new version

check which registers are first used by MOV, which rely on being cleared

diff --git a/foo.c b/foo.c
index d708f3c50970642d7272f0b539e9cc66c2a31835..88dd7784facf2793847446cce456e91182f4c2c6 100644 (file)
--- a/foo.c
+++ b/foo.c
@@ -11,9 +11,9 @@ u8 i0;
 u8 i1;
 u8 i2;
 u8 i3;
-u8 t;
-u8 x;
-u8 _;
+u8 t;  //implicitly cleared by mov t,n
+u8 x;  //implicitly cleared by mov x,s
+u8 _;  //implicitly cleared by mov tmp,*
 #define Mh x //mod3 vars
 #define Ml t // -"-
 //http://homepage.divms.uiowa.edu/~jones/bcd/mod.shtml
@@ -66,14 +66,14 @@ void g(void) {
          ADC X_hi, zero
          LD  t, X         */
        t = (((i1&0x1f)<<8|i0)*t)>>8; //TODO
-       RET //TODO: CALL/RET is expensive; store next-instruction-position in Z register and RJMP, then JRMP back (maybe unnecessary, since timer might need stack anyways)
+       RET //TODO: replace CALL/RET with IJMP?
 };
 
 int main(void) {
-       u8 n;
-       u8 s;
-       u8 acc;
-       //TODO: clear all vars/registers
+       u8 n;  //implicitly cleared by mov n,i2
+       u8 s;  //implicitly cleared by mov s,i3
+       u8 acc;//implicitly cleared by mov acc,t
+       //TODO: clear i0, i1, i2, i3, zero registers
        for (;;) {
                MOV     (n, i2)
                LSL     (n)