# #############################################################################
#
# Copyright (c) 2000-2001 by Wayne C. Gramlich & William T. Benson.
# All rights reserved.
#
# Permission to use, copy, modify, distribute, and sell this software
# for any purpose is hereby granted without fee provided that the above
# copyright notice and this permission are retained.  The author makes
# no representations about the suitability of this software for any purpose.
# It is provided "as is" without express or implied warranty.
#
# This is the code that implements the InOut4 RoboBrick.  Basically
# it just waits for commands that come in at 2400 baud and responds
# to them.  See
#
#   http://web.gramlich.net/projects/robobricks/inout4/index.html
#
# for more details.
#
# #############################################################################

processor pic12c509 cp=off wdte=off mclre=off fosc=intrc

# define processor constants	
constant clock_rate 4000000						
constant clocks_per_instruction 4
constant instruction_rate clock_rate / clocks_per_instruction
				
# define serial communication control constants
constant baud_rate 2400
constant instructions_per_bit instruction_rate / baud_rate
constant delays_per_bit 3
constant instructions_per_delay instructions_per_bit / delays_per_bit

register osccal 5
constant osccal_unit 0x10

constant inout_bit0 0
constant inout_bit1 1
constant inout_bit2 2
constant serial_in_bit 3
constant inout_bit3 4
constant serial_out_bit 5

constant inout_mask0 (1 << inout_bit0)
constant inout_mask1 (1 << inout_bit1)
constant inout_mask2 (1 << inout_bit2)
constant inout_mask3 (1 << inout_bit3)
constant serial_in_mask (1 << serial_in_bit)
constant serial_out_mask (1 << serial_out_bit)
constant io_mask 0xf

constant inout_mask (inout_mask0 | inout_mask1 | inout_mask2 | inout_mask3)
constant serial_mask (serial_in_mask | serial_out_mask)

# define port bit assignments
port porta a bits_and_byte read_write_manual
pin inout0 porta inout_bit0 read_write_manual
pin inout1 porta inout_bit1 read_write_manual
pin inout2 porta inout_bit2 read_write_manual
pin inout3 porta inout_bit3 read_write_manual
pin serial_in porta serial_in_bit read_only
pin serial_out porta serial_out_bit write_only

string_constants {
    id = 1, 0, 19, 0, 0, 0, 0, 0, 0r'16', 7, 0s'InOut4A', 15, 0s'Gramlich&Benson'
}
constant id_size 8 + 16 + 1 + 7 + 1 + 15

bank 0

global inputs byte
global complement byte
global direction byte
global outputs byte

# Interrupt masks:
global interrupt_enable bit
global interrupt_pending bit
global receiving bit
global falling byte
global high byte
global low byte
global raising byte
    
# For now put all the smaller routines first so that they can live
# within the first 256 bytes of main memory.  The PIC12C5xx chips
# can only call routines that are within the first 256 bytes (i.e.
# the first half) of the code page.

bank 0

procedure delay {
    arguments_none
    returns_nothing
    uniform_delay instructions_per_delay

    # This procedure will delay for one third of a bit time.

    variable current byte
    variable changed byte
    variable previous byte
    variable not_current byte

    # Kick the dog:
    watch_dog_reset

    # Setup for interrupts:
    previous := current
    # Read the I/O port once:
    inputs := porta
    inputs := inputs | (inputs >> 1) & 8
    current := inputs ^ complement
    not_current := current ^ 0xf
    changed := inputs ^ previous

    # See about triggering the interrupt_pending flag:
    if ((low & not_current) | (high & current) | (changed & current & raising) | (changed & not_current & falling) != 0) {
	interrupt_pending := 1
    }

    # Send an interrupt if interrupts are enabled:
    if (interrupt_pending && interrupt_enable) {
	# Shove serial out to low:
	serial_out := 0
    }
}	     

procedure get_byte {
    arguments_none

    returns byte

    # Wait for a character and return it.

    # The get_byte() procedure only waits for 9-2/3 bits.  That
    # way the next call to get_byte() will sychronize on the start
    # bit instead of possibly starting a little later.

    variable count byte
    variable char byte

    # Wait for start bit:
    receiving := 1
    while (serial_in) {
	call delay()
    }

    # Clear interrupts and interrupt pending:
    interrupt_enable := 0

    # Skip over start bit:
    call delay()
    call delay()
    call delay()

    # Sample in the middle third of each data bit:
    char := 0
    count_down count 8 {
	call delay()
        char := char >> 1
        if (serial_in) {
            char := char | 0x80
        }
	call delay()
	call delay()
    }

    # Skip over 2/3's of stop bit:
    call delay()
    call delay()

    return char
}

procedure send_byte {
    argument char byte
    returns_nothing

    # Send {char} to {tx}:

    variable count byte

    # {receiving} will be 1 if the last get/put routine was a get.
    # Before we start transmitting a response back, we want to ensure
    # that there has been enough time to turn the line line around.
    # We delay the first 1/3 of a bit to pad out the 9-2/3 bits from
    # for get_byte to 10 bits.  We delay another 1/3 of a bit just
    # for good measure.  Technically, the second call to delay()
    # is not really needed.
    if (receiving) {
	receiving := 0
	call delay()
	call delay()
    }

    # Send the start bit:
    serial_out := 0
    call delay()
    call delay()
    call delay()

    # Send the data:
    count_down count 8 {
	serial_out := char@0
	char := char >> 1
	call delay()
	call delay()
	call delay() 
    }

    # Send the stop bit:
    serial_out := 1
    call delay()
    call delay()
    call delay()
}

procedure update_outputs {
    arguments_none
    returns_nothing

    # This procedure will update the output bits:
    
    variable mask byte
    variable temp byte

    mask := (direction << 1) & 0x10 | direction & 7 | serial_in_mask
    assemble {
	tris 6
    }
    temp := porta & (mask | serial_mask)
    mask := mask ^ 0x17
    porta := temp | ((outputs << 1) | outputs) & mask
}

origin 0x200
bank 1

procedure bit_to_mask {
    argument bit byte
    returns byte

    # Convert low order 2-bits of {bit} to a mask.

    variable mask byte

    bit := bit & 3
    mask := 1
    while (bit != 0) {
	mask := mask << 1
	bit := bit - 1
    }
    return mask
}

# The main routine can span the 256 byte boundary:

procedure main {
    arguments_none
    returns_nothing

    variable command byte
    variable glitch byte
    variable id_index byte
    variable result byte

    # Let ROOT=http://web.gramlich.com/projects/robobricks .
    # For InOut4A specific commands see:
    #   ROOT/InOut4/rev_a/index.html
    # For shared commands see:
    #   ROOT/specifications.html#Software_Protocol
    # For shared interruptcommands see:
    #   ROOT/specifications.html#Interrupts

    # Set the direction:
    direction inout0 read
    direction inout1 read
    direction inout2 read
    direction inout3 read
    outputs := 0
    direction := 0xff
    interrupt_enable := 0
    interrupt_pending := 0
    falling := 0
    high := 0
    low := 0
    raising := 0
    glitch := 0
    id_index := 0
    loop_forever {
	# Wait for a command:
	command := get_byte()

	# Dispatch on command:
	switch (command >> 6) {
	  case 0 {
	    # Command = 00xx xxxx:
	    switch (command >> 3) {
	      case 0 {
		# Command = 0000 0xxx:
		switch (command & 7) {
		  case 0 {
		    # Read Inputs (Command = 0000 0000):
		    call send_byte(inputs ^ complement)
		  }
		  case 1 {
		    # Read Complement Mask (Command = 0000 0001):
		    call send_byte(complement)
		  }
		  case 2 {
		    # Read Low Mask (Command = 0000 0010):
		    call send_byte(low)
		  }
		  case 3 {
		    # Read High Mask (Command = 0000 0011):
		    call send_byte(high)
		  }
		  case 4 {
		    # Read Raising Mask (Command = 0000 0100):
		    call send_byte(raising)
		  }
		  case 5 {
		    # Read Falling Mask (Command = 0000 0101):
		    call send_byte(falling)
		  }
		  case 6 {
		    # Read Direction Mask (Command = 0000 0110):
		    call send_byte(direction)
		  }
		  case 7 {
		    # Read Outputs (Command = 0000 0111):
		    call send_byte(outputs)
		  }
		}
	      }
	      case 1 {
		# Command = 0000 1xxx:
		switch (command & 7) {
		  case 0 {
		    # Read Raw (Command = 0000 1000):
		    call send_byte(inputs)
		  }
		  case 1 {
		    # Set Complement Mask(Command = 0000 1001):
		    complement := get_byte() & io_mask
		  }
		  case 2 {
		    # Set High Mask (Command = 0000 1010):
		    high := get_byte() & io_mask
		  }
		  case 3 {
		    # Set Low Mask (Command = 0000 1011):
		    low := get_byte() & io_mask
		  }
		  case 4 {
		    # Set Raising Mask (Command = 0000 1100):
		    raising := get_byte() & io_mask
		  }
		  case 5 {
		    # Set Falling Mask (Command = 0000 1101):
		    falling := get_byte() & io_mask
		  }
		  case 6 {
		    # Set Direction Mask (Command = 0000 1110):
		    direction := get_byte() & io_mask
		    call update_outputs()
		  }
		  case 7 {
		    # Set Outputs (Command = 0000 1111):
		    outputs := get_byte() & io_mask
		    call update_outputs()
		  }
		}
	      }
	      case 2 {
		# Command = 0001 0xxx:
		if (command@2) {
		    # Bit Set (Command = 0001 01bb):
		    outputs := outputs | bit_to_mask(command)
		} else {
		    # Bit Clear (Command = 0001 00bb):
		    outputs := outputs & (bit_to_mask(command) ^ io_mask)
		}
	      }
	      case 3 {
		# Command = 0001 1xxx:
		if (command@2) {
		    # Bit Read (Command = 0001 11bb):
		    result := 0
		    if (outputs & bit_to_mask(command) != 0) {
			result := 1
		    }
		    call send_byte(result)
		} else {
		    # Bit Toggle (Command = 0001 10bb):
		    outputs := outputs ^ bit_to_mask(command)
		}
	      }
	      default 7 {
		# Undefined commands; do nothing:
	      }
	    }
	  }
	  case 1 {
	    # do nothing (Command = 01xx xxxx):
	  }
	  case 2 {
	    # Do nothing (Command = 10xx xxxx):
	  }
	  case 3 {
	    # Command = 11xx xxxx:
	    switch ((command >> 3) & 7) {
	      case 0, 1, 2, 3, 4 {
		# Command = 1100 xxxx or 1110 0xxx:
		# Do nothing:
	      }
	      case 5 {
		# Read Interrupt Bits (Command = 1110 1111):
		if ((command & 7) = 7) {
		    # Return Interrupt Bits:
		    result := 0
		    if (interrupt_enable) {
			result := result | 2
		    }
		    if (interrupt_pending) {
			result := result | 1
		    }
		    call send_byte(result)
		}
	      }
	      case 6 {
		# Shared Interrupt commands (Command = 1111 0xxx):
		switch (command & 7) {
		  case 0, 1, 2, 3 {
		    # Set interrupt bits (Command = 1111 10ep):
		    interrupt_enable := command@1
		    interrupt_pending := command@0
		  }
		  case 4, 5 {
		    # Set Interrupt Pending (Command = 1111 110p):
		    interrupt_pending := command@0
		  }
		  case 6, 7 {
		    # Set Interrupt Enable (Command = 1110 111e):
		    interrupt_enable := command@0
		  }
		}
	      }
	      case 7 {
		# Shared commands (Command = 1111 1xxx):
		switch (command & 7) {
		  case 0 {
		    # Clock Decrement (Command = 1111 1000):
		    osccal := osccal - osccal_unit 
		  }
		  case 1 {
		    # Clock Increment (Command = 1111 1001):
		    osccal := osccal + osccal_unit
		  }
		  case 2 {
		    # Clock Read (Command = 1111 1010):
		    call send_byte(osccal)
		  }
		  case 3 {
		    # Clock Pulse (Command = 1111 1011):
		    call send_byte(0)
		  }
		  case 4 {
		    # ID Next (Command = 1111 1100):
		    if (id_index >= id.size) {
			id_index := 0
		    }
		    call send_byte(id[id_index])
		    id_index := id_index + 1
		    if (id_index >= id_size) {
			id_index := 0
		    }
		  }
		  case 5 {
		    # ID Reset (Command = 1111 1101):
		    id_index := 0
		  }
		  case 6 {
		    # Glitch Read (Command = 1111 1110):
		    call send_byte(glitch)
		    glitch := 0
		  }
		  case 7 {
		    # Glitch (Command = 1111 1111):
		    if (glitch != 0xff) {
			glitch := glitch + 1
		    }
		  }
		}
	      }
	    }
	  }
	}
    }
}