Sound working at very low cpu frequencies

arduino/SN76489-test/SN76489-test.ino

@@ -16,7 +16,7 @@ void setup() {
   pinMode(WE, OUTPUT);
   digitalWrite(WE, HIGH);
 
-  /*  Init device (silence all channels)  
+  /*  Init device (silence all channels)
    *  Bits meaning:
    *  1 R0 R1 R2 A0 A1 A2 A3
    *    Bit0 is 1
@@ -32,7 +32,7 @@ void setup() {
 
   // Channel 1 to max volume
   SendByte(B10010000);
-  
+
   /*  Play note on channel 1
    *  Requires sending 2 bytes.
    *  Bits meaning:
@@ -50,7 +50,7 @@ void setup() {
    SendByte(B10000000); SendByte(B00001000);
    delay(500);
 
-   SendByte(B10011111);    // Sil ch 1 
+   SendByte(B10011111);    // Sil ch 1
 
    delay(1000);
 
@@ -65,7 +65,7 @@ void setup() {
    SendByte(B11000000); SendByte(B00001000);  // Note on ch3
    delay(500);
 
-   SendByte(B10011111);    // Sil ch 1 
+   SendByte(B10011111);    // Sil ch 1
    SendByte(B10111111);    // Sil ch 2
    SendByte(B11011111);    // Sil ch 3
 
@@ -73,13 +73,10 @@ void setup() {
    /*
     * Play noise on channel 4
     */
-  
-  
+
 }
 
-void loop() {
-  
-}
+void loop() {}
 
 void SendByte(byte b) {
   digitalWrite(DATA_BUS[0], (b&1)?HIGH:LOW);

assembly/bios/drivers/sn76489.asm

@@ -0,0 +1,50 @@
+; TI SN76489 sound chip display driver
+; @author Daniele Verducci
+;
+; USAGE:
+; call Snd_init                     <-- inits sound (and silences default tone)
+; call Snd_beep                     <-- system beep
+
+; Sound card is on port 0
+SND_DATA_REG: EQU IO_0
+
+; Init device (silence all channels)
+; Bits meaning:
+; 1 R0 R1 R2 A0 A1 A2 A3
+;   Bit0 is 1
+;   Bit1,2,3 select the channel: 001, 011, 101, 111(noise)
+;   Bit4,5,6,7 selecy the attenuation (0000=full volume, 1111=silent)
+Snd_init:
+    ; silence ch1
+    ld a,%11111001
+    ;ld a,%10011111
+    out (SND_DATA_REG),a
+    ; silence ch2
+     ld a,%11111101
+    ;ld a,%10111111
+    out (SND_DATA_REG),a
+    ; silence ch3
+     ld a,%11111011
+    ;ld a,%11011111
+    out (SND_DATA_REG),a
+    ; silence noise ch
+    ld a,%11111111
+    out (SND_DATA_REG),a
+    ret
+
+Snd_beep:
+    ; ch1 max volume
+    ld a,%10010000
+    out (SND_DATA_REG),a
+    ; play beep freq
+    ld a,%10000000
+    out (SND_DATA_REG),a
+    ld a,%00001000
+    out (SND_DATA_REG),a
+    ; wait 1 sec
+    ld bc, 10
+    call Time_delay55
+    ; silence ch1
+    ld a,%10011111
+    out (SND_DATA_REG),a
+    ret

assembly/bios/libs/time.asm

@@ -0,0 +1,19 @@
+; Time library
+; @author Daniele Verducci
+
+; Duration (change these values based on CPU frequency)
+TIME_DUR_SECOND: EQU 255
+
+; Wait bc * 55 states
+; Use 1 iteration as delay between I/O bus writes
+; @param bc The number of iterations. Each iteration is 55 states long.
+Time_delay55:
+    bit     0,a    ; 8
+    bit     0,a    ; 8
+    bit     0,a    ; 8
+    and     a,255  ; 7
+    dec     bc      ; 6
+    ld      a,c     ; 4
+    or      a,b     ; 4
+    jp      nz,Time_delay55   ; 10, total = 55 states/iteration
+    ret

assembly/bios/main.asm

@@ -42,38 +42,46 @@ IO_7: EQU 0xE0
 
 ;include 'drivers/hd44780.asm'
 ;include 'drivers/keyboard.asm'
-include 'drivers/arduino_terminal.asm'
-include 'monitor.asm'
+;include 'drivers/arduino_terminal.asm'
+include 'drivers/sn76489.asm'
+;include 'monitor.asm'
+include 'libs/time.asm'
+
 
 ; SYSTEM CALLS
 ; User I/O
 
-; Prints string
-; @param BC Pointer to a null-terminated string first character
-Print:
-    call Term_print
-    ret
+; ; Prints string
+; ; @param BC Pointer to a null-terminated string first character
+; Print:
+;     call Term_print
+;     ret
 
-; Writes a single character
-; @param A Value of character to print
-Printc:
-    call Term_printc
-    ret
+; ; Writes a single character
+; ; @param A Value of character to print
+; Printc:
+;     call Term_printc
+;     ret
 
-; Reads a single character
-; @return A The read character
-Readc:
-    call Term_readc
-    ret
+; ; Reads a single character
+; ; @return A The read character
+; Readc:
+;     call Term_readc
+;     ret
 
-; Reads a line
-; @return BC The pointer to a null-terminated read string
-Readline:
-    call Term_readline
-    ret
+; ; Reads a line
+; ; @return BC The pointer to a null-terminated read string
+; Readline:
+;     call Term_readline
+;     ret
 
 ; System initialization
 Sysinit:
     ; Start Monitor
-    call Monitor_main
+    ;call Monitor_main
+
+    call Snd_init
+    ld bc, 10
+    call Time_delay55
+    call Snd_beep
     halt