From: Tobias Girstmair <tobi@isticktoit.net>
Date: Tue, 27 Apr 2021 08:15:07 +0000 (+0200)
Subject: increase PWM frequency to 64kHz
X-Git-Url: https://git.gir.st/Chiptunes-pms150c.git/commitdiff_plain/82fa1697cabbd9d3cea5efce931e109660490796

increase PWM frequency to 64kHz

audio is still borked, though
---

diff --git a/bsv.asm b/bsv.asm
index f31ee13..8a73ba5 100644
--- a/bsv.asm
+++ b/bsv.asm
@@ -236,14 +236,13 @@ init:
         ; to the PWM frequency, we can use a much faster clock for PWM. The
         ; highest "carrier frequency" for the PCM samples we can generate is by
         ; setting Timer2 to 6 bit, (IHRC/1)/1 mode, giving a frequency of
-        ; (4*4.096MHz)/2^6 = 256kHz.
+        ; (4*4.096MHz)/2^6 = 256kHz. We really use (4*4.096MHz)/2^8 = 64kHz.
 	MOV	pwm, a		; clear
 	MOV	tm2b, a		; clear
 	MOV	a, #(( 2<<4 | 3<<2 | 1<<1 | 0<<0 ))
 	MOV	tm2c, a		; timer2: IHRC, PA4, PWM, not inverted
-	MOV	a, #(( 0<<7 | 1<<5 | 0<<0 ))
+	MOV	a, #(( 0<<7 | 0<<5 | 0<<0 ))
 	MOV	tm2s, a		; 8bit, /4 prescaler, divide by (0+1)
-	;XXX: increase pwm base frequency (/1) -> (4*4.096mhz)/(2^8) = 64khz
 
 	;timer16/ivr setup
 	MOV	a, #(( 0<<0 | 1<<3 | 4<<5 ))	; ovf@bit8 (512cy; §9.2.5), clk/4, ihrc