portio

---

portio is another example of me saying "I wonder if I can get this done in haskell." In my efforts to learn the language I look for any excuse to use it.

portio is for manipulating bits of memory mapped IO. It takes 3 arguments: an address containing the bit to change or read, the index of the bit itself (0 based), and the value to set that bit to.

I had the need to read and write GPIO ports on a PC designed for use in vehicles. These units have custom IO ports starting at address 0xee0. So, for example, to test if ignition is turned on or not, one may read 0xee0 and pay attention to the value for bit 2 (the third bit):

portio -a 0xee0 -b2 -v off

Note that in this example, the bit in question is read only so setting to something has no effect. portio will just output the value that it read from the port. It will indicate that it is writing a byte with the specified bit cleared. It can't modifiy a read-only bit though.

Command line args

portio -a <address> -b <bit number> -v <on|off>
  -a   --address=  The address to read or write to
  -b   --bit=      The bit to write
  -v   --value=    The value to write
  -V   --version   Print version information
  -h   --help      Print this usage information

To set a bit, value may be true, yes, on, or high. Any other value for the value parameter will clear the bit.

Compiling

ghc -o portio Main.hs options.hs --make

OR jump into the project dir and issue cabal install

Complications

portio makes use of System.Posix.IO.ByteString, however there are two modules with this name: one is in the package unix, and the other is in the package unix-bytestring. In order to indicate which System.Posix.IO.ByteString I wanted, I had to cabal install unix-bytestring and put the following in my code:

{-# LANGUAGE PackageImports #-}

module Main where

import qualified "unix-bytestring" System.Posix.IO.ByteString as BSIO