optimize clobbers

Author: nerdralph

src/ArduinoShrink.h

@@ -11,7 +11,7 @@ inline void delay(uint32_t msec)
         "%~call %x1\n" 
         : "+r"(ms)
         : "i"(delay_impl)
-        : "r19", "r20", "r21"           // clobbers
+        : "r20", "r21"           // clobbers
     );
 }
 

src/delay.S

@@ -6,23 +6,23 @@
 #include <avr/io.h>
 #include "macros.inc"
 
-#define remain  r19
-#define start   r20
+#define start   r0
+#define remain  r20
 #define current r21
 ; delay for r26:r24 (u24) ms
 GLABEL delay_impl
     in  start, TCNT0
     ldi remain, lo8(T0CNT_PER_MS)
-wait1ms:                                ; check TCNT0 until 1ms has passed
+_wait1ms:                                ; check TCNT0 until 1ms has passed
     in  current, TCNT0
     sub current, start
     add start, current                  ; advance start
     sub remain, current
-    brcc wait1ms
+    brcc _wait1ms
     subi remain, lo8(-(T0CNT_PER_MS))   ; add 1ms
-decms:                                  ; decrement ms argument
+    ; decrement ms argument
     sbiw r24, 1
     sbci r26, 0
-    brne wait1ms
+    brne _wait1ms
     ret