
pr_init("/dev/ttyS0")
  initialize port and verify device is connected

pr_close()
  close all serial ports

pr_check()
  re-verify device is connected

pr_reinit()
  reinitialize camera

pr_picture()
  take picture

value = pr_get(register)
  get single register value

value = pr_set(register, value)
  set single register value, then read it back and return it

data = pr_download(num, addr)
  initialize and download num bytes starting at address addr and return them
  addr defaults to 0 if not specified.

Low-level internal helper routines:

pr_flush()
  verify serial port object and flush serial data

