00 00 00 31 01 00 00 00 00 00 00 32 01 00 00 00 FC 10 20 20 4D 40 80 80 00 00 00 00 35 01 00 00 00 00 00 00 36 01 00 00 00 00 00 00 37 01 00 00 00 00 00 00 38 01 00 00 00 00 00 00 39 01 00 00 00 00 00 00 3A 01 00 00 00 00 00 00 3B 01 00 00 00 00 00 00 3C 01 00 00 00 00 00 00 3D 01 00 00 00 00 00 00 3E 01 00 00 00 00 00 00 3F 01 00 00 00 00 00 00 40 01 00 00 00 00 00 00 41 01 00 00 00 00 00 00 42 01 00 00 00 00 00 00

> C1 02 00 00 00 00 00 00
< 43 01 00 00 00 00 00 00 44 01 00 E0 02 02 04 04 C8 2A 10 10 20 20 40 40 80 54 20 20 40 40 80 80 00 48 01 00 00 00 00 00 00 49 01 00 00 00 00 00 00 4A 01 00 00 00 00 00 00 4B 01 00 00 00 00 00 00 4C 01 00 00 00 00 00 00 4D 01 00 00 00 00 00 00 4E 01 00 00 00 00 00 00 4F 01 00 00 00 00 00 00 50 01 00 00 00 00 00 00 51 01 00 00 00 00 00 00 52 01 00 00 00 00 00 00 53 01 00 00 00 00 00 00 54 01 00 00 00 00

> C2 02 00 00 00 00 00 00
< 00 00 55 01 00 00 00 00 00 00 56 01 00 00 00 00 00 00 57 01 00 00 00 00 00 00 58 01 00 00 FE 20 40 40 80 AD 01 00 00 00 00 00 00 5B 01 00 00 00 00 00 00 5C 01 00 00 00 00 00 00 5D 01 00 00 00 00 00 00 5E 01 00 00 00 00 00 00 5F 01 00 00 00 00 00 00 60 01 00 00 00 00 00 00 61 01 00 00 00 00 00 00 62 01 00 00 00 00 00 00 63 01 00 00 00 00 00 00 64 01 00 00 00 00 00 00 65 01 00 00 00 00 00 00 66 01 00 00 00 00 00 00 67 01 00 00 00 00 00 00 68 01 00 00 00 00 00

> C3 02 00 00 00 00 00 00
< 00 69 01 00 00 00 00 00 00 6A 01 00 00 00 00 00 00 6B 01 00 00 00 00 00 00 6C 01 00 00 00 00 00 00 6D 01 00 00 00 00 F8 08 E8 2B 10 10 20 20 40 40 80 B8 01 00 00 00 00 00 00 71 01 00 00 00 00 00 00 72 01 00 00 00 00 00 00 73 01 00 00 00 00 00 00 74 01 00 00 00 00 00 00 75 01 00 00 00 00 00 00 76 01

> C4 02 00 00 00 00 00 00
< 00 00 00 00 00 00 77 01 00 00 00 00 00 00 78 01 00 00 00 00 00 00 79 01 00 00 00 00 00 00 7A 01 00 00 00 00 00 00 7B 01 00 00 00 00 00 00 7C 01 00 00 00 00 00 00 7D 01 00 00 00 00 00 00 7E 01 00 00 00 00 00 00 7F 01 00 00 00 00 00 00 80 01 00 E0 02 02 04 04 48 2C 10 10 20 20 40 40 80 B0 40 40 80 80 00 00 00 84 01 00 00 00 00 00 00 85 01 00 00 00 00 00 00 86 01 00 00 00 00 00 00 87 01 00 00 00 00 00 00 88 01 00 00 00 00 00 00

> C5 02 00 00 00 00 00 00
< 89 01 00 00 00 00 00 00 8A 01 00 00 00 00 00 00 8B 01 00 00 00 00 00 00 8C 01 00 00 00 00 00 00 8D 01 00 00 00 00 00 00 8E 01 00 00 00 00 00 00 8F 01 00 00 00 00 00 00 90 01 00 00 00 00 00 00 91 01 00 00 00 00 00 00 92 01 00 00 00 00 00 00 93 01 00 00 00 00 00 00 94 01 00 00 00 00 00 00 95 01 00 00 FC 10 20 20 40 59 20 20 40 40 80 80 00 98 01 00 00 00 00 00 00 99 01 00 00 00 00 00 00 9A 01 00 00 00 00 00 00 9B 01 00 00 00 00 00 00 9C 01 00 00 00 00 00 00 9D 01 00 00 00 00 00 00 9E 01 00 00 00 00 00 00 9F 01 00 00 00 00 00 00 A0 01 00 00 00 00 00 00 A1 01 00 00 00 00 00 00 A2 01 00 00 00 00 00 00 A3 01 00 00 00 00 00 00 A4 01 00 00 00 00 00 00 A5 01 00 00 00 00

> D4 02 00 00 00 00 00 00
< D4 02 00 00 00 00 00 00

> D5 02 00 00 00 00 00 00
< D5 02 00 00 00 00 00 00

> D6 02 00 00 00 00 00 00
< D6 02 00 00 00 00 00 00

> D7 02 00 00 00 00 00 00
< D7 02 00 00 00 00 00 00

> D8 02 00 00 00 00 00 00
< D8 02 00 00 00 00 00 00

the > represents send and < represents received.

I applied this patch serial: imx: Prevent TX buffer PIO write when a DMA has been started · torvalds/linux@514ab34 · GitH... 

but it doesn't have any effect.

What might be causing this?

[sujay1 · Accepted solution]

This Issue was solved by adding patches found in:

[PATCH 1/7] serial: imx: only set DMA rx-ing when DMA starts 

[ceggers1]

Hi Sujay,

RS-485 networks require termination and an idle state biasing network. At least simple receivers my not be "fault tolerant" and my receive noise when the other side is not sending (idle line).

Regards

Christian

[sujay1]

Hi Christian,

Can you specify how to set up an idle state biasing network?

[ceggers1]

http://www.ti.com/lit/an/slyt324/slyt324.pdf 

[igorpadykov]

Hi Sujay

one can try to disable dma, to check if it not caused by dma.

Re: [PATCH] serial: imx: disable DMA for RS-485 on i.MX6 SMP - Fabio Estevam 

serial: imx: half-duplex RS485 operation with RTS active low - Patchwork 

Also one can try with nxp linux from source.codeaurora.org/external/imx/linux-imx  repository
linux-imx - i.MX Linux kernel 

Best regards
igor
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