EasyLink createpacket() function

If you want to change the length byte (PKTLEN) you should change the #define PKTLEN 30 and not the txBuffer[0]. The reason for this is that you PKTLEN is used to set the size of the txBuffer and the size of txBuffer is again used to determine how many bytes should be written to the TXFIFO.

Note that for this example 1 < PKTLEN < 126.

Siri

First, thanks for the reply.

I know that changing the PKTLEN value I can change the length of the packet, but my idea is not modify the length, what I want is to modify the content of the packet, not the length, but I tried to change the first line of the createpacket() function and it doesn't work, it just send 4 packets instead of infinite number, ie, i change the first byte of the txBuffer and it doesn't work. Does anyone know why?

Thanks

If you are changing the first line in the createPacket function you are messing with the length as the length is the first thing you write to the txBuffer.

txBuffer[0] = PKTLEN;                           // Length byte

txBuffer[1] = (uint8) (packetCounter >> 8);     // MSB of packetCounter

txBuffer[2] = (uint8)  packetCounter;           // LSB of packetCounter

.

.

.

It would be helpful if you could show your modified code so that we can figure out what is going on.

Siri

Sorry for the late answer.

my function createpacket is:

/*****************************************************************************/
static void createPacket(uint8 txBuffer[]) {
    uint8 i;
    txBuffer[0] =0x08;                           // Length byte
   
    // Fill rest of buffer with random bytes
    for(i = 1; i < (PKTLEN + 1); i++) {
        txBuffer[i] = (uint8)i;
    }
}

/******************************************************************************/

and the PKTLEN is 10.

I am just trying to modify the content of the txBuffer, but I don't know why i have to send first the PKTLEN.

Thanks in advance

If you set PKTLEN to 10 your txBuffer will be 11 bytes long since

// Initialize packet buffer of size PKTLEN + 1

uint8 txBuffer[PKTLEN+1] = {0};

The packet you create in your createPacket function will look like this:

txBuffer[0] = 0x08

txBuffer[1] = 0x01

txBuffer[2] = 0x02

txBuffer[3] = 0x03

txBuffer[4] = 0x04

txBuffer[5] = 0x05

txBuffer[6] = 0x06

txBuffer[7] = 0x07

txBuffer[8] = 0x08

txBuffer[9] = 0x09

txBuffer[10] = 0x0A

You will be writing 11 bytes to the TXFIFO since sizeof(txBuffer) is used as an argument to the cc112xSpiWriteTxFifo function

// Write packet to TX FIFO

cc112xSpiWriteTxFifo(txBuffer, sizeof(txBuffer));

Since the radio is configured for variable packet length mode and you are writing 0x08 as the first byte to the TXFIFO the following will be sent on the air:

0x08, 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07, 0x08

This mean that there will be two bytes left in the TXFIFO:

0x09 and 0x0A

Next time you write your packet to the FIFO this will be the content in the TXFIFO:

0x09, 0x0A, 0x08, 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07, 0x08

0x09 will now be interpreted as the length byte and you will send the following on the air:

0x09, 0x0A, 0x08, 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07

0x08 will then be left in the FIFO.

As you understand it is necessary that the length (first byte in the FIFO) matches the length of the payload you want to send.

If you want your length byte to be 0x08 you should only write 9 bytes in total to the FIFO.

If you want to send the following packet

txBuffer[0] = 0x08

txBuffer[1] = 0x01

txBuffer[2] = 0x02

txBuffer[3] = 0x03

txBuffer[4] = 0x04

txBuffer[5] = 0x05

txBuffer[6] = 0x06

txBuffer[7] = 0x07

txBuffer[8] = 0x08

txBuffer[9] = 0x09

txBuffer[10] = 0x0A

you must reconfigure the radio to use fixed packet length mode and set the packet length to 11.

Siri