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pavankc 06-25-2012 05:36 AM

RS485 with Linux 2.6.34
Hi All,

I am working with RS485 for sending a few frames to a RET (Remote Electrical Tilt) unit. This all works beautifully on linux 2.6.25 but with Linux 2.6.34, the response from the RET is not complete. I mean I receive an incomplete frame. The first and the last bytes are missing from the frame.

I am making sure that the bus is released as soon as the frame is sent to the RET unit. Is there a delay in releasing the bus which is causing this?

Any ideas?


jefro 06-25-2012 10:12 PM

Do you have a black box for this 485 or are you just trying to get by with 232? Or do you have a 485 card?

I'd like to know the speed too and any other settings used that did work and now do not.

pavankc 06-26-2012 09:59 AM

Hi jefro,

Thanks a lot for the reply. I have solved it now. When the 34 kernel booted up, it detected and initilaised the 16550 UART (which has a 1 byte FIFO) and not the 16550A UART (which has a 16 byte FIFO). So when frames were sent to ttyS1, 16550 UART was being used and not the 16550A UART.
This made things slower and also resulted in loss of bytes. Now I have made sure that 16550A is detected and initialised. So its all working now. :-)


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