Apple-2gs-SW/iigs-game-engine
1
0
Fork 0
mirror of https://github.com/lscharen/iigs-game-engine.git synced 2024-11-21 20:30:50 +00:00
Code Issues Projects Releases Wiki Activity

Change how to calculate DOC reg values for noise channel

Browse Source
This commit is contained in:
Lucas Scharenbroich 2023-06-19 07:14:10 -05:00
parent ecb11df945
commit 01d8029125
2 changed files with 41 additions and 27 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

56
demos/smb/apu.s
View File

@ -737,29 +737,14 @@ interrupt_handler = *
lda APU_NOISE_LENGTH_COUNTER ; If the length counter is zero, no output
beq :mute_noise
rep #$30
lda APU_NOISE_CURRENT_PERIOD
cmp _apu_noise_last_period ; it's expensive to recalc frequencies, so avoid it when possible
beq :freq_end_noise
sta _apu_noise_last_period
jsr get_pulse_freq ; return freq in 16-bic accumulator
; Hack??
; lsr
; lsr
; lsr
; lsr ; LSFR produces 32768 values 1-bit at a time. We have byte samples
; so 32768 / 8 = 4096 / 256 byte = division factor of 16
sep #$30
ldx #$00+noise_oscillator
stx sound_address
lda APU_NOISE_CURRENT_PERIOD
sta sound_data
ldx #$20+noise_oscillator
stx sound_address
xba
lda APU_NOISE_CURRENT_PERIOD+1
sta sound_data
:freq_end_noise sep #$30
lda #$40+noise_oscillator
sta sound_address
@ -769,7 +754,6 @@ interrupt_handler = *
lda APU_NOISE_ENVELOPE
bra :set_volume_noise
:mute_noise
sep #$30
lda #$40+noise_oscillator
sta sound_address
lda #0
@ -808,6 +792,20 @@ set_pulse_volume
sta sound_data
rts
; This is a bit different because we actually calculate a scan rate directly to match the
; rate at which new samples are read form DOC RAM to the period of the noise channel
;
; IIgs Scan Rate (SR) = 894886 Hz / (OSC + 2) = 894886 Hz / 34 = 26320.1765 samples / sec
; IIgs Sample Rate = 51.406 * F_HL samples / sec
; We have 256 samples
; NES Noise Sample Rate = 1789772 Hz / P
;
; An as example, let P = 8, so a new sample should be output
; Solving for F_HL: F_HL = 1789772 / (51.406 * 8) = 4352
get_noise_freq
; NES freq = f_CPU / (16 * (t + 1))
; = 1.789773 MHz / (16 * (t + 1))
; = 111860.812 Hz / (t + 1)
@ -1115,10 +1113,12 @@ APU_NOISE_REG3_WRITE ENT
and #$0F
asl
tax
ldal NoisePeriodTable,x
sta APU_NOISE_CURRENT_PERIOD
ldal NoisePeriodTable+1,x
sta APU_NOISE_CURRENT_PERIOD+1
; ldal NoisePeriodTable,x
ldal EsqNoiseFreqTable,x
stal APU_NOISE_CURRENT_PERIOD
; ldal NoisePeriodTable+1,x
ldal EsqNoiseFreqTable+1,x
stal APU_NOISE_CURRENT_PERIOD+1
pla
plx
@ -1153,11 +1153,17 @@ APU_NOISE_REG4_WRITE ENT
plp
rtl
; Lookup from bottom 4 bits of NOISE_REG3
NoisePeriodTable dw 4, 8, 16, 32, 64, 96, 128, 160, 202, 254, 380, 508, 762, 1016, 2034, 4068
; Lookup from bottom 4 bits of NOISE_REG3 and pre-calculated ensoniq parameters
NoisePeriodTable dw 4, 8, 16, 32, 64, 96, 128, 160, 202, 254, 380, 508, 762, 1016, 2034, 4068
EsqNoiseFreqTable dw 8704, 4352, 2176, 1088, 544, 363, 272, 218, 172, 137, 92, 69, 46, 34, 17, 9
APU_FORCE_OFF dw 0
APU_STATUS_WRITE ENT
; ldal APU_FORCE_OFF
; bne apu_status_exit
APU_STATUS_FORCE
phb
phk
plb
@ -1194,4 +1200,6 @@ APU_STATUS_WRITE ENT
pla
plb
apu_status_exit
rtl

12
demos/smb/apu_sim.s
View File

@ -86,11 +86,17 @@ Tmp1 equ 130
brl :update
cmp #' '
bne :next
bne :not_spc
jsr Toggle
brl :update
:next
:not_spc cmp #'a'
bne :not_a
lda show_border
eor #1
sta show_border
:not_a
brl :evtloop
:done
jsr APUShutDown
@ -553,7 +559,7 @@ DrawTriangle
jsr DrawWord
ldy #TRIANGLE_REG3_STR
lda APU_PULSE2_REG3
lda APU_TRIANGLE_REG3
ldx #{{TRIANGLE_X+5}*4}+{ROW_SPAN*{TRIANGLE_Y+1}}
jsr DrawBitsHL