--
-- file         : ps2.jal
-- author       : Carlos Alfaro
-- date         : 14-DEC-2000
-- purpose      : asynchronous PS/2 serial IO routines for host
-- includes     : jpic, ps2p
--
-- Copyright (C) 2000 Carlos Alfaro
--
-- This library is free software; you can redistribute it and/or
-- modify it under the terms of the GNU Library General Public
-- License as published by the Free Software Foundation; either
-- version 2 of the License, or (at your option) any later version.
--
-- This library is distributed in the hope that it will be useful,
-- but WITHOUT ANY WARRANTY; without even the implied warranty of
-- MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
-- Library General Public License for more details.
-- 
-- You should have received a copy of the GNU Library General Public
-- License along with this library; if not, write to the
-- Free Software Foundation, Inc., 59 Temple Place - Suite 330,
-- Boston, MA  02111-1307, USA.
--

-- required libraries
include jpic

-- the communication line settings
include ps2p

procedure ps2_wait_clock_low is
  while (ps2_clock_pin) loop end loop
end procedure

procedure ps2_wait_clock_high is
  while !(ps2_clock_pin) loop end loop
end procedure

-- send a bit
procedure ps2_send_bit (bit in val) is
  if val then
    ps2_data_direction = input
  else
    ps2_data_direction = output
    ps2_data_pin = low
  end if
  ps2_wait_clock_low
  ps2_wait_clock_high
end procedure

-- receive a bit
function ps2_read_bit return bit  is
  var bit val
  val = ps2_data_pin
  ps2_wait_clock_high
  ps2_wait_clock_low
  return val
end function

-- send a byte
procedure ps2_send( byte in x ) is
  var bit current_bit at x : 0
  var bit parity
  ps2_clock_direction = output
  ps2_data_direction = output

  -- seize clock control
  ps2_clock_pin = low
  -- wait for abot 60 us
  for 0xFF loop
  end loop
  ps2_data_pin = low
  -- listen to device
  ps2_clock_pin = high
  ps2_clock_direction = input
  ps2_wait_clock_low

  -- send the 8 data bits
  parity = high
  for 8 loop
    parity = parity ^ current_bit
    ps2_send_bit(current_bit)
    x = x >> 1
  end loop

  -- send parity bit
  ps2_send_bit(parity)

  -- disregard ACK
  ps2_data_direction = input
  ps2_read_bit
end procedure

procedure ps2'put( byte in x ) is
   ps2_send( x )
end procedure

-- receive a bit
procedure ps2_receive( byte out x ) is
  var bit current_bit at x : 7
  ps2_clock_direction = input
  ps2_data_direction = input

  -- wait for device to seize clock
  ps2_wait_clock_low

  -- disregard start bit
  ps2_read_bit

  -- get the 8 data bits
  for 8 loop
    x = x >> 1
    current_bit = ps2_read_bit
  end loop

  -- disregard parity and stop
  ps2_read_bit    -- parity
  ps2_read_bit    -- stop
end procedure

function ps2'get return byte is
  var byte x
  ps2_receive( x )
  return x
end function

function ps2_poll( byte out x ) return bit is 
  if ps2_clock_pin then
    ps2_receive (x)
    return true
  end if
   return false
end function