ChibiOS Free Embedded RTOS

Hello,

I would like to include a gsm module into my project but i have an issue with a SerialDriver. Gsm module is connected to a stm32f4 via usart2 interface and it uses PA2 and PA3 pins for communication. When i send a command string to the gsm module everything works ok, the gsm module receives my command and it responds accordingly. The problem is that when i want to read the response i get an empty string, even if the response is clearly seen with a help of a logic analyzer. I have set a pin mode for PA2 and PA3 as an alternate function 7(according to a datasheet), output type pushpull, speed 50mhz and i also turned on pull up resistors.

What could be a problem?

If it is a nucleo board then PA2 and PA3 are connected to the STLink.

Giovanni

i'm using a stm32f4 discovery board. Datasheet for this board states that pins PA2 and PA3 are free pins.

It is possible that the RX signal is assigned to more than one pin, check board.h.

Giovanni

I checked a datasheet and i figured out that besides pin PA3, there is also a pin PD6 assigned to a usart2_rx. Pin PD6 has an alternate function 0 set in a board file.

You cannot assign the same function to multiple pins, probably that is the problem.

Giovanni

I connected only pins PA2 and PA3 with a usart2(alternate function 7). Pins such as PD6 and PD5 which can also be used for usart2 are not connected with usart2(they don't have an alternate function set). I am going to try a sdReadTimeout() function with a timeout set to one second and see if i am going to get a response back.

I tried to use usart3 instead of usart2 and the problem is still present. I tried to read a response with an sdReadTimeout() function into a buffer and noticed that the return value of the function is always 10. The content of a buffer is not a proper response value(\r\nOK\r\n) but a weird string which contains 10 ascii characters with an ordinal number 127.

I have no elements to provide support.

Giovanni

I successfully resolved a problem. The problem was that i forgot to set the number of stop bits in the cr2 register. Thank you for your help.