cx16: added a polling pcm streaming example

compiler/test/TestCompilerOnExamples.kt

@@ -108,7 +108,8 @@ class TestCompilerOnExamplesCx16: FunSpec({
             "vtui/testvtui",
             "pcmaudio/play-adpcm",
             "pcmaudio/stream-wav",
-            "pcmaudio/stream-pcm-simple",
+            "pcmaudio/stream-simple-aflow",
+            "pcmaudio/stream-simple-poll",
             "pcmaudio/vumeter",
             "sprites/dragon",
             "sprites/dragons",

docs/source/todo.rst

@@ -3,6 +3,16 @@ TODO
 
 See open issues on github.
 
+Asm peephole optimizer: while cx16.VERA_AUDIO_CTRL & %01000000 == 0 { } compiles into the following. Replace the bne+bra into a beq. Similar for !=0 I guess?
+    p8l_label_5_whileloop
+        lda  cx16.VERA_AUDIO_CTRL
+        and  #$40
+        bne  p8l_label_6_afterwhile
+        bra  p8l_label_5_whileloop
+    p8l_label_6_afterwhile
+
+Codegen: use BIT instruction for memory location bit 7 and 6 tests (use N and V flags)
+
 Re-generate the skeletons doc files.
 
 Improve register load order in subroutine call args assignments:

examples/cx16/pcmaudio/stream-simple-aflow.p8

@@ -1,9 +1,11 @@
 ; This program can stream a simple uncompressed PCM file from the sdcard.
-; Currently it has been set up to play a 16 bit stereo PCM file,
-; and it plays it in the given sample frequency typed in by the user.
 ;
-; It uses a AFLOW irq handler to refill the vera's PCM fifo buffer,
-; and sets a flag that signals the main program to load the next block of
+; It is hardwired to play a 16 bit stereo PCM file,
+; but you can type in the sample rate you want to play it in.
+;
+; It uses a AFLOW irq handler to refill the vera's PCM fifo buffer.
+;
+; The irq handler sets a flag that signals the main program to load the next block of
 ; data from disk.  It is problematic to call kernal I/O routines inside an irq handler,
 ; otherwise the aflow handler itself could have loaded the pcm data straight into
 ; the vera's fifo buffer.  But this could lead to race conditions so we need explicit buffering.

examples/cx16/pcmaudio/stream-simple-poll.p8

@@ -0,0 +1,106 @@
+; This program can stream a simple uncompressed PCM file from the sdcard.
+;
+; It is hardwired to play a 16 bit stereo PCM file,
+; but you can type in the sample rate you want to play it in.
+;
+; It uses simple polling on the AFLOW flag rather than actually using a IRQ hander,
+; to see when to refill the FIFO buffer.
+;
+; The sample data is simply read using diskio.f_read() routine, but that uses MACPTR internally for fast loads.
+
+
+%import diskio
+%import textio
+%option no_sysinit
+
+main {
+
+    sub start() {
+        str MUSIC_FILENAME = "?"*32
+        txt.print("what sample rate (hz) do you want to play at: ")
+        void txt.input_chars(MUSIC_FILENAME)
+        music.vera_rate_hz = conv.str2uword(MUSIC_FILENAME)
+        if music.vera_rate_hz==0
+            music.vera_rate_hz=44100
+        music.calculate_vera_rate(music.vera_rate_hz)
+
+        txt.print("\nname of raw .pcm file to play on drive 8: ")
+        while 0==txt.input_chars(MUSIC_FILENAME) {
+            ; until user types a name...
+        }
+
+        if diskio.f_open(MUSIC_FILENAME) {
+            cx16.rombank(0)
+            void diskio.fastmode(1)
+            music.start()
+            while music.stream() {
+                txt.chrout('.')
+            }
+        } else {
+            txt.print("\nio error")
+        }
+    }
+}
+
+
+music {
+    uword audio_buffer = memory("audiobuffer", 1024, 0)
+
+    uword vera_rate_hz
+    ubyte vera_rate
+
+    sub start() {
+        cx16.VERA_AUDIO_RATE = 0            ; halt playback
+        cx16.VERA_AUDIO_CTRL = %10111011    ; stereo 16 bit, volume 11
+        sys.memset(audio_buffer, 1024, 0)
+        cx16.VERA_AUDIO_RATE = vera_rate    ; start playback
+    }
+
+    sub calculate_vera_rate(uword sample_rate) {
+        const uword vera_freq_factor = 25_000_000 / 65536
+        vera_rate = (sample_rate / vera_freq_factor) as ubyte + 1
+        vera_rate_hz = vera_rate * vera_freq_factor
+    }
+
+    sub stream() -> bool {
+        while cx16.VERA_ISR & %00001000 == 0 {
+            ; poll until AFLOW is raised ("fifo is less than 25% full, feed me more data soon!")
+        }
+
+        ; Reading directly from disk into the audio fifo is possible, but can result in hick ups.:
+        ; diskio.reset_read_channel()
+        ; void, cx16.r14 = cx16.MACPTR(0, &cx16.VERA_AUDIO_DATA, true)
+        ; void, cx16.r15 = cx16.MACPTR(0, &cx16.VERA_AUDIO_DATA, true)
+        ; return cx16.r14+cx16.r15 == 1024
+
+        ; so instead: copy current buffer to Vera audio FIFO and immediately read the next 1 KB block from disk into the buffer.
+        fill_fifo()
+        return diskio.f_read(audio_buffer, 1024) == 1024
+    }
+
+    asmsub fill_fifo() {
+        ; copy 1024 bytes of audio data from the buffer into vera's fifo, quickly!
+        %asm {{
+            lda  p8v_audio_buffer
+            sta  _loop+1
+            sta  _lp2+1
+            lda  p8v_audio_buffer+1
+            sta  _loop+2
+            sta  _lp2+2
+            ldx  #4
+            ldy  #0
+_loop       lda  $ffff,y
+            sta  cx16.VERA_AUDIO_DATA
+            iny
+_lp2        lda  $ffff,y
+            sta  cx16.VERA_AUDIO_DATA
+            iny
+            bne  _loop
+            inc  _loop+2
+            inc  _lp2+2
+            dex
+            bne  _loop
+            rts
+        }}
+    }
+}