AnsweredAssumed Answered

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

Question asked by Sujay S on Feb 13, 2020
Latest reply on Feb 13, 2020 by igorpadykov

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?

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