Rewrite of delay function

[uccvend-snackrom.git] / ROM2 / helpers.c

diff --git a/ROM2/helpers.c b/ROM2/helpers.c
index a35073c..b66f5ee 100644 (file)
--- a/ROM2/helpers.c
+++ b/ROM2/helpers.c
@@ -1,23 +1,32 @@
 #include "display_basic.h"
 #include "vend.h"
 
-#define DELAY_MAGIC 20 /* FIXME: number of loops for ~ 1 millisecond (< 256) */
 void delay(u16 ms) {
-       u8 i;
-       for (;ms;ms--) {
-               for (i=0;i<DELAY_MAGIC; i++)
-                       asm("nop\nnop\nnop\nnop\nnop\n");
-       }
-}
-
-void print_amount(u16 amt) {
-       /* take amt and show it on screen with a $ sign */
-       char str[10] = {' ', '$', ' ', ' ', ' ', ' ', ' ', ' ', ' ', ' '};
-       u8 pos;
-       for (pos = 7; amt; pos--, amt/=10) {
-               str[pos] = amt%10 + '0';
-       }
-       set_msg(str);
+       /* delay routine written in assembly so we know what we're really getting.
+        * each inner loop should take ~1 ms to execute.
+        * 15 cycles * (1/4.9152Mhz) * 327 = 0.997 ms + a little bit on the fringes.
+        *
+        * XXX - how do we know gcc isn't optimising this? it seems to optimise after
+        * parsing C -> asm, but before asm -> machine code.
+        */
+       asm volatile ("pshx\npsha\npshb\n"); /* save registers */
+       asm volatile ("ldx %0\n" :: "m" (ms));
+       asm volatile (
+               "loop:\n"
+               "       dex\n"                  /* 3 */
+               "       beq out\n"              /* 3 */
+               "       ldd #327\n"             /* 3 */
+               "inner_loop:\n" /* 15 cycles each */
+               "       cpd #0x0000\n"          /* 5 */
+               "       beq inner_loop_end\n"   /* 3 */
+               "       subd #0x0001\n"         /* 4 */
+               "       bra inner_loop\n"       /* 3 */
+               "inner_loop_end:\n"
+               "       bra loop\n"             /* 3 */
+               "out:\n"
+               "       pulb\n"
+               "       pula\n"
+               "       pulx\n");
 }
 
 void my_strncpy(char* dst, char* src, u8 max_size) {