sound chips added to pld file and added sn76489 test

bios.asm

@@ -145,6 +145,7 @@ init:
     ei
 
     call        tape_init
+    call        psg_silence
 
     ; Print header message
     ld          hl,msg_header
@@ -272,6 +273,13 @@ release_daisy_chain:
 ctc_uart_init:
     ; Reset CTC channels
     ld          a,003h
+    ; A channel may still be waiting for a time constant after a warm boot.
+    ; In that state the first byte is consumed as the constant, so send the
+    ; reset control word again to guarantee the unused channel is disabled.
+    out         (CTC_CHANNEL_0),a
+    out         (CTC_CHANNEL_1),a
+    out         (CTC_CHANNEL_2),a
+    out         (CTC_CHANNEL_3),a
     out         (CTC_CHANNEL_0),a
     out         (CTC_CHANNEL_1),a
     out         (CTC_CHANNEL_2),a
@@ -557,6 +565,20 @@ delay_ms:
     jp          nz,1$           ; 10T
     ret
 
+; -------------------------------------------------------
+; Silence all audio generators
+; -------------------------------------------------------
+psg_silence:
+    ld a,0x9f       ; mute tone 0
+    out (SN_PORT),a
+    ld a,0xbf       ; mute tone 1
+    out (SN_PORT),a
+    ld a,0xdf       ; mute tone 2
+    out (SN_PORT),a
+    ld a,0xff       ; mute noise
+    out (SN_PORT),a
+    ret
+
 ; -------------------------------------------------------
 ; Strings
 ; -------------------------------------------------------