AT commands in a for loop

Question

I am trying to execute AT commands from a Nordic NRF52. I am using the Nordic UART module with a built-in function called app_uart_put(uint8_t byte) to put AT commands on the UART. The node that receiving the AT commands is a EE-NBIoT module and it triggers on a postfix \r\n. When I run the following code, I get OK.

while (app_uart_put('A') != NRF_SUCCESS);
while (app_uart_put('T') != NRF_SUCCESS);
while (app_uart_put('+') != NRF_SUCCESS);
while (app_uart_put('C') != NRF_SUCCESS);
while (app_uart_put('F') != NRF_SUCCESS);
while (app_uart_put('U') != NRF_SUCCESS);
while (app_uart_put('N') != NRF_SUCCESS);
while (app_uart_put('=') != NRF_SUCCESS);
while (app_uart_put('1') != NRF_SUCCESS);
while (app_uart_put('\r') != NRF_SUCCESS);
while (app_uart_put('\n') != NRF_SUCCESS);

But I want to make a more reusable code, so I wrote the following writeCommand function.

void writeCommand(char cmd[])
{   
 while (app_uart_put('A') != NRF_SUCCESS);
 while (app_uart_put('T') != NRF_SUCCESS);
 while (app_uart_put('+') != NRF_SUCCESS);

 uint8_t i;
 for(i = 0; cmd[i] != '\0'; i++){
     while (app_uart_put(cmd[i]) != NRF_SUCCESS);
 }

 while (app_uart_put('\r') != NRF_SUCCESS);
 while (app_uart_put('\n') != NRF_SUCCESS);
 nrf_delay_ms(100);
}

When I run this function as shown below, I get ERROR.

char cmd[] = "CFUN=1";
nrf_delay_ms(1000);
writeCommand(cmd);

Why does not this work? When I look at the outgoing commands, they are equal.

Is it correct that the first snippet sends `AT+CFUN=1` and the second sends `AT+CGATT=1`? — mch, Jul 05 '18 at 09:59
The EE-NBIoT module responds with ERROR to the AT command. It does not say what's wrong, but it just does not accept the command — Lars Erik Tiset Skraastad, Jul 05 '18 at 10:00
I would guess, that the error is outside the context you provide us. Maybe something is written to the uart before you call writecommand(): You could try and send `\r\n` first before sending your command. — Ctx, Jul 05 '18 at 10:04
thank you @Ctx! it seems that the `\r\n` in front of the command that caused the problem — Lars Erik Tiset Skraastad, Jul 05 '18 at 10:29
Have you heard of arrays? Use one to store your command string! — Eugene Sh., Jul 05 '18 at 17:57

score 0 · Answer 1 · edited Jun 20 '20 at 09:12

Start by acquiring a large A3 sheet of paper, find a red pen and write 1000 times

I will never use nrf_delay_ms as a substitute for reading and parsing responses from a modem.

I will never use nrf_delay_ms as a substitute for reading and parsing responses from a modem.

I will never use nrf_delay_ms as a substitute for reading and parsing responses from a modem.

I will never use nrf_delay_ms as a substitute for reading and parsing responses from a modem.

I will never use nrf_delay_ms as a substitute for reading and parsing responses from a modem.

...

I had a brief look at the AT command documentation for U-Blox Sara N210, and it seems decent although a bit brief on the introduction part. I suggest reading the V.250 specification first because that is much more thorough. So after writing your 1000 sentences, read this answer, first following the instructions regarding V.250, and then implement something along the given code structure of how to properly handle AT command command/response text.

Of course the first part was meant to be funny, but I am dead serious about the rest; you have some huge AT command knowledge "holes" you must fill. You will not be able have reliable communication until you do. It should not be very difficult, but it will require some effort.

AT commands in a for loop

1 Answers1