o audio

- added licence information for referenced source code
    - corrected type used for poly9bit

hardware/tia/audio/audio.go

@@ -30,7 +30,7 @@ type Audio struct {
 
 	poly4bit [15]uint8
 	poly5bit [31]uint8
-	poly9bit [511]uint8
+	poly9bit [511]uint16
 	div31    [31]uint8
 
 	// From the "Stella Programmer's Guide":
@@ -71,7 +71,7 @@ func NewAudio() *Audio {
 	// "Rather than have a table with 511 entries, I use a random number
 	// generator."
 	for i := 0; i < len(au.poly9bit); i++ {
-		au.poly9bit[i] = uint8(rand.Int() & 0x01)
+		au.poly9bit[i] = uint16(rand.Int() & 0x01)
 	}
 
 	// from TIASound.c:

hardware/tia/audio/channels.go

@@ -51,9 +51,6 @@ func (ch *channel) String() string {
 
 // tick should be called at a frequency of 30Khz. when the 10Khz clock is
 // required, the frequency clock is increased by a factor of three.
-//
-// the logic in this function is taken almost directly from the TIA_process()
-// function in Ron Fries' TIASound.c
 func (ch *channel) tick() {
 	// tick frequency clock
 	if ch.freqClk > 1 {
@@ -83,7 +80,7 @@ func (ch *channel) tick() {
 	if (ch.regControl&0x02 == 0x0) ||
 		((ch.regControl&0x01 == 0x0) && ch.au.div31[ch.poly5ct] != 0) ||
 		((ch.regControl&0x01 == 0x1) && ch.au.poly5bit[ch.poly5ct] != 0) ||
-		((ch.regControl&0x0f == 0xf) && ch.au.poly5bit[ch.poly5ct] == prevBit5) {
+		((ch.regControl&0x0f == 0xf) && ch.au.poly5bit[ch.poly5ct] != prevBit5) {
 
 		if ch.regControl&0x04 == 0x04 {
 			// use pure clock

hardware/tia/audio/doc.go

@@ -8,4 +8,10 @@
 // function in Frie's implementation meanwhile is called to fill a buffer. The
 // samepl buffer in this emulation must sit outside of the TIA emulation and
 // somwhere inside the television implementation.
+//
+// TIASound.c is published under the GNU Library GPL v2.0
+//
+// Some modifications were made to Fries' alogorithm in accordance to similar
+// modifications made to the TIASnd.cxx file of the Stella emulator v5.1.3.
+// Stella is published under the GNU GPL v2.0
 package audio