partial: Account for frame drops

Define tracing variables when PARTIAL=1, which is only on a development
environment. This way we can detect whether we are dropping frames or
not.

Signed-off-by: Miquel Sabaté Solà <mikisabate@gmail.com>

1 files changed, 22 insertions, 1 deletions

diff --git a/src/vectors.s b/src/vectors.s
index 8928aaf..75de30a 100644
--- a/src/vectors.s
+++ b/src/vectors.s
@@ -3,6 +3,12 @@
 
 .segment "CODE"
 
+;; Debug utilities.
+.scope Debug
+    ;; Counter for frame drops.
+    zp_frame_drops = $90
+.endscope
+
 ;; Pretty standard reset function, nothing crazy.
 .proc reset
     ;; Disable interrupts and decimal mode.
@@ -29,6 +35,12 @@
     bit PPU::STATUS
     bpl @vblankwait1
 
+    ;; Initialize the counter for frame drops before any NMIs can come in.
+    .ifdef PARTIAL
+        lda #0
+        sta Debug::zp_frame_drops
+    .endif
+
     ;; Reset all sprites by simply moving the Y coordinate out of screen.
     lda #$EF
     ldx #0
@@ -60,7 +72,13 @@
 .proc nmi
     ;; Should we skip it?
     bit Globals::zp_flags
-    bpl @end
+
+    ;; If we are on a dev environment, account for any frame drops.
+    .ifdef PARTIAL
+        bpl @account_for_frame_drop
+    .else
+        bpl @end
+    .endif
 
     ;; Save registers.
     pha
@@ -131,6 +149,9 @@
 
 @end:
     rti
+@account_for_frame_drop:
+    inc Debug::zp_frame_drops
+    rti
 .endproc
 
 ;; Unused.