[avr-libc-commit] [2348] Modified system_tick as advised by Wouter van Gulik...

[Mike Rice]

Revision: 2348
          http://svn.sv.gnu.org/viewvc/?view=rev&root=avr-libc&revision=2348
Author:   swfltek
Date:     2013-04-16 23:42:05 +0000 (Tue, 16 Apr 2013)
Log Message:
-----------
Modified system_tick as advised by Wouter van Gulik... 25% fewer cpu cycles and 
75% less stack usage.

Modified Paths:
--------------
    trunk/avr-libc/libc/time/system_tick.S

Modified: trunk/avr-libc/libc/time/system_tick.S
===================================================================
--- trunk/avr-libc/libc/time/system_tick.S      2013-04-14 16:55:04 UTC (rev 
2347)
+++ trunk/avr-libc/libc/time/system_tick.S      2013-04-16 23:42:05 UTC (rev 
2348)
@@ -29,7 +29,7 @@
 /* $Id$ */
 
 /*
-       This function increments __system time by one second. It is safe to 
call from a 'naked' ISR.
+    Impoved system_tick Credit to Wouter van Gulik.
 */
 
 #include <avr/common.h>
@@ -38,31 +38,23 @@
        .type   system_tick, @function
 system_tick:
     push r24
-       push r25
-       push r26
-       push r27
-       push r1
-       in r1,_SFR_IO_ADDR(SREG)
-       push r1
-       clr r1
+    in r24,_SFR_IO_ADDR(SREG)
+       push r24
        cli
-       lds r24,__system_time
-       lds r25,__system_time+1
-       lds r26,__system_time+2
-       lds r27,__system_time+3
-       adiw r24,1
-       adc r26,r1
-       adc r27,r1
-       sts __system_time,r24
-       sts __system_time+1,r25
-       sts __system_time+2,r26
-       sts __system_time+3,r27
-       pop r1
-       out _SFR_IO_ADDR(SREG),r1
-       pop r1
-       pop r27
-       pop r26
-       pop r25
-       pop r24
-       ret
+    lds r24,__system_time+0
+    subi r24, (-1)
+    sts __system_time+0,r24
+    lds r24,__system_time+1
+    sbci r24, (-1)
+    sts __system_time+1,r24
+    lds r24,__system_time+2
+    sbci r24, (-1)
+    sts __system_time+2,r24
+    lds r24,__system_time+3
+    sbci r24, (-1)
+    sts __system_time+3,r24
+    pop r24
+    out _SFR_IO_ADDR(SREG),r24
+    pop r24
+    ret
        .size   system_tick, .-system_tick