serial_rs485

What processor is this?

What software is this?

Hi Biser

processor: am3352
software: sdk6

Thank you

Hi Bernie,

delay_rts_before_send & delay_rts_after_send are delays that define the assertion of RTS (request to send) before & after sending data over the serial interface. They are part of the flow control (see Chapter 19 Universal Asynchronous Receiver/Transmitter (UART) in AM335x TRM). They are defined in milliseconds.
Check:
Documentation/serial/serial-rs485.txt
http://armbedded.eu/node/322
www.acmesystems.it
www.kernel.org/.../rs485.txt

Best Regards,
Yordan

Hi Yordan

Thanks your sharing, from your link, I realize that RTS is a signal to enable transmitter in RS485 mode, and needs delay before sending data, because transmitter is needed to be configured ( If I wrong, correct me! Thank you.), and what about delay_rts_after_send?  I will appreciate your direct. 

Again, this is a delay (in milliseconds) that points how much time after sending the data logic value of the rts will be sent. Both delays are used if needed. It is possible to set only delay_rts_before_send.

Best Regards,
Yordan

Hi Yordan

sorry

I know both of delay_before_send and delay_after_send is optional if I need,  Indeed, I just want to know, why rs485 send delays  of rts  if  I need?

Thank you. 

As I said they are used for flow control.
If you follow the code of oma-serial.c drive you will see that
rs485conf->delay_rts_before_send = rs485_delay[0];
rs485conf->delay_rts_after_send = rs485_delay[1];

The values of rs485_delay[x] are taken from device tree - rs485-rts-delay value (see Documentation/devicetree/bindings/serial/rs485.txt:

Required properties:
- rs485-rts-delay: prop-encoded-array <a b> where:
* a is the delay between rts signal and beginning of data sent in milliseconds.
it corresponds to the delay before sending data.
* b is the delay between end of data sent and rts signal in milliseconds
it corresponds to the delay after sending data and actual release of the line.

Those are needed to match the timings along the serial communication line.

Best Regards,
Yordan