tweaks cx16 sample streaming example, also added a new one

compiler/res/prog8lib/cx16/syslib.p8

@@ -1195,6 +1195,7 @@ asmsub set_sprcol_irq_handler(uword address @AY) clobbers(A) {
 asmsub set_aflow_irq_handler(uword address @AY) clobbers(A) {
     ; Sets the AFLOW irq handler to use with enable_irq_handlers().  Also enables AFLOW irqs.
     ; NOTE: unless a proper irq handler is already running, you should enclose this call in set_irqd() / clear_irqd() to avoid system crashes.
+    ; NOTE: the handler itself must fill the audio fifo buffer to at least 25% full again (1 KB) or the aflow irq will keep triggering!
     %asm {{
         php
         sei

compiler/test/TestCompilerOnExamples.kt

@@ -108,6 +108,7 @@ class TestCompilerOnExamplesCx16: FunSpec({
             "vtui/testvtui",
             "pcmaudio/play-adpcm",
             "pcmaudio/stream-wav",
+            "pcmaudio/stream-pcm-simple",
             "pcmaudio/vumeter",
             "sprites/dragon",
             "sprites/dragons",

docs/source/targetsystem.rst

@@ -224,6 +224,8 @@ Here they are, all available in ``cx16``:
 
 ``set_aflow_irq_handler (uword address)``
     Sets the audio buffer underrun interrupt handler routine.  Also enables AFLOW interrupts.
+    Note: the handler must fill the Vera's audio fifo buffer by itself with at least 25% worth of data (1 kb)
+    otherwise the aflow irq keeps triggering.
 
 ``disable_irq_handlers ()``
     Hand control back to the system default IRQ handler.

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

@@ -0,0 +1,124 @@
+; 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
+; 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.
+;
+; The IRQ handlers are installed using Prog8's support routines for irq handlers.
+; 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.init()
+            interrupts.setup()
+            music.start()
+        } else {
+            txt.print("\nio error")
+        }
+
+        repeat {
+            interrupts.wait()
+            if interrupts.aflow {
+                ; read the next 1024 bytes of audio data into the buffer
+                txt.chrout('.')
+                if diskio.f_read(interrupts.audio_buffer, 1024) != 1024
+                    break
+                interrupts.aflow = false
+            }
+        }
+    }
+}
+
+
+interrupts {
+    bool aflow
+    uword audio_buffer = memory("audiobuffer", 1024, 0)
+
+    sub setup() {
+        aflow = false
+        sys.memset(audio_buffer, 1024, 0)
+        cx16.enable_irq_handlers(true)
+        cx16.set_aflow_irq_handler(&aflow_handler)
+        ; no other irqs in this example.
+    }
+
+    asmsub wait() {
+        %asm {{
+            wai
+        }}
+    }
+
+    sub aflow_handler() -> bool {
+        ; 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
+        }}
+        aflow = true        ; signal main program to read the next block of audio data: it is unsafe to to I/O in a irq handler!
+        return false
+    }
+}
+
+music {
+    uword vera_rate_hz
+    ubyte vera_rate
+
+    sub init() {
+        cx16.VERA_AUDIO_RATE = 0            ; halt playback
+        cx16.VERA_AUDIO_CTRL = %10111011    ; stereo 16 bit, volume 11
+    }
+
+    sub start() {
+        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
+    }
+}

examples/cx16/pcmaudio/stream-wav.p8

@@ -128,10 +128,6 @@ main {
 
             repeat {
                 interrupts.wait()
-                if interrupts.vsync {
-                    interrupts.vsync=false
-                    ; ...do something triggered by vsync irq...
-                }
                 if interrupts.aflow {
                     interrupts.aflow=false
                     if not music.load_next_block(block_size)
@@ -158,13 +154,12 @@ interrupts {
 
     sub set_handler() {
         sys.set_irqd()
-        cx16.CINV = &handler         ; handles both AFLOW and VSYNC
+        cx16.CINV = &handler         ; handler for AFLOW
-        cx16.VERA_IEN = %00001001    ; enable AFLOW + VSYNC
+        cx16.VERA_IEN = %00001000    ; enable AFLOW only
         sys.clear_irqd()
     }
 
     bool aflow
-    bool vsync
 
     asmsub wait() {
         %asm {{
@@ -173,6 +168,8 @@ interrupts {
     }
 
     sub handler() {
+        ; we only handle aflow in this example.
+
         if cx16.VERA_ISR & %00001000 !=0 {
             ; Filling the fifo is the only way to clear the Aflow irq.
             ; So we do this here, otherwise the aflow irq will keep triggering.
@@ -183,10 +180,6 @@ interrupts {
             cx16.restore_virtual_registers()
             aflow = true
         }
-        if cx16.VERA_ISR & %00000001 !=0 {
-            cx16.VERA_ISR = %00000001
-            vsync = true
-        }
 
         %asm {{
             ply
@@ -233,23 +226,30 @@ music {
     }
 
     asmsub uncompressed_block_8() {
-        ; optimized loop to put 1024 bytes of data into the fifo as fast as possible
+        ; copy 1024 bytes of audio data from the buffer into vera's fifo, quickly!
-        ; converting unsigned wav 8 bit samples to signed 8 bit on the fly
+        ; converting unsigned wav 8 bit samples to signed 8 bit on the fly.
         %asm {{
             lda  p8v_buffer
-            sta  cx16.r0L
+            sta  _loop+1
+            sta  _lp2+1
             lda  p8v_buffer+1
-            sta  cx16.r0H
+            sta  _loop+2
+            sta  _lp2+2
             ldx  #4
--           ldy  #0
+            ldy  #0
--           lda  (cx16.r0),y
+_loop       lda  $ffff,y
-            eor  #$80       ; convert to signed 8-bit
+            eor  #$80       ; convert to signed
             sta  cx16.VERA_AUDIO_DATA
             iny
-            bne  -
+_lp2        lda  $ffff,y
-            inc  cx16.r0H
+            eor  #$80       ; convert to signed
+            sta  cx16.VERA_AUDIO_DATA
+            iny
+            bne  _loop
+            inc  _loop+2
+            inc  _lp2+2
             dex
-            bne  --
+            bne  _loop
             rts
         }}
 
@@ -264,22 +264,27 @@ music {
     }
 
     asmsub uncompressed_block_16() {
-        ; optimized loop to put 1024 bytes of data into the fifo as fast as possible
+        ; copy 1024 bytes of audio data from the buffer into vera's fifo, quickly!
         %asm {{
             lda  p8v_buffer
-            sta  cx16.r0L
+            sta  _loop+1
+            sta  _lp2+1
             lda  p8v_buffer+1
-            sta  cx16.r0H
+            sta  _loop+2
+            sta  _lp2+2
             ldx  #4
--           ldy  #0
+            ldy  #0
--           lda  (cx16.r0),y
+_loop       lda  $ffff,y
             sta  cx16.VERA_AUDIO_DATA
             iny
-            bne  -
+_lp2        lda  $ffff,y
-            inc  cx16.r0H
+            sta  cx16.VERA_AUDIO_DATA
+            iny
+            bne  _loop
+            inc  _loop+2
+            inc  _lp2+2
             dex
-            bne  --
+            bne  _loop
-            rts
         }}
 ; original prog8 code:
 ;        uword @requirezp ptr = main.start.buffer