Raspberry Pi Zero shield with the SX1255 RF transceiver chip.

Sample Raspberry Pi code for SX1255 control can be found here.
I2S slave overlay is required. Sample rate for both RX and TX is 125kHz.

RX/TX frequency setting:

./sx1255-spi 435000000 438000000

arecord -t raw -f S32_LE -r 192000 -c 2 --device="hw:0,1" | ./int_to_short | ./zmq-pub

In which int_to_short is a simple int to short format converter:

while(1)
{
  ioctl(STDIN_FILENO, FIONREAD, &rcvd);
  if(rcvd>0)
  {
    if(read(STDIN_FILENO, inp, rcvd)==rcvd)
    {
      for(int i=0; i<rcvd; i+=8)
      {
        memcpy(&out[i/2  ], &inp[i  +2], 2);
        memcpy(&out[i/2+2], &inp[i+4+2], 2);
      }

      write(STDOUT_FILENO, out, rcvd/2);
    }
  }
}

./zmq-sub 192.168.50.243:17018 | aplay -t raw -f S32_LE -r 192000 -c 2 --device="hw:0,0"

There are 2 demo flowgraphs available:

• cari_sx1255_rx_demo.grc
• cari_sx1255_multicarrier_tx_demo.grc

The RX demo also provides a set of sinc compensating FIR filter taps through the Decimating FIR Filter block.

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