isrs.S

/*
 * ----------------------------------------------------------------------------
 * "THE BEER-WARE LICENSE" (Revision 42):
 * Joerg Wunsch wrote this file.  As long as you retain this notice you
 * can do whatever you want with this stuff. If we meet some day, and you think
 * this stuff is worth it, you can buy me a beer in return.        Joerg Wunsch
 * ----------------------------------------------------------------------------
 *
 * Demo combining C and assembly source files.
 *
 * $Id$
 */
/*
 * This file contains the interrupt service routine implementations
 * when compiling the project for the ATtiny13 target.
 */

#include <avr/io.h>

#include "project.h"

#if defined(__AVR_ATtiny13__)

/*
 * Timer 0 hit TOP (0xff), i.e. it turns from up-counting
 * into down-counting direction.
 */
.global TIM0_COMPA_vect
TIM0_COMPA_vect:
    in  sreg_save, _SFR_IO_ADDR(SREG)
    inc counter_hi
    clr flags
    out _SFR_IO_ADDR(SREG), sreg_save
    reti

/*
 * Timer 0 hit BOTTOM (0x00), i.e. it turns from down-counting
 * into up-counting direction.
 */
.global TIM0_OVF_vect
TIM0_OVF_vect:
    in  sreg_save, _SFR_IO_ADDR(SREG)
    inc counter_hi
    ser flags
    out _SFR_IO_ADDR(SREG), sreg_save
    reti

;;; one 16-bit word to store our rising edge's timestamp
.lcomm  starttime.0, 2

.extern pwm_incoming
.extern intbits

.global PCINT0_vect
PCINT0_vect:
    in  sreg_save, _SFR_IO_ADDR(SREG)

    ;; save our working registers
    push    r18
    push    r19
    push    r20
    push    r21

    ;; Now that we are ready to fetch the current
    ;; value of TCNT0, allow interrupts for a
    ;; moment.  As the effect of the SEI will be
    ;; deferred by one instruction, any possible
    ;; rollover of TCNT0 (hitting BOTTOM when
    ;; counting down, or MAX when counting up) will
    ;; allow the above ISRs to trigger right here,
    ;; and update their status, so our combined
    ;; 16-bit time from [counter_hi, TCNT0] will
    ;; be correct.
    sei
    in  r20, _SFR_IO_ADDR(TCNT0)
    cli
    ;; Now, make our working copy of the status,
    ;; so we can re-enable interrupts again.
    mov r21, counter_hi
    mov r19, flags
    sei

    ;; what direction were we counting?
    sbrs    r19, 0
    ;; we are down-counting, invert TCNT0
    com r20
    ;; at this point, r21:20 has our current
    ;; 16-bit time

    ;; now, look which of the edges triggered
    ;; our pin-change interrupt
    sbis    _SFR_IO_ADDR(PINB), 4
    rjmp    10f
    ;; rising edge detected, just record starttime
    sts (starttime.0) + 1, r21
    sts starttime.0, r20
    rjmp    99f     ; we are done here

    ;; Falling edge: compute pulse width, store it
    ;; into pwm_incoming, disable pin-change
    ;; interrupt until the upper layers had a chance
    ;; to fetch the result.

10: in  r18, _SFR_IO_ADDR(GIMSK)
    andi    r18, ~(1 << PCIE)
    out _SFR_IO_ADDR(GIMSK), r18

    ;; pwm_incoming = current_time - starttime
    lds r19, (starttime.0) + 1
    lds r18, starttime.0
    sub r20, r18
    sbc r21, r19
    sts (pwm_incoming) + 1, r21
    sts pwm_incoming, r20

    ;; signal upper layer
    lds r18, intbits
    ori r18, 1
    sts intbits, r18
99:
    pop r21
    pop r20
    pop r19
    pop r18

    out _SFR_IO_ADDR(SREG), sreg_save
    reti
#endif  /* ATtiny13 */