The examples I've seen ( 1, 2 ) all assume a "modern" Raspberry Pi with a 40-pin GPIO connector.
If you want to use a Raspberry Pi 1 (26-pin GPIO), you need to pass -r, -c and -d to the flash_cc2531 tools, based on how you want to wire things (I'm using GPIO.3->Reset, GPIO.4->DC, GPIO.5->DD).
Check the example/pictures below.
root@octopi:~# gpio readall