Hardware Flow control for serial communication

[mayurharge]

Hello,
I am using the STM32f103c series controller with GSM module. Sometimes Serial buffer of GSM is getting full and the communication is not happening as expected. During my search, I came across Hardware Flow control using RTS/CTS. As stm has dedicated H/W flow control pins [For UART 2 PA0:- CTS2 & PA1:-RTS2] is there any option available in board files to enable hardware flow control?
if yes please let me know how to enable it
if not then it would be really helpful if you can integrate this in next version.

Thanks

[fpistm]

HW flow control is not implemented.

[mayurharge]

Okay, thanks.

[mayurharge]

Hey are you going to implement this feature in future, also please give me some suggestions to implement by myself

[fpistm]

If I well remember it is based on how MBed implement UART. And if I well remember, flow control is also implemented on MBed side. So this could be a good starting point.

[mayurharge]

Thanks i will look into it

[fpistm]

@mayurharge
You could let this issue opened as a requested feature.
Do not hesitate to provide a PR if you get it up and running.

[arihantdaga]

@fpistm I saw this line in cores/arduino/stm32/uart.c

Arduino_Core_STM32/cores/arduino/stm32/uart.c

Line 272 in 7b48eff

huart->Init.HwFlowCtl = UART_HWCONTROL_NONE;

. Does making the HwFlowCtl to UART_HWCONTROL_CTS or UART_HWCONTROL_RTS is all thats required ? I am not sure yet, testing it. But if it works, I'll add this configuration using macros and make it user configurable...

[fpistm]

I guess you have also to init the RTS/CTS pin also.

[fpistm]

Just a quick thought if the buffer is full.
By default , the Rx and Tx buffer of the core is 64.

Arduino_Core_STM32/cores/arduino/HardwareSerial.h

Line 42 in bad5b56

#if !defined(SERIAL_TX_BUFFER_SIZE)

You can redefined them by adding a new file (Tab on Arduino IDE) named build_opt.h
Then in this file put:
-DSERIAL_RX_BUFFER_SIZE=256 -DSERIAL_TX_BUFFER_SIZE=256

Increasing only one of both works also but I advise to keep them aligned.

[mayurharge]

@fpistm I am already using the BUFFER_SIZE =256.
the need for me to use hardware flow control is that the slave device SIM800c is lagging behind over time
When I searched for this issue I figured out this

Flow control is very important for correct communication between the GSM engine and DTE.
For in the case such as a data or fax call, the sending device is transferring data faster than the
receiving side is ready to accept. When the receiving buffer reaches its capacity, the receiving
device should be capable to cause the sending device to pause until it catches up

This was mentioned in the datasheet of SIM800.