How to read nrf sniffer 4.1.0 serial data in C?

[Matthew C Clark]

I'm trying to work with Kismet's nrf51822 plugin that would allow kismet to read the nRF BLE sniffer 4.1.0 the same way Wireshark does.  Alas, theirs is C based and I don't seem to get the right data off my nRF51 DK reading its serial port in C the way the Wireshark plugin does.

Can I first validate I should be opening the /dev/ttyACM0 with 115200 N81 no flow control?  I'm basing that on the results

$ stty < /dev/ttyACM0
speed 115200 baud; line = 0;
intr = <undef>; quit = <undef>; erase = <undef>; kill = <undef>; eof = <undef>; start = <undef>; stop = <undef>; susp = <undef>; rprnt = <undef>; werase = <undef>; lnext = <undef>;
discard = <undef>; min = 0; time = 1;
-brkint -icrnl -imaxbel
-opost -onlcr
-isig -icanon -iexten -echo -echoe -echok -echoctl -echoke

[Amanda Hsieh]

Hi, 

The speed should be 1M (1000000). 

Flow control does not really matter since it is a virtual COM port. However, HW FC is on between the VCOM and the nRF COM. The argument provided to stty will not have any effect.

Regards,
Amanda

[Matthew C Clark]

Thanks, Amanda, I'll give that a try. If it helps, this is the code in kismet that attempts to open /dev/ttyACM0 where my nRF attaches.  If there are any settings you know that should be on/off, please let me know?

/* open for r/w but no tty */
localnrf->fd = open(device, O_RDWR | O_NOCTTY);

if (localnrf->fd < 0) {
    snprintf(msg, STATUS_MAX, "%s failed to open serial device - %s",
    localnrf->name, strerror(errno));
    return -1;
}

 /* save current serial port settings */
tcgetattr(localnrf->fd,&localnrf->oldtio);

/* clear struct for new port settings */
bzero(&localnrf->newtio,sizeof(localnrf->newtio)); 

/* set the baud rate and flags */
localnrf->newtio.c_cflag = localnrf->baudrate | CRTSCTS | CS8 | CLOCAL | CREAD;

/* ignore parity errors */
localnrf->newtio.c_iflag = IGNPAR;

/* raw output */
localnrf->newtio.c_oflag = 0;

/* newtio.c_lflag = ICANON; */

/* flush and set up */
tcflush(localnrf->fd, TCIFLUSH);
tcsetattr(localnrf->fd, TCSANOW, &localnrf->newtio);

return 1;

[Matthew C Clark]

Following up a bit, I managed to play with settings to get data across the line.  Though the serial read is still a bit wonky as I get varying buffer sizes (see below), it appears at least for the nRF51, you're using SLIP for packet coding?  The code looks for 0xAB (SLIP_START) and 0xBC (SLIP_END).  Is this correct?

buf_rx_len = 4 0xBC 0xAB 0x2B 0x0
buf_rx_len = 2 0x3 0xB6
buf_rx_len = 1 0x23
buf_rx_len = 3 0x2 0xA 0x1
buf_rx_len = 2 0x26 0x54
buf_rx_len = 3 0x0 0x0 0x39
buf_rx_len = 2 0xCB 0x5
buf_rx_len = 1 0xB
buf_rx_len = 4 0xD6 0xBE 0x89 0x8E
buf_rx_len = 1 0x0
buf_rx_len = 4 0x17 0x0 0xCA 0x91
buf_rx_len = 2 0x2F 0x85
buf_rx_len = 1 0x4A
buf_rx_len = 3 0x6C 0x2 0x1
buf_rx_len = 3 0x1A 0x2 0xA
buf_rx_len = 2 0xC 0xA
buf_rx_len = 1 0xFF
buf_rx_len = 3 0x4C 0x0 0x10
buf_rx_len = 2 0x5 0xA
buf_rx_len = 2 0x14 0x33
buf_rx_len = 2 0x3C 0x76
buf_rx_len = 3 0xF5 0x2B 0x92
buf_rx_len = 1 0xBC
buf_rx_len = 3 0xAB 0x2B 0x0

[Amanda Hsieh]

Hi, 

In the 4.1.0 release in the doc folder there is a sniffer_uart_protocol.txt document that you can use.

-Amanda

[Matthew C Clark]

Yes, I found that last night.  Right now my main issue is that when I try to read the fd via:

res = read(localnrf->fd, buf, 255);

I get the buffers of random lengths listed above.  I've not been able to find a simple C example that properly manages it.  Wireshark uses your python interface.