Jul 7, 2020 · Jul 7, 2020
diff --git a/cores/arduino/wiring_pulse.S b/cores/arduino/wiring_pulse.S
  wiring_pulse.s - pulseInASM() function in different flavours
  Part of Arduino - http://www.arduino.cc/

  Copyright (c) 2014 Martino Facchin
  Copyright (c) 2014 Martino Facchin, 2020 Spence Konde

  This library is free software; you can redistribute it and/or
  modify it under the terms of the GNU Lesser General Public
 * }
 *
 * some compiler outputs were removed but the rest of the code is untouched
 *
 * Spence feb 2020: not untouched anymore! The first two loops ran in 11 cycles instead
 * of 16, so if no pulse was detected, the timeout would be reached when
 * 11/16ths of the requested timeout had elapsed. This was fixed by the addition
 * of 2 rjmps to the next line (a 2 cycle nop that uses only 1 word) and 1 nop
 * to each of these loops before they decrement maxloops.
 * Additionally, removed duplication of return sequence to save 12b flash
 * which is conveniently exactly how much the other fix cost.
 */

 #include <avr/io.h>
 .L4:
 /*         if (--maxloops == 0) */
 .LM2:
    rjmp .LM2A ; waste an extra 5 cycles
 .LM2A:
    rjmp .LM2B ;
 .LM2B:
    nop ;
    subi r16,1   ;  maxloops,  ;  17  addsi3/2  [length = 4]
    sbc r17, r1   ;  maxloops
    sbc r18, r1   ;  maxloops
 ***         if (--maxloops == 0)
 */
 .LM4:
    rjmp .LM4A ; waste an extra 5 cycles
 .LM4A:
    rjmp .LM4B ;
 .LM4B:
    nop ;
    subi r16,1   ;  maxloops,  ;  31  addsi3/2  [length = 4]
    sbc r17, r1   ;  maxloops
    sbc r18, r1   ;  maxloops
    mov r23,r13  ;  D.1553, width  ;  109 movqi_insn/1  [length = 1]
    mov r24,r14  ;  D.1553, width  ;  110 movqi_insn/1  [length = 1]
    mov r25,r15  ;  D.1553, width  ;  111 movqi_insn/1  [length = 1]
    rjmp .LM11 ;
 /* epilogue start */
 .LM9:
    pop r17  ;   ;  171 popqi [length = 1]
    pop r16  ;   ;  172 popqi [length = 1]
    pop r15  ;   ;  173 popqi [length = 1]
    pop r14  ;   ;  174 popqi [length = 1]
    pop r13  ;   ;  175 popqi [length = 1]
    pop r12  ;   ;  176 popqi [length = 1]
    ret  ;  177 return_from_epilogue  [length = 1]
 .L13:
 .LM10:
    ldi r22,0  ;  D.1553   ;  120 movqi_insn/1  [length = 1]
Original file line number	Diff line number	Diff line change
Expand Up		@@ -2,7 +2,7 @@
		wiring_pulse.s - pulseInASM() function in different flavours
		Part of Arduino - http://www.arduino.cc/

		Copyright (c) 2014 Martino Facchin
		Copyright (c) 2014 Martino Facchin, 2020 Spence Konde

		This library is free software; you can redistribute it and/or
		modify it under the terms of the GNU Lesser General Public
Expand DownExpand Up		@@ -47,6 +47,14 @@
		* }
		*
		* some compiler outputs were removed but the rest of the code is untouched
		*
		* Spence feb 2020: not untouched anymore! The first two loops ran in 11 cycles instead
		* of 16, so if no pulse was detected, the timeout would be reached when
		* 11/16ths of the requested timeout had elapsed. This was fixed by the addition
		* of 2 rjmps to the next line (a 2 cycle nop that uses only 1 word) and 1 nop
		* to each of these loops before they decrement maxloops.
		* Additionally, removed duplication of return sequence to save 12b flash
		* which is conveniently exactly how much the other fix cost.
		*/

		#include <avr/io.h>
Expand DownExpand Up		@@ -80,6 +88,11 @@ countPulseASM:
		.L4:
		/* if (--maxloops == 0) */
		.LM2:
		rjmp .LM2A ; waste an extra 5 cycles
		.LM2A:
		rjmp .LM2B ;
		.LM2B:
		nop ;
		subi r16,1 ; maxloops, ; 17 addsi3/2 [length = 4]
		sbc r17, r1 ; maxloops
		sbc r18, r1 ; maxloops
Expand All		@@ -101,6 +114,11 @@ countPulseASM:
		*** if (--maxloops == 0)
		*/
		.LM4:
		rjmp .LM4A ; waste an extra 5 cycles
		.LM4A:
		rjmp .LM4B ;
		.LM4B:
		nop ;
		subi r16,1 ; maxloops, ; 31 addsi3/2 [length = 4]
		sbc r17, r1 ; maxloops
		sbc r18, r1 ; maxloops
Expand DownExpand Up		@@ -152,15 +170,8 @@ countPulseASM:
		mov r23,r13 ; D.1553, width ; 109 movqi_insn/1 [length = 1]
		mov r24,r14 ; D.1553, width ; 110 movqi_insn/1 [length = 1]
		mov r25,r15 ; D.1553, width ; 111 movqi_insn/1 [length = 1]
		rjmp .LM11 ;
		/* epilogue start */
		.LM9:
		pop r17 ; ; 171 popqi [length = 1]
		pop r16 ; ; 172 popqi [length = 1]
		pop r15 ; ; 173 popqi [length = 1]
		pop r14 ; ; 174 popqi [length = 1]
		pop r13 ; ; 175 popqi [length = 1]
		pop r12 ; ; 176 popqi [length = 1]
		ret ; 177 return_from_epilogue [length = 1]
		.L13:
		.LM10:
		ldi r22,0 ; D.1553 ; 120 movqi_insn/1 [length = 1]
Expand Down