From 79ac4b750e2e75ae4a43f89efc87544be438dfec Mon Sep 17 00:00:00 2001
From: Brion Vibber <brion@pobox.com>
Date: Sun, 11 Dec 2022 13:09:14 -0800
Subject: [PATCH] alt audio

---
 atari-asm-xex.cfg |  1 +
 dither4.s         | 30 +++++++++++-------------------
 pack-wav.js       |  7 +++++--
 3 files changed, 17 insertions(+), 21 deletions(-)

diff --git a/atari-asm-xex.cfg b/atari-asm-xex.cfg
index e8888e9..5fc0c97 100644
--- a/atari-asm-xex.cfg
+++ b/atari-asm-xex.cfg
@@ -21,5 +21,6 @@ SEGMENTS {
     RODATA:   load = MAIN,    type = ro   optional = yes;
     DATA:     load = MAIN,    type = rw   optional = yes;
     BSS:      load = MAIN,    type = bss, optional = yes, define = yes;
+    AUDIO:    load = MAIN,    type = ro,  optional = yes, define = yes, align = 256;
     BUFFERS:  load = MAIN,    type = ro,  optional = yes, define = yes, align = 4096;
 }
diff --git a/dither4.s b/dither4.s
index 3a8c0f9..86eb46d 100644
--- a/dither4.s
+++ b/dither4.s
@@ -168,6 +168,7 @@ wait_loop:
 
     .macro audio_play_raw
         ;ldy VCOUNT ; set on entry
+        ldy #0             ; 2 cycles
         lda (sample_ptr),y ; 5/6 cyc
         sta AUDC1          ; 4 cyc
     .endmacro
@@ -187,22 +188,14 @@ wait_loop:
 
     .macro audio_inc
         ; Increment sample ptr
-        ; 18 cycles
-        clc             ; 2
-        lda sample_ptrl ; 3
-        adc #131        ; 2
-        sta sample_ptrl ; 3
-        lda sample_ptrh ; 3
-        adc #0          ; 2
-        sta sample_ptrh ; 3
-
-        ; 4 cycles
-        cmp #.hibyte(audio_samples_end) ; 2
-        bmi audio_cont                  ; 2
+        ; 7 cycles
+        inc sample_ptrl ; 5
+        bne audio_cont  ; 2
 
         ; 7 cycles, optional
-        lda sample_ptrl                 ; 3
-        cmp #.lobyte(audio_samples_end) ; 2
+        inc sample_ptrh                 ;5
+        lda sample_ptrh                 ; 3
+        cmp #.hibyte(audio_samples_end) ; 2
         bmi audio_cont                  ; 2
 
         ; 10 cycles, optional
@@ -221,21 +214,20 @@ wait_loop:
         sty scanline ; 3 cycles
         inner_scanline frame_offset, 0 ; 23-26 cycles before break, 12 cycles after
 
+        audio_play_raw ; 11-12 cycles
         ldy scanline   ; 3 cycles
-        audio_play_raw ; 9-10 cycles
         ;audio_play_lo
         inner_scanline frame_offset, 128 ; 23-26 cycles before break, 12 cycles after
+
+        audio_inc         ; 7-24 cycles
         ;audio_play_raw
         ;audio_play_hi ; too slow
 
-        ; save for audio lookup
+        ; save for later lookup
         ldy VCOUNT             ; 4 cycles
         cpy #0                 ; 2 cycles
         bne each_scanline_pair ; 2 cycles
 
-        ; only once when we hit scanline 0:
-        audio_inc         ; 22-39 cycles
-
         lda frame_counter ; 3 cycles
         eor #1            ; 2 cycles
         sta frame_counter ; 3 cycles
diff --git a/pack-wav.js b/pack-wav.js
index c879448..4a74a81 100644
--- a/pack-wav.js
+++ b/pack-wav.js
@@ -43,10 +43,13 @@ function pack(audio) {
 }
 
 function audio2assembly(audio) {
-    return `.data
+    return `
+.segment "AUDIO"
+
     .export audio_samples
     .export audio_samples_end
 
+.align 256
 audio_samples:
     ${byte2byte(pack(audio))}
 audio_samples_end:
@@ -58,7 +61,7 @@ audio_samples_end:
 function wav2assembly(buffer) {
     let wav = new WaveFile(buffer);
     let samples = wav.getSamples();
-    let n = samples.length - (samples.length % 131);
+    let n = samples.length - (samples.length % 256);
     return audio2assembly(samples.slice(0, n));
 }