# #############################################################################
#
# 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 LED4 RoboBrick.  Basically
# it just waits for commands that come in at 2400 baud and responds
# to them.  See
#
#   http://web.gramlich.net/projects/robobricks/thresh4/index.html
#
# for more details.
#
# #############################################################################

processor pic12c509 cp=off wdte=on 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

# For the 509, there are 4-bits of OSCCAL, for the 509A, 6-bits:
register osccal 5
constant osccal_unit 0x10

# Define port bit assignments:
port porta a bits_and_byte read_write_static
pin in0 porta 0 read_only
pin in1 porta 1 read_only
pin in2 porta 2 read_only
pin in3 porta 3 read_only
pin serial_in  porta 4 read_only
pin serial_out porta 5 write_only

string_constants {
    id = 1, 0, 19, 0, 0, 0, 0, 0, 0r'16', 11, 0s'Threshold4A', 15, 0s'Gramlich&Benson'
}

# Globals:
global complement byte
global receiving bit
global falling byte
global high byte
global low byte
global raising byte
global interrupt_enable bit
global interrupt_pending bit
    
# 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.

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 any interrupt being sent:
    serial_out := 1

    # 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 put_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 delay {
    arguments_none
    returns_nothing
    uniform_delay instructions_per_delay

    # This procedure will delay for 1/3 of a bit time.

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

    # Kick the dog:
    watch_dog_reset

    # Compute interrupt pending:
    previous := current
    current := (porta ^ 0xf ^ complement) & 0xf
    not_current := current ^ 0xf
    changed := current ^ previous
    if ((low & not_current) | (high & current) | (changed & current & raising) | (changed & previous & falling) != 0) {
	interrupt_pending := 1
    }

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

# The main routine can span the 256 byte boundary:

origin 0x200

procedure main {
    arguments_none
    returns_nothing

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

    # For Threshold4A specific commands see:
    #   http://web.gramlich.com/projects/robobricks/threshold4/rev_a/index.html
    # For shared commands see:
    #   http://web.gramlich.com/projects/robobricks/index.html#Software_Protocol
    # For shared interruptcommands see:
    #   http://web.gramlich.com/projects/robobricks/index.html#Interrupts

    # Initialize everything:
    interrupt_enable := 0
    interrupt_pending := 0
    falling := 0
    high := 0
    low := 0
    raising := 0
    glitch := 0
    id_index := 0

    # Loop waiting for commands:
    loop_forever {
	# Get a command byte:
	command := get_byte()

	# Dispatch on command:
	switch (command >> 6) {
	  case 0 {
	    # Command = 00xx xxxx:
	    switch ((command >> 3) & 7) {
	      case 0 {
		# Command = 0000 0xxx:
		switch (command & 7) {
		  case 0 {
		    # Read Inputs (Command = 0000 0000):
		    call put_byte((porta ^ 0xf ^ complement) & 0xf)
		  }
		  case 1 {
		    # Read Complement Mask (Command = 0000 0001):
		    call put_byte(complement)
		  }
		  case 2 {
		    # Read High Mask (Command = 0000 0010):
		    call put_byte(high)
		  }
		  case 3 {
		    # Read Low Mask (Command = 0000 0011):
		    call put_byte(low)
		  }
		  case 4 {
		    # Read Raising Mask (Command = 0000 0100):
		    call put_byte(raising)
		  }
		  case 5 {
		    # Read Falling Mask (Command = 0000 0101):
		    call put_byte(falling)
		  }
		  case 6 {
		    # Read Raw (Command = 0000 0110):
		    call put_byte((porta ^ 0xf) & 0xf)
		  }
		  default 7 {
		    # Undefined command; do nothing (Command = 0000 0111):
		  }
		}
	      }
	      case 1 {
		# Command = 0000 1xxx:
		# Do nothing:
	      }
	      case 2, 3 {
		# Set Complement Mask (Command = 0001 cccc):
		complement := command & 0xf
	      }
	      case 4, 5 {
		# Set High Mask (Command = 0010 hhhh):
		high := command & 0xf
	      }
	      case 6, 7 {
		# Set Low Mask (Command = 0011 llll):
		low := command & 0xf
	      }
	    }
	  }
	  case 1 {
	    # Command = 01xx xxxx:
	    switch ((command >> 4) & 3) {
	      case 0 {
		# Set Raising Mask (Command = 0100 rrrr):
		raising := command & 0xf
	      }
	      case 1 {
		# Set Falling Mask (Command = 0101 ffff):
		falling := command & 0xf
	      }
	      default 3 {
		# Command = 011x xxxx:
		# Do nothing:
	      }
	    }
	  }
	  case 2 {
	    # Command = 10xx xxxx:
	    # Do nothing:
	  }
	  case 3 {
	    # Command = 11xx xxxx:
	    switch ((command >> 3) & 7) {
	      case 5 {
		# Command = 1110 1xxx:
		if ((command & 7) = 7) {
		    # Return Interrupt Bits (Command = 1110 1111):
		    result := 0
		    if (interrupt_enable) {
			result := result | 2
		    }
		    if (interrupt_pending) {
			result := result | 1
		    }
		    call put_byte(result)
		}
	      }
	      case 6 {
		# Shared Interrupt commands.
		switch ((command >> 1) & 3) {
		  case 0, 1 {
		    # Set Interrupt Bits (Command = 1110 00ep):
		    interrupt_enable := command@1
		    interrupt_pending := command@0
		  }
		  case 2 {
		    # Set Interrupt Pending (Command = 1110 010p):
		    interrupt_pending := command@0
		  }
		  case 3 {
		    # Set Interrupt Enable (Command = 1110 011e):
		    interrupt_enable := command@0
		  }
		}
	      }
	      case 7 {
		# Shared commands (Command = 1111 1ccc):
		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 put_byte(osccal)
		  }
		  case 3 {
		    # Clock Pulse (Command = 1111 1011):
		    call put_byte(0)
		  }
		  case 4 {
		    # ID Next (Command = 1111 1100):
		    if (id_index >= id.size) {
			id_index := 0
		    }
		    call put_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 put_byte(glitch)
		    glitch := 0
		  }
		  case 7 {
		    # Glitch (Command = 1111 1111):
		    if (glitch != 0xff) {
			glitch := glitch + 1
		    }
		  }
		}
	      }
	    }
	  }
	}
    }
}