# #############################################################################
#
# Copyright (c) 2002-2003 by Wayne C. Gramlich and Bill 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 CompassDT1 RoboBrick.  Basically
# it just waits for commands that come in at 2400 baud and responds
# to them.  See
#
#   http://gramlich.net/projects/robobricks/compassdt1/index.html
#
# for more details.
#
# #############################################################################

processor pic16c505 cp=off wdte=on mclre=off fosc=intrc_no_clock

# 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
constant extra_instructions_per_bit 9
constant extra_instructions_per_delay extra_instructions_per_bit / delays_per_bit
constant delay_instructions instructions_per_delay - extra_instructions_per_delay

# Register definitions:

# Status register:
register status 3
bind c status@0
bind z status@2

# OSCCAL register:
register osccal 5
constant osccal_lsb 4

constant i2c_delay 3

# Define bit offsets:
constant d1_bit 5
constant d2_bit 4
constant d3_bit 3
constant d4_bit 2
constant d5_bit 1
constant d6_bit 0
constant scl_bit 0
constant sda_bit 1
constant freq_bit 2
constant serial_in_bit 3
constant serial_out_bit 4
constant trigger_bit 5

# Define pin assignments and directions:

port portb b bits_and_byte read_write_manual
port portc c bits_and_byte read_write_static
pin d1 portc d1_bit write_only
pin d2 portc d2_bit write_only
pin d3 portc d3_bit write_only	
pin d4 portc d4_bit write_only
pin d5 portc d5_bit write_only
pin d6 portc d6_bit write_only
pin scl portb scl_bit read_write_manual
pin sda portb sda_bit read_write_manual
pin trigger portb trigger_bit write_only
pin freq portb freq_bit write_only
pin serial_out portb serial_out_bit write_only
pin serial_in  portb serial_in_bit read_only

constant mask 0x1f
string_constants {
    id = 1, 0, 13, 1, 0, 0, 0, 0, 0r'16', 11, 0s'CompassDT1C', 15, 0s'Gramlich&Benson'
}

# Some globals: byte
global interrupt_enable bit
global interrupt_pending bit
global receiving bit

bank 1

global temporary byte
global glitch byte
global index byte

# Note that the 12-bit PIC's only have a 2-level deep stack.
# The code starts in the main procedure (located at the end of this code)
# The next level of procedure call is either get_byte or send_byte.
# Lastly, the lowest level of procedure call is delay.  It all fits,
# but just barely.

bank 0

procedure i2c_start {
    arguments_none
    returns_nothing

    # Invariant: SCL=OC & SDA=OC
    nop i2c_delay
    direction sda write
    nop i2c_delay
    direction scl write
    nop i2c_delay
    # Invariant: SCL=0V & SDA=0V
}

procedure i2c_restart {
    arguments_none
    returns_nothing

    nop i2c_delay
    direction sda read
    nop i2c_delay
    direction scl read
    nop i2c_delay
    direction sda write
    nop i2c_delay
    direction scl write
}

procedure i2c_stop {
    arguments_none
    returns_nothing

    # Invariant: SCL=0V & SDA=0V
    nop i2c_delay
    direction scl read
    nop i2c_delay
    direction sda read
    nop i2c_delay
    # Invariant: SCL=OC & SDA=OC
}

procedure i2c_get_byte {
    arguments_none
    returns byte

    # This procedure will wait for a byte to be received from
    # serial_in_bit.  It calls the delay procedure for all delays.

    variable count byte
    variable char byte

    # Invariant: SCL=0V & SDA=0V
    direction sda read
    count_down count 8 {
	char := char << 1

	nop i2c_delay
	direction scl read
	nop i2c_delay
	if (sda) {
	    char@0 := 1
	}
	direction scl write
	nop i2c_delay
    }

    # Clock in ACK bit:
    direction sda write
    nop i2c_delay
    direction scl read
    nop i2c_delay
    direction scl write
    nop i2c_delay

    # Invariant: SCL=0V & SDA=0V
    return char
}

procedure i2c_send_byte {
    argument data byte
    returns_nothing

    # Send {data} to compass using I2c:

    variable count byte

    # Invariant: SCL=0V & SDA=0V

    # Send 8-bits of data:
    count_down count 8 {
	if (data@7) {
	    direction sda read
	} else {
	    direction sda write
	}
	data := data << 1
	nop i2c_delay
	direction scl write
	nop i2c_delay
	direction sda read
	nop i2c_delay
    }

    # Clock in ACK bit:
    direction sda read
    nop i2c_delay
    direction scl read
    count := 255
    while (sda && count != 0) {
	count := count - 1
    }
    direction scl write
    count := 255
    while (!sda && count != 0) {
	count := count - 1
    }

    # Grab the SDA back again:
    direction sda write
    #Invariant: SCL=0V & SDA=0V
}

procedure get_byte {
    arguments_none
    returns byte

    # This procedure will wait for a byte to be received from
    # serial_in_bit.  It calls the delay procedure for all delays.

    variable count byte
    variable char byte

    # Why does the delay procedure wait for a third of bit?  Well, it
    # has to do with the loop immediately below.  If we catch the
    # start bit at the beginning of a 1/3 bit time, we will be
    # sampling data at approximately 1/3 of the way into each bit.
    # Conversely, if we catch the start near the end of a 1/3 bit
    # bit time, we will be sampling data at approximately 2/3 of the
    # way into each bit.  So, what this means is that our bit sample
    # times will be somewhere between 1/3 and 2/3 of bit (i.e. in
    # the middle of the bit.

    # It would be nice to tweak the code to shorter delay times
    # (1/4 bit, 1/5 bit, etc.) but then it gets too hard to get
    # the bookeeping done in the delay routine.  A 12-bit PIC
    # running at 4MHz (=1MIPS), only has 138 instructions available
    # for the delay routine when at 1/3 of bit.

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

    # Clear interrupt:
    # 1 cycle:
    serial_out := 1

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

    # Sample in the middle third of each data bit;
    # 1 cycle:
    char := 0
    # 2 cycles to set up loop:
    # 1+1+2 = 4
    nop extra_instructions_per_bit - 4
    count_down count 8 {
	call delay()
	# 2 cycles:
	char := char >> 1
	# 2 cycles:
	if (serial_in) {
	    char@7 := 1
	}
        call delay()
        call delay()
	# 3 cycles at end of loop:
	# 2+2+3 = 7
	nop extra_instructions_per_bit - 7
    }

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

origin 0x200
bank 1

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 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:
    # 1 cycle:
    serial_out := 0
    call delay()
    call delay()
    call delay()

    # 2 cycles to set up loop:
    # 1+2 = 3
    nop extra_instructions_per_bit - 3

    # Send the data:
    count_down count 8 {
	# 4 cycles:
	serial_out := char@0
	# 2 cycles:
	char := char >> 1
	call delay()
	call delay()
	call delay() 
	# 3 cycles at end of loop:
	# 4+2+3 = 9 = no NOP's needed:
    }

    # Send the stop bit:
    nop 1
    # 1 cycle
    serial_out := 1
    call delay()
    call delay()
    call delay()
    # 2 cycles for call/return
    # 2 cycles for argument
    # 1+2+2 = 5
    nop extra_instructions_per_bit - 5
}

procedure delay {
    arguments_none
    returns_nothing
    uniform_delay delay_instructions

    # This procedure delays 1/3 of a bit.

    # Kick the dog:
    watch_dog_reset
}

# The main procedure is loaded with switch statements.  On the 12-bit
# PIC's, switch statements have to live in the first 256 bytes of
# each code bank.  For this reason, we shove main into code bank 1.
# If we, try to put main in code bank 0, it pushes the first bytes
# of several routines out of the first 256 bytes, which is also a
# no-no of the 12-bit PIC's.

procedure main {
    arguments_none
    returns_nothing

    variable command byte
    variable temp byte

    # Initalize all of the globals:
    interrupt_enable := 0
    interrupt_pending := 0

    # Initialize remaining registers:
    glitch := 0
    index := 0

    # Set up the SCL bus:
    direction sda read
    direction scl read
    sda := 0
    scl := 0
    trigger := 0

    loop_forever {
	nop 40
	trigger := 0
	sda := 0
	scl := 0
	direction scl read
	direction sda read
	nop 60
	trigger := 1
	sda := 0
	scl := 0
	direction scl write
	direction sda write
    }

    # Process commands:
    loop_forever {	
	# Wait for command:
	#command := get_byte()
	command := 3

	# 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 {
		    # (Command = 0000 0000):
		    call send_byte(0xa4)
		    call i2c_start()
		    call i2c_send_byte(0xc0)
		    call i2c_send_byte(1)
		    call i2c_restart()
		    call i2c_send_byte(0xc1)
		    temporary := i2c_get_byte()
		    call i2c_stop()
		    call send_byte(temporary)
		    portc := temporary
		  }
		  case 1 {
		    # (Command = 0000 0001):
		    call send_byte(0xa5)
		    call i2c_start()
		    call i2c_send_byte(0xc0)
		    call i2c_send_byte(0)
		    call i2c_restart()
		    call i2c_send_byte(0xc1)
		    temporary := i2c_get_byte()
		    call i2c_stop()
		    call send_byte(temporary)
		  }
		  case 2 {
		    # (Command = 0001 0xxx):
		    call send_byte(2)
		    call send_byte(3)
		  }
		  case 3 {
		    loop_forever {
			trigger := 1
			nop 5
			call i2c_start()
			call i2c_send_byte(0xc0)
			nop 50
			call i2c_send_byte(0)
			call i2c_stop()
			nop 50
			call i2c_start()
			call i2c_send_byte(0xc1)
			nop 50
			temporary := i2c_get_byte()
			call i2c_stop()
			portc := temporary
			trigger := 0
			call delay()
		    }
		  }
		  case 4, 5, 6, 7 {
		    # (Command == (0000 01xx):
		  }
		}
	      }
	      case 1 {
		# (Command = 0000 1xxx):
	      }
	      case 2 {
		# (Command = 0001 0xxx):
	      }
	      case 3 {
		# (Command = 0001 1xxx):
	      }
	      case 4, 5, 6, 7 {
		# (Command = 001x xxxx):
	      }
	    }
	  }
	  case 1 {
	    # (Command = 01xx xxxx):
	    # Do nothing:
	  }
	  case 2 {
	    # (Command = 10xx xxxx):
	    # Do nothing:
	  }
	  case 3 {
	    # (Command = 11xx xxxx):
	    switch ((command >> 3) & 7) {
	      case 0, 1, 2, 3, 4 {
		# (Command = 110x xxxx or 1110 0xxx):
		# Do nothing:
	      }
	      case 5 {
		# (Command = 1110 1xxx):
		if (command = 0xef) {
		    # Read Interrupt Bits (Command = 1110 1111):
		    temporary := 0
		    if (interrupt_pending) {
			temporary@0 := 1
		    }
		    if (interrupt_enable) {
			temporary@1 := 1
		    }
		    call send_byte(temporary)
		}
	      }
	      case 6 {
		# (Command = 1111 0xxx):
		# Switching between register banks generates bulky code;
		# Keep code generation in bank 0 by assigning command to
		# temporary:
		temporary := command
		switch (temporary & 7) {
		  case 0, 1, 2, 3 {
		    # Set Interrupt Bits (Command = 1111 00ep):
		    interrupt_enable := temporary@1
		    interrupt_pending := temporary@0
		  }
		  case 4, 5 {
		    # Set Interrupt Pending (Command = 1111 010p):
		    interrupt_pending := temporary@0
		  }
		  case 6, 7 {
		    # Set Interrupt Enable (Command = 1111 011e):
		    interrupt_enable := temporary@0
		  }
		}
	      }
	      case 7 {
		switch (command & 7) {
 		  case 0 {
		    # Clock Decrement (Command = 1111 1000):
		    osccal := osccal - osccal_lsb
		  }
		  case 1 {
		    # Clock Increment (Command = 1111 1001):
		    osccal := osccal + osccal_lsb
		  }
 		  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):
		    call send_byte(id[index])
		    index := index + 1
		    if (index >= id.size) {
			index := 0
		    }
		  }
		  case 5 {
		    # ID Reset (Command = 1111 1101):
		    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
		    }
		  }
		}
	      }
	    }
	  }
	}
    }
}