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

sujay1 — Thu, 13 Feb 2020 13:03:42 GMT

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 · GitHub

but it doesn't have any effect.

What might be causing this?

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

igorpadykov — Thu, 13 Feb 2020 23:53:07 GMT

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

ceggers1 — Fri, 21 Feb 2020 19:48:34 GMT

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

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

sujay1 — Tue, 25 Feb 2020 05:16:29 GMT

Hi Christian,

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

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

ceggers1 — Tue, 25 Feb 2020 05:24:19 GMT

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

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

sujay1 — Fri, 28 Feb 2020 13:09:16 GMT

This Issue was solved by adding patches found in:

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

topic Receiving junk data while running rs485 send and receive application on imx6dl in i.MX Processors

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

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

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

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

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

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