SPI Sniffer Firmware

' Set up the FIFO for data going out the serial port.
const FIFOSIZE as byte = 40

dim fifohead, fifotail as byte
dim fifoempty, fifofull as boolean
dim fifo as byte[FIFOSIZE]

' fifodatawaiting()
sub function fifodatawaiting as boolean
  if fifoempty then
    result = false
  else
    result = true
  end if
end sub

' writefifo()
sub procedure writefifo
  dim j as byte
  j = 0 ' If the buffer is empty, read 0.
  if fifoempty = false then ' As long as the buffer isn't empty...
    j = fifo[fifohead] ' Read in the contents of the head of the FIFO.
    fifo[fifohead] = 0 ' Set the previously read byte to 0. Destructive read.
    fifofull = false ' Since we've read data, the buffer can no longer be full.
    inc(fifohead) ' Move the head pointer to the next place.
    if fifohead = FIFOSIZE then ' If the head is now greater than buffer size,
      fifohead = 0 ' move it back to place 0.
    end if
    if fifohead = fifotail then ' If the head and tail are in the same place,
      fifoempty = true ' the buffer can be considered to be empty.
    end if
  end if
  usart_write(j) ' Write the FIFO out the serial port.
end sub

' interrupt()
'sub procedure interrupt
'end sub

main:

memset(@fifo,0,FIFOSIZE) ' Fill the FIFO with zeros.
fifohead = 0 ' Head is at 0.
fifotail = 0 ' Tail is at 0.
fifoempty = true ' FIFO is empty.
fifofull = false ' FIFO is not full.
usart_init(19200) ' Set the USART to 19.2K
spi_init_advanced(slave_ss_dis,data_sample_middle,clk_idle_low,low_2_high)