--
--    Copyright (c) 2005 Riad S. Wahby <rsw@jfet.org>
--
--    This file is part of the Weston voltmeter clock code.
--
--    The Weston voltmeter clock code is free software; you can redistribute it and/or modify
--    it under the terms of the GNU General Public License as published by
--    the Free Software Foundation; either version 2 of the License, or
--    (at your option) any later version.
--
--    Foobar 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 General Public License for more details.
--
--    You should have received a copy of the GNU General Public License
--    along with Foobar; if not, write to the Free Software
--    Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
--

procedure intrh is
    -- this is the interrupt handler
    pragma interrupt            

    assembler
        local dofwd
        local doffwd
        local docounter
        local setpwm
        local setrealpwm
        local theend
        
        bcf intcon_gie          -- disable interrupts

        bcf status_rp1          -- in bank 0
        bcf status_rp0          -- ...

      -- see what kind of interrupt we got
        btfss intcon_rbif       -- if it's not a change on RB4-7
        goto docounter          -- then it's a counter interrupt

    -- handle port b
        btfsc pin_b4            -- if FWD
        goto dofwd      
        btfsc pin_b5            -- else if not FFWD
        goto doffwd
      -- back to normal
        movlw 0xC4              -- increment on every 60th input
        movwf clkset            -- 
        movlw 1                 -- increment seconds by 1
        movwf sincr             -- 
        goto theend
    dofwd:        
        movlw 0xFF              -- increment on every input
        movwf clkset            -- 
        movlw 1                 -- increment seconds by 1
        movwf sincr             -- 
        goto theend
    doffwd:
        movlw 0xFF              -- increment on every input
        movwf clkset            -- 
        movlw 60                -- increment seconds by 60
        movwf sincr             -- 
        goto theend

    docounter:                  -- handle a counter interrupt
        movf clkset,w           -- read in the initial counter value
        movwf tmr0              -- setup the next timing cycle
        movf sincr,w            -- read in the increment
        addwf seclo,f           -- add the increment to the seconds counter
        btfsc status_c          -- if there was a carry
        incf sechi,f            -- increment the high byte

        movf sechi,w            -- load the high byte
        xorlw 0xA8              -- are we over 12 hours?
        btfss status_z          -- if not
        goto setpwm             -- just keep going
        movlw 0xBF              -- seconds for the low byte
        subwf seclo,w           -- subtract BF from seconds
        btfss status_c          -- if seclo < BF
        goto setpwm             -- just keep going
        clrf sechi              -- else high byte is zero
        movwf seclo             -- low byte is overflow

    setpwm:
        movf port_b,w           -- read in port_b
        xorlw 0b_0000_0100      -- flip pin_b2
        movwf port_b            -- write it into port_b
        btfss pin_b0            -- unless in calibration mode
        goto setrealpwm         -- put in the real data
        movlw 0XA8              -- otherwise put in calib data
        movwf ccpr1l            -- high 8 bits
        bsf cp1x               -- 2nd lsb
        bcf cp1y               -- lsb
        goto theend                -- and we're done        

    setrealpwm:
        movf sechi,w            -- load the high bits of the duty cycle
        movwf ccpr1l            -- put them in the duty cycle register
        bcf cp1x               -- clear p1x
        btfsc seclox            -- but if we should set it
        bsf cp1x               -- do so
        bcf cp1y               -- clear p1y
        btfsc secloy            -- but if we should set it
        bsf cp1y               -- do so

    theend:
        bcf intcon_t0if         -- clear t0if
        bsf intcon_t0ie         -- enable timer interrupt
        bcf intcon_rbif         -- clear rbif
        bsf intcon_rbie         -- enable rb4:7 interrupt
        -- intcon_gie is set upon RETFIE
    end assembler
end procedure