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meeblip-micro.asm
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meeblip-micro.asm
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;-------------------------------------------------------------------------------------------------------------------
; _ _ _
; | | | |(_)
; ____ _____ _____| |__ | | _ ____ ___ _____
; | \| ___ | ___ | _ \| || | _ \ /___) ___ |
; | | | | ____| ____| |_) ) || | |_| | |___ | ____|
; |_|_|_|_____)_____)____/ \_)_| __/ (___/|_____)
; |_|
;
; meeblip se micro - the hackable digital synthesiser
;
; For meeblip micro hardware
;
;-------------------------------------------------------------------------------------------------------------------
;
; Changelog
;
;V2.04 2012.01.05 - Added maximum resonance table
; - Envelopes no longer restart on note off release if they're stopped
; - Replace MUL8X8S routine with hardware multiply
; - Updated LPM calls throughout code
; - Implement 2 byte offsets for all table lookups
; - New bandlimited waveforms with matched average amplitude (Axel Werner)
; - New 32x16 bit multiply, 32 bit load (AW)
; - Use signed multiply in DCA (AW)
; - New oscillator mix routine (AW)
; - New TAB_VCF, TAB_VCA and TIMETORATE tables (AW)
; - Fix envelope decay bug (AW)
;V2.03 2011.12.20 - Added MIDI Velocity to VCF Envelope Modulation
; - Changed maximum resonance and resonance scaling limits
; - Updated oscillator mix levels because of mix clipping
;V2.02 2011.12.12 - Corrected code to save pre-filtered waveform
;V2.01 2011.12.01 - Added inverse sawtooth waveform
; - Fixed wavetable overflow in variable pulse calculation
; - Assign individual switches instead of switch matrix
; - Synthesis engine defaults to MIDI channel 1
; - Enable patch load/save and MIDI save functions (careful with V1 hardware - you have to use the DIP switches)
; - Increase Portamento rate
; - Debugged MIDI CC switch loading routine
; - Removed unnecessary opcodes throughout code
;V2.00 2011.11.23 - Bandlimited pulse and PWM wave built from out-of-phase ramps
; - Bandlimited square, saw and triangle oscillators
; - Patch state engine (independent of front panel controls)
; - New knob scan routine (scans only the most recently converted analog channel)
; - Dual ADSD envelopes
; - PWM sweep switch and PWM rate knob (limited between 0-50% pulse duty cycle)
; - Filter envelop amount knob added
; - MIDI control of all parameters
; - Reorganized front panel
; - MIDI knob and switch CC control
; - DCA gate, LFO sync, modulation wheel and filter key track now always on
; - LFO enable switch added
; - anti-alias switch added - off uses bandlimited wave 0, on uses bandlimited wavetable 0..11, based on note
; - Added variable names for switches instead of using bit ops - allows easier reorganization of panel
; - FM switch - off or 100%
; - New sample rate - 36363.63636 Hz, approximately 440 instructions per sample
;V1.05 2011.02.04 - Save dual parameter knob values to eeprom and reload on power up.
;V1.04 2011.01.19 - MIDI CC RAM table added.
; - PWM waveform with dedicated fixed sweep LFO
; - 8-bit multiplies optimized in main loop
; - LFO Sync switch now retriggers LFO on each keypress
; - Initialize FM Depth to zero on power up
;V1.03 - VCA and VCF level tables extended to reduce stairstepping
;V1.02 - Flip DAC write line high immediately after outputting sample
;V1.01 - Optimized DCOA+DCOB summer, outputs signed value
;V1.00 - Power/MIDI status LED remains on unless receiving MIDI
; - Sustain level of ADSR envelope is exponentially scaled
; - Non-resonant highpass filter implemented
; - Filter Q level compensation moved outside audio sample calc interrupt
; - Filter calculations increased to 16x8-bit to reduce noise floor
; - DCA output level calculations are rounded
; - Mod wheel no longer overrides LFO level knob when less than knob value
;V0.90 - Initial release
;
;-------------------------------------------------------------------------------------------------------------------
;
; MeeBlip Contributors
;
; Jarek Ziembicki - Created the original AVRsynth, upon which this project is based.
; Laurie Biddulph - Worked with Jarek to translate his comments into English, ported to Atmega16
; Daniel Kruszyna - Extended AVRsynth (several of his ideas are incorporated in MeeBlip)
; Julian Schmidt - Original filter algorithm
; Axel Werner - Code optimization, bug fixes and bandlimited waveforms
; James Grahame - Ported and extended the AVRsynth code to MeeBlip hardware.
;
;-------------------------------------------------------------------------------------------------------------------
;
; Port Mapping
;
; PA0..7 8 potentiometers
; PB0-PB4 Control Panel Switches - ROWS
; PB5-PB7 ISP programming header
; PB7 DAC LDAC signal (load both DAC ports synchronously)
; PC0-PC7 DATA port for DAC
; PD0 RxD (MIDI IN)
; PD1 Power ON/MIDI LED
; PD2 Select DAC port A or B
; PD3 DAC Write line
; PD4-PD7 Control Panel Switches - COLUMNS
;
; Timers
;
; Timer0 not used
; Timer1 Time counter: CK/400 --> TCNT1
; Timer2 Sample timer: (CK/8) / 32 --> 36363.63636 Hz
;
;-------------------------------------------------------------------------------------------------------------------
.NOLIST
; .INCLUDE "m32def.inc"
.LIST
.LISTMAC
.SET cpu_frequency = 16000000
.SET baud_rate = 31250
.SET KBDSCAN = 6250
;
;-------------------------------------------------------------------------------------------------------------------
; V A R I A B L E S & D E F I N I T I O N S
;-------------------------------------------------------------------------------------------------------------------
;registers:
;current phase of DCO A:
.DEF PHASEA_0 = r2
.DEF PHASEA_1 = r3
.DEF PHASEA_2 = r4
;current phase of DCO B:
.DEF PHASEB_0 = r5
.DEF PHASEB_1 = r6
.DEF PHASEB_2 = r7
.DEF ZERO = r8
;DCF:
.def a_L = r9
.def a_H = r10
.def temp_SREG = r11
.def z_L = r18
.def z_H = r19
.def temp = r30
.def temp2 = r31
.DEF OSC_OUT_L = r14 ; pre-filter audio
.DEF OSC_OUT_H = r15
.def LDAC = r16
.def HDAC = r17
;RAM (0060h...025Fh):
.DSEG
;MIDI:
MIDIPHASE: .BYTE 1
MIDICHANNEL: .BYTE 1
MIDIDATA0: .BYTE 1
MIDIVELOCITY: .BYTE 1
MIDINOTE: .BYTE 1
MIDINOTEPREV: .BYTE 1 ; buffer for MIDI note
MIDIPBEND_L: .BYTE 1 ;\
MIDIPBEND_H: .BYTE 1 ;/ -32768..+32766
;current sound parameters:
LFOLEVEL: .BYTE 1 ; 0..255
KNOB_SHIFT: .BYTE 1 ; 0= unchanged 255= changed state
POWER_UP: .BYTE 1 ; 255 = Synth just turned on, 0 = normal operation
KNOB0_STATUS: .BYTE 1 ; Each byte corresponds to a panel knob.
KNOB1_STATUS: .BYTE 1 ; 0 = pot not updated since Knob Shift switch change
KNOB2_STATUS: .BYTE 1 ; 1 = pot has been updated.
KNOB3_STATUS: .BYTE 1
KNOB4_STATUS: .BYTE 1
KNOB5_STATUS: .BYTE 1
KNOB6_STATUS: .BYTE 1
KNOB7_STATUS: .BYTE 1
SWITCH1: .BYTE 1
SWITCH2: .BYTE 1
OLD_SWITCH1: .BYTE 1 ; Previous switch values (used to flag switch changes)
OLD_SWITCH2: .BYTE 1
; Switch value currently used (from front panel, MIDI or last loaded patch)
PATCH_SWITCH1: .BYTE 1
.equ SW_KNOB_SHIFT = 0
.equ SW_OSC_FM = 1
.equ SW_LFO_RANDOM = 2
.equ SW_LFO_WAVE = 3
.equ SW_FILTER_MODE = 4
.equ SW_DISTORTION = 5
.equ SW_LFO_ENABLE = 6
.equ SW_LFO_DEST = 7
PATCH_SWITCH2: .BYTE 1
.equ SW_ANTI_ALIAS = 0
.equ SW_OSCB_OCT = 1
.equ SW_OSCB_ENABLE = 2
.equ SW_OSCB_WAVE = 3
.equ SW_SUSTAIN = 4
.equ SW_OSCA_NOISE = 5
.equ SW_PWM_SWEEP = 6
.equ SW_OSCA_WAVE = 7
SWITCH3: .BYTE 1 ; b0: MIDI SWITCH 1
; b1: MIDI SWITCH 2
; b2: MIDI SWITCH 3
; b3: MIDI SWITCH 4
SETMIDICHANNEL: .BYTE 1 ; selected MIDI channel: 0 for OMNI or 1..15
DETUNEB_FRAC: .BYTE 1 ;\
DETUNEB_INTG: .BYTE 1 ;/ -128,000..+127,996
ATTACKTIME: .BYTE 1 ; 0..255
DECAYTIME: .BYTE 1 ; 0..255
SUSTAINLEVEL: .BYTE 1 ; 0/255
RELEASETIME: .BYTE 1 ; 0..255
ATTACKTIME2: .BYTE 1 ; 0..255
DECAYTIME2: .BYTE 1 ; 0..255
SUSTAINLEVEL2: .BYTE 1 ; 0/255
RELEASETIME2: .BYTE 1 ; 0..255
NOTE_L: .BYTE 1
NOTE_H: .BYTE 1
NOTE_INTG: .BYTE 1
PORTACNT: .BYTE 1 ; 2 / 1 / 0
LPF_I: .BYTE 1
HPF_I: .BYTE 1
LEVEL: .BYTE 1 ; 0..255
PITCH: .BYTE 1 ; 0..96
ADC_CHAN: .BYTE 1 ; 0..7
PREV_ADC_CHAN: .BYTE 1 ; 0..7
ADC_0: .BYTE 1 ; Panel knob values.
ADC_1: .BYTE 1
ADC_2: .BYTE 1
ADC_3: .BYTE 1
ADC_4: .BYTE 1
ADC_5: .BYTE 1
ADC_6: .BYTE 1
ADC_7: .BYTE 1
OLD_ADC_0: .BYTE 1 ; Previous panel knob value
OLD_ADC_1: .BYTE 1
OLD_ADC_2: .BYTE 1
OLD_ADC_3: .BYTE 1
OLD_ADC_4: .BYTE 1
OLD_ADC_5: .BYTE 1
OLD_ADC_6: .BYTE 1
OLD_ADC_7: .BYTE 1
GATE: .BYTE 1 ; 0 / 1
GATEEDGE: .BYTE 1 ; 0 / 1
TPREV_KBD_L: .BYTE 1
TPREV_KBD_H: .BYTE 1
TPREV_L: .BYTE 1
TPREV_H: .BYTE 1
DELTAT_L: .BYTE 1 ;\ Time from former course
DELTAT_H: .BYTE 1 ;/ of the main loop (1 bit = 32 µs)
ENVPHASE: .BYTE 1 ; 0=stop 1=attack 2=decay 3=sustain 4=release
ENV_FRAC_L: .BYTE 1
ENV_FRAC_H: .BYTE 1
ENV_INTEGR: .BYTE 1
ENVPHASE2: .BYTE 1 ; 0=stop 1=attack 2=decay 3=sustain 4=release
ENV_FRAC_L2: .BYTE 1
ENV_FRAC_H2: .BYTE 1
ENV_INTEGR2: .BYTE 1
VELOCITY_ENVMOD: .BYTE 1
LFOPHASE: .BYTE 1 ; 0=up 1=down
LFO_FRAC_L: .BYTE 1 ;\
LFO_FRAC_H: .BYTE 1 ; > -128,000..+127,999
LFO_INTEGR: .BYTE 1 ;/
LFOVALUE: .BYTE 1 ; -128..+127
LFO2PHASE: .BYTE 1 ; 0=up 1=down
LFO2_FRAC_L: .BYTE 1 ;\
LFO2_FRAC_H: .BYTE 1 ; > -128,000..+127,999
LFO2_INTEGR: .BYTE 1 ;/
LFO2VALUE: .BYTE 1 ; -128..+127
OLDWAVEA: .BYTE 1
OLDWAVEB: .BYTE 1
SHIFTREG_0: .BYTE 1 ;\
SHIFTREG_1: .BYTE 1 ; > shift register for
SHIFTREG_2: .BYTE 1 ;/ pseudo-random generator
LFOBOTTOM_0: .BYTE 1 ;\
LFOBOTTOM_1: .BYTE 1 ; > bottom level of LFO
LFOBOTTOM_2: .BYTE 1 ;/
LFOTOP_0: .BYTE 1 ;\
LFOTOP_1: .BYTE 1 ; > top level of LFO
LFOTOP_2: .BYTE 1 ;/
LFO2BOTTOM_0: .BYTE 1 ;\
LFO2BOTTOM_1: .BYTE 1 ; > bottom level of LFO2
LFO2BOTTOM_2: .BYTE 1 ;/
LFO2TOP_0: .BYTE 1 ;\
LFO2TOP_1: .BYTE 1 ; > top level of LFO2
LFO2TOP_2: .BYTE 1 ;/
DCOA_LEVEL: .BYTE 1
DCOB_LEVEL: .BYTE 1
KNOB_DEADZONE: .BYTE 1
; increase phase for DCO A
DELTAA_0: .byte 1
DELTAA_1: .byte 1
DELTAA_2: .byte 1
; increase phase for DCO B
DELTAB_0: .byte 1
DELTAB_1: .byte 1
DELTAB_2: .byte 1
; Wavetable select
WAVETABLE_A: .byte 1 ; Bandlimited wavetable 0..11
WAVETABLE_B: .byte 1 ; Bandlimited wavetable 0..11
; oscillator pulse width
PULSE_WIDTH: .byte 1
PULSE_KNOB_LIMITED: .byte 1
; fm
WAVEB: .byte 1
FMDEPTH: .byte 1
; eeprom
WRITE_MODE: .byte 1
WRITE_OFFSET: .byte 1 ; byte 0..15 of the patch
WRITE_PATCH_OFFSET: .byte 1 ; start of patch in eeprom
; filter
SCALED_RESONANCE: .byte 1
b_L: .byte 1
b_H: .byte 1
VCF_STATUS: .byte 1 ; 0 indicates VCF off, 1 = on
;-------------------------------------------------------------------------------------------------------------------
; MIDI Control Change parameter table
;-------------------------------------------------------------------------------------------------------------------
;
; MIDI CC parameters with an offset from MIDICC. They are automatically
; stored for use, just use the variable name to access their value.
MIDICC: .byte $80
.equ MIDIMODWHEEL = MIDICC + $01
; Unshifted knobs (potentiometer 0 through 7)
.equ RESONANCE = MIDICC + $30
.equ CUTOFF = MIDICC + $31
.equ LFOFREQ = MIDICC + $32
.equ PANEL_LFOLEVEL = MIDICC + $33
.equ VCFENVMOD = MIDICC + $34
.equ PORTAMENTO = MIDICC + $35
.equ PULSE_KNOB = MIDICC + $36
.equ OSC_DETUNE = MIDICC + $37
; Shifted knobs (potentiometer 0 through 7)
;.equ X = MIDICC + $38
;.equ X = MIDICC + $39
.equ KNOB_DCF_DECAY = MIDICC + $3A
.equ KNOB_DCF_ATTACK = MIDICC + $3B
.equ KNOB_AMP_DECAY = MIDICC + $3C
.equ KNOB_AMP_ATTACK = MIDICC + $3D
.equ SW1 = MIDICC + $3E ; Reserved
.equ SW2 = MIDICC + $3F ; Reserved
; Panel switches 0..15
; Switches 2
.equ S_KNOB_SHIFT = MIDICC + $40
.equ S_OSC_FM = MIDICC + $41
.equ S_LFO_RANDOM = MIDICC + $42
.equ S_LFO_WAVE = MIDICC + $43
.equ S_FILTER_MODE = MIDICC + $44
.equ S_DISTORTION = MIDICC + $45
.equ S_LFO_ENABLE = MIDICC + $46
.equ S_LFO_DEST = MIDICC + $47
; Switches 1
.equ S_ANTI_ALIAS = MIDICC + $48
.equ S_OSCB_OCT = MIDICC + $49
.equ S_OSCB_ENABLE = MIDICC + $4A
.equ S_OSCB_WAVE = MIDICC + $4B
.equ S_SUSTAIN = MIDICC + $4C
.equ S_OSCA_NOISE = MIDICC + $4D
.equ S_PWM_SWEEP = MIDICC + $4E
.equ S_OSCA_WAVE = MIDICC + $4F
; Patch save/load and MIDI channel set
LED_STATUS: .byte 1 ; off/on status of front panel LED
LED_TIMER: .byte 1 ; number of blinks before reset
BUTTON_STATUS: .byte 1 ; MIDI=1, SAVE=3, LOAD=7, CLEAR=0
CONTROL_SWITCH: .byte 1 ; Last panel switch moved: 1..16, where zero indicates no movement.
;-------------------------------------------------------------------------------------------------------------------
;stack: 0x0A3..0x25F
.ESEG
;-------------------------------------------------------------------------------------------------------------------
; V E C T O R T A B L E
;-------------------------------------------------------------------------------------------------------------------
.CSEG
jmp RESET ; RESET
jmp IRQ_NONE ; INT0
jmp IRQ_NONE ; INT1
jmp IRQ_NONE ; INT2
jmp TIM2_CMP ; TIMEr2 COMP
jmp IRQ_NONE ; TIMEr2 OVF
jmp IRQ_NONE ; TIMEr1 CAPT
jmp IRQ_NONE ; TIMEr1 COMPA
jmp IRQ_NONE ; TIMEr1 COMPB
jmp IRQ_NONE ; TIMEr1 OVF
jmp IRQ_NONE ; TIMEr0 COMPA
jmp IRQ_NONE ; TIMEr0 OVF
jmp IRQ_NONE ; SPI,STC
jmp UART_RXC ; UART, RX COMPLETE
jmp IRQ_NONE ; UART,UDRE
jmp IRQ_NONE ; UART, TX COMPLETE
jmp IRQ_NONE ; ADC CONVERSION COMPLETE
jmp IRQ_NONE ; EEPROM READY
jmp IRQ_NONE ; ANALOG COMPARATOR
jmp IRQ_NONE ; 2-Wire Serial Interface
jmp IRQ_NONE ; STORE PROGRAM MEMORY READY
IRQ_NONE:
reti
;-------------------------------------------------------------------------------------------------------------------
; R O M T A B L E S
;-------------------------------------------------------------------------------------------------------------------
;
; Phase Deltas at 36363.63636 Hz sample rate
;
; NOTE PHASE DELTA = 2 ^ 24 * Freq / SamplingFreq
; So... Note zero calc: 2 ^ 24 * 8.175799 / 36363.63636 = 3772.09651 (stored as 00 0E BC.19)
;
;-------------------------------------------------------------------------------------------------------------------
DELTA_C:
.DW 0xBC19 ;\
.DW 0x000E ;/ note 0 ( 8.175799 Hz)
DELTA_CIS:
.DW 0x9C66 ;\
.DW 0x000F ;/ note 1 ( 8.661957 Hz)
DELTA_D:
.DW 0x8A09 ;\
.DW 0x0010 ;/ note 2 ( 9.177024 Hz)
DELTA_DIS:
.DW 0x85CE ;\
.DW 0x0011 ;/ note 3 ( 9.722718 Hz)
DELTA_E:
.DW 0x908B ;\
.DW 0x0012 ;/ note 4 (10.300861 Hz)
DELTA_F:
.DW 0xAB25 ;\
.DW 0x0013 ;/ note 5 (10.913382 Hz)
DELTA_FIS:
.DW 0xD68D ;\
.DW 0x0014 ;/ note 6 (11.562326 Hz)
DELTA_G:
.DW 0x13C2 ;\
.DW 0x0016 ;/ note 7 (12.249857 Hz)
DELTA_GIS:
.DW 0x63D4 ;\
.DW 0x0017 ;/ note 8 (12.978272 Hz)
DELTA_A:
.DW 0xC7E3 ;\
.DW 0x0018 ;/ note 9 (13.750000 Hz)
DELTA_AIS:
.DW 0x411D ;\
.DW 0x001A ;/ note 10 (14.567618 Hz)
DELTA_H:
.DW 0xD0C5 ;\
.DW 0x001B ;/ note 11 (15.433853 Hz)
DELTA_C1:
.DW 0x7831 ;\
.DW 0x001D ;/ note 12 (16.351598 Hz)
;-----------------------------------------------------------------------------
;
; Lookup Tables
;
; VCF filter cutoff - 128 bytes
; Time to Rate table for calculating amplitude envelopes - 64 bytes
; VCA non-linear level conversion - 256 bytes
;
;-----------------------------------------------------------------------------
; VCF Filter Cutoff
;
; value = (16th root of 2)**(index+1)
;
TAB_VCF:
.db 1, 1, 1, 1, 1, 1, 1, 1 ; 0
.db 1, 1, 1, 1, 1, 1, 1, 2 ; 8
.db 2, 2, 2, 2, 2, 2, 2, 2 ; 16
.db 2, 3, 3, 3, 3, 3, 3, 3 ; 24
.db 4, 4, 4, 4, 4, 5, 5, 5 ; 32
.db 5, 6, 6, 6, 7, 7, 7, 7 ; 40
.db 8, 8, 9, 9, 9, 10, 10, 11 ; 48
.db 11, 12, 12, 13, 14, 14, 15, 16 ; 56
.db 16, 17, 18, 19, 19, 20, 21, 22 ; 64
.db 23, 24, 25, 26, 28, 29, 30, 31 ; 72
.db 33, 34, 36, 38, 39, 41, 43, 45 ; 80
.db 47, 49, 51, 53, 56, 58, 61, 63 ; 88
.db 66, 69, 72, 76, 79, 82, 86, 90 ; 96
.db 94, 98, 103, 107, 112, 117, 122, 127 ; 104
.db 133, 139, 145, 152, 158, 165, 173, 181 ; 112
.db 189, 197, 206, 215, 224, 234, 245, 255 ; 120
;-----------------------------------------------------------------------------
;Time to Rate conversion table for envelope timing.
; lfo:
; update values for 32us update rate
; LFO_INTEGR overflows all 256*32us = 8.192 ms
;
; formula Tof = 256*32us*2^16/N
; LFOfreq = 1/Tof
; Rate value = Rmin * Q^i with Q = (Rmax/Rmin)^(1/31) = 1,286111766
TIMETORATE:
.DW 50957 ; 10.54 mS fast lfo, attack/rise time
.DW 39621 ; 13.55 mS
.DW 30807 ; 17.43 mS
.DW 23953 ; 22.41 mS
.DW 18625 ; 28.83 mS
.DW 14481 ; 37.07 mS
.DW 11260 ; 47.68 mS
.DW 8755 ; 61.32 mS
.DW 6807 ; 78.87 mS
.DW 5293 ; 101.4 mS
.DW 4115 ; 130.5 mS
.DW 3200 ; 167.8 mS
.DW 2488 ; 215.8 mS
.DW 1935 ; 277.5 mS
.DW 1504 ; 356.9 mS
.DW 1170 ; 459.0 mS
.DW 909 ; 590.4 mS
.DW 707 ; 759.3 mS
.DW 550 ; 976.5 mS
.DW 427 ; 1.256 S
.DW 332 ; 1.615 S
.DW 258 ; 2.077 S
.DW 201 ; 2.672 S
.DW 156 ; 3.436 S
.DW 121 ; 4.419 S
.DW 94 ; 5.684 S
.DW 73 ; 7.310 S
.DW 57 ; 9.401 S
.DW 44 ; 12.09 S
.DW 35 ; 15.55 S
.DW 27 ; 20.00 S
.DW 19 ; 28.26 S slow lfo, attack/rise time
;-----------------------------------------------------------------------------
;
; VCA non-linear level conversion
;
; Amplitude level lookup table. Envelopes levels are calculated as linear
; and then converted to approximate an exponential saturation curve.
;
; polynomial y = a + bx + cx2 + dx3
; with coefficients
; a 0
; b 0.210841569
; c 0.000177823
; d 1.14E-05
TAB_VCA:
.db 0, 0, 0, 1, 1, 1, 1, 1 ; 0
.db 2, 2, 2, 2, 3, 3, 3, 3 ; 8
.db 3, 4, 4, 4, 4, 5, 5, 5 ; 16
.db 5, 6, 6, 6, 6, 7, 7, 7 ; 24
.db 7, 8, 8, 8, 8, 9, 9, 9 ; 32
.db 9, 10, 10, 10, 11, 11, 11, 11 ; 40
.db 12, 12, 12, 13, 13, 13, 14, 14 ; 48
.db 14, 15, 15, 15, 16, 16, 16, 17 ; 56
.db 17, 18, 18, 18, 19, 19, 20, 20 ; 64
.db 20, 21, 21, 22, 22, 23, 23, 23 ; 72
.db 24, 24, 25, 25, 26, 26, 27, 27 ; 80
.db 28, 28, 29, 29, 30, 30, 31, 31 ; 88
.db 32, 33, 33, 34, 34, 35, 35, 36 ; 96
.db 37, 37, 38, 39, 39, 40, 41, 41 ; 104
.db 42, 43, 43, 44, 45, 45, 46, 47 ; 112
.db 48, 48, 49, 50, 51, 51, 52, 53 ; 120
.db 54, 55, 56, 56, 57, 58, 59, 60 ; 128
.db 61, 62, 63, 63, 64, 65, 66, 67 ; 136
.db 68, 69, 70, 71, 72, 73, 74, 75 ; 144
.db 76, 77, 78, 80, 81, 82, 83, 84 ; 152
.db 85, 86, 87, 89, 90, 91, 92, 93 ; 160
.db 95, 96, 97, 98, 100, 101, 102, 104 ; 168
.db 105, 106, 108, 109, 110, 112, 113, 115 ; 176
.db 116, 118, 119, 120, 122, 123, 125, 126 ; 184
.db 128, 130, 131, 133, 134, 136, 138, 139 ; 192
.db 141, 142, 144, 146, 148, 149, 151, 153 ; 200
.db 154, 156, 158, 160, 162, 164, 165, 167 ; 208
.db 169, 171, 173, 175, 177, 179, 181, 183 ; 216
.db 185, 187, 189, 191, 193, 195, 197, 199 ; 224
.db 201, 203, 206, 208, 210, 212, 214, 217 ; 232
.db 219, 221, 224, 226, 228, 231, 233, 235 ; 240
.db 238, 240, 243, 245, 247, 250, 252, 255 ; 248
;-----------------------------------------------------------------------------
;
; Limit maximum resonance when filter cutoff is extremely low
;
TAB_REZ:
.db 224, 224, 224, 224, 224, 224, 224, 224 ; 0 - Low value of DE
.db 224, 228, 232, 236, 240, 244, 248, 252 ; 8 - High value of FC
;-------------------------------------------------------------------------------------------------------------------
; I N T E R R U P T S U B R O U T I N E S
;-------------------------------------------------------------------------------------------------------------------
; Timer 2 compare interrupt (sampling)
;
; This is where sound is generated. This interrupt is called 36,363 times per second
; to calculate a single 16-bit value for audio output. There are ~440 instruction cycles
; (16MHZ/36,363) between samples, and these have to be shared between this routine and the
; main program loop that scans controls, receives MIDI commands and calculates envelope,
; LFO, and DCA/DCF levels.
;
; If you use too many clock cycles here there won't be sufficient time left over for
; general housekeeping tasks. The result will be sluggish and lost notes, weird timing and sadness.
;-------------------------------------------------------------------------------------------------------------------
; Push contents of registers onto the stack
;
TIM2_CMP:
push r16
in r16, SREG ;\
push r16 ;/ push SREG
push r17
push r18
push r19
push r20
push r21
push r22
push r23
push r30
push r31
push r0
push r1
lds r21, PATCH_SWITCH1 ; Load the mode flag settings so we can check the selected waveform,
lds r23, PATCH_SWITCH2 ; noise and distortion settings.
;-------------------------------------------------------------------------------------------------------------------
;
; Oscillator A & B
;
; This design uses direct frequency synthesis to generate a ramp wave. A three-byte counter (= phase) is being
; incremented by a value which is proportional to the sound frequency (= phase delta). The
; increment takes place every sampling period. The most significant byte of the counter is a sawtooth ramp.
; This is either used as a pointer to a 256 byte wavetable or for direct waveform synthesis.
; Each oscillator has its own phase and phase delta registers. The contents of each phase delta
; register depends on the frequency being generated:
;
; PHASE DELTA = 2 ^ 24 * Freq / SamplingFreq
;
; where:
; SamplingFreq = 40000 Hz
; Freq = 440 * 2 ^ ((n - 69 + d) / 12)
; where in turn:
; n = MIDI note number. Range limited to 36 to 96 (5 octaves)
; d = transpose/detune (in halftones)
;
;-------------------------------------------------------------------------------------------------------------------
;Calculate DCO A
; If Noise switch is on, use pseudo-random shift register value
sbrs r23, SW_OSCA_NOISE ; Use noise if bit set, otherwise jump to calculate DCO.
rjmp CALC_DCOA
lds r17, SHIFTREG_2
sbrc PHASEA_2,3
com r17
sbrc PHASEA_2,4
com r17
sbrc PHASEA_2,6
com r17
sbrc PHASEA_2,7
com r17
lsl r17
rjmp CALC_DCOB ; skip sample calc for DCO A if noise bit set
CALC_DCOA:
mov r17, PHASEA_2 ; sawtooth ramp for OSCA
sbrs r23, SW_OSCA_WAVE ; 0/1 (DCO A = saw/pwm)
rjmp DCOA_SAW
;Pulse wave generated by subtracting two bandlimited sawtooths, between 0 and 180 degrees out of phase
sbrs r23, SW_PWM_SWEEP
lds r20, PULSE_KNOB_LIMITED ; PWM Sweep switch is off, so load the knob value as PWM width
sbrc r23, SW_PWM_SWEEP
lds r20, PULSE_WIDTH ; PWM Sweep switch is on, load pulse width from LF02
sbrs r23, SW_ANTI_ALIAS
rjmp RAW_PULSE ; Calculate raw pulse/PWM when anti-alias switch is off
lds r22, WAVETABLE_A ; Offset to the correct wavetable, based on note number (0..15)
; r17 phase
; r20 pulse width
; r22 wavetable
; get sample a into r17
ldi ZL, low (2*INV_SAW0) ; Load low part of byte address into ZL
ldi ZH, high(2*INV_SAW0) ; Load high part of byte address into ZH
add ZL, r17 ; Offset the wavetable by the ramp phase (i)
adc ZH, r22 ; Wavetable 0..15
lpm ; Load wave(i) into r0
; get sample b out of phase into r18
mov r16, r20 ; Grab a copy of the pulse width
add r16, r17 ; Add phase offset for second table (pulse width + original sample)
mov r17, r0 ; store previous sample in r17
ldi ZL, low (2*INV_SAW0) ; Load low part of byte address into ZL
ldi ZH, high(2*INV_SAW0) ; Load high part of byte address into ZH
add ZL, r16 ; Add phase offset for second table.
adc ZH, r22 ; Wavetable 0..15
lpm ; Load wave(i) into r0
; subtract wave a-b
; first part b > a, second part b < a
clr r16
sub r17, r0
sbc r16, ZERO
add r17, r20 ; add offset (pulse width)
adc r16, ZERO
brge PULSE_BOUND_CHECK ; non-negative result, so no need to limit the value
ldi r17, 0
ldi r16, 0 ; value was negative, so force to zero
PULSE_BOUND_CHECK:
tst r16 ; Check if we're larger than 255
breq PWM_EXIT ; no need to limit upper bound
ldi r17, $FF
PWM_EXIT:
subi r17, $80 ; sign the result
rjmp CALC_DCOB
; Raw Pulse wave generated on the fly. Aliases like crazy (calc'd only when anti-alias switch is OFF)
RAW_PULSE:
cp r17, r20
brlo PULSE_ZERO
ldi r17, 255
subi r17, $80 ; Sign the sample
rjmp CALC_DCOB
PULSE_ZERO:
ldi r17, 0
subi r17, $80 ; Sign the sample
rjmp CALC_DCOB
; Calculate DCOA sawtooth
DCOA_SAW:
mov r17, PHASEA_2
sbrs r23, SW_ANTI_ALIAS
rjmp DCOA_SAW_SIGN
lds r22, WAVETABLE_A ; Offset to the correct wavetable, based on note number (0..15)
ldi ZL, low (2*INV_SAW0) ; Load low part of byte address into ZL
ldi ZH, high(2*INV_SAW0) ; Load high part of byte address into ZH
add ZL, r17 ; Offset the wavetable by the ramp phase (i)
adc ZH, r22 ; Wavetable 0..15
lpm ; Load wave(i) into r0
mov r17, r0 ; Copy into DCO B
DCOA_SAW_SIGN:
subi r17, $80 ; -127..127 Sign oscillator
;Calculate DCO B
CALC_DCOB:
lds r22, WAVETABLE_B ; Offset to the correct wavetable, based on note number (0..15)
sbrs r23, SW_ANTI_ALIAS
ldi r22, 0 ; Use wavetable 0 when anti-alias switch off
mov r16, PHASEB_2 ; Use ramp value as offset when scanning wavetable
sbrs r23, SW_OSCB_WAVE ; 0/1 (DCO B = saw/squ)
rjmp LIMITED_TRIB
LIMITED_SQB: ; Square wave lookup
ldi ZL, low(2*SQ_LIMIT0) ; Load low part of byte address into ZL
ldi ZH, high(2*SQ_LIMIT0) ; Load high part of byte address into ZH
add ZL, r16 ; Offset the wavetable by the ramp phase (i)
adc ZH, r22 ; Wavetable 0..15
lpm ; Load wave(i) into r0
mov r16, r0 ; Copy into DCO B
rjmp CALC_DIST
LIMITED_TRIB: ; Triangle wave lookup
ldi ZL, low(2*TRI_LIMIT0) ; Load low part of byte address into ZL
ldi ZH, high(2*TRI_LIMIT0) ; Load high part of byte address into ZH
add ZL, r16 ; Offset the wavetable by the ramp phase (i)
adc ZH, r22 ; Wavetable 0..15
lpm ; Load wave(i) into r0
mov r16, r0 ; Copy into DCO B
CALC_DIST:
subi r16, $80 ; -127..127 Sign Oscillator B waveform
sbrc r21, SW_DISTORTION ; 0/1 (OSC DIST = off/on)
eor r17, r16
; Turn off OSCB if not enabled
;sbrs r23, SW_OSCB_ENABLE
;ldi r16, $00 ; Zero OSCB. Oscillator is signed
;-------------------------------------------------------------------------------------------------------------------
; Sum Oscillators
;
; Combines DCOA (in r17) and DCOB (in r16) waves to produce a 16-bit signed result in HDAC:LDAC (r17:r16)
;
sts WAVEB,r16 ; store signed DCO B wave for fm
; Mixer out = (A*x + B*(1-x))/4 x=0..1
ldi r22, $7F ; Set maximum oscillator level to 127 for each oscillator
mulsu r17, r22 ; signed DCO A wave * level
movw r30, r0 ; store value in temp register
sbrs r23, SW_OSCB_ENABLE ; if OSC B disabled add OSC A twice
mov r16, r17 ; (A*x + A*(1-x))/4 x=0..1
mulsu r16, r22 ; signed DCO B wave * level
add r30, r0
adc r31, r1 ; sum scaled waves
movw r16, r30 ; place signed output in HDAC:LDAC
; rotate right a couple of times to make a couple of bits of headroom for resonance.
asr r17 ;\
ror r16 ;/ r17:r16 = r17:r16 asr 1
asr r17 ;\
ror r16 ;/ r17:r16 = r17:r16 asr 1
movw OSC_OUT_L, r16 ; keep a copy for highpass filter
;DCF:
;-------------------------------------------------------------------------------------------------------------------
; Digitally Controlled Filter
;
; A 2-pole resonant low pass filter:
;
; a += f * ((in - a) + q * (a - b));
; b += f * (a - b);
;
; Input 16-Bit signed HDAC:LDAC (r17:r16), already scaled to minimize clipping (reduced to 25% of full code).
;-------------------------------------------------------------------------------------------------------------------
;calc (in - a) ; both signed
sub LDAC, a_L
sbc HDAC, a_H
;check for overflow / do hard clipping
brvc OVERFLOW_1 ;if overflow bit is clear jump to OVERFLOW_1
;sub overflow happened -> set to min
;b1000.0000 b0000.0001 -> min
;0b0111.1111 0b1111.1111 -> max
ldi LDAC, 0b00000001
ldi HDAC, 0b10000000
OVERFLOW_1: ;when overflow is clear
;(in-a) is now in HDAC:LDAC as signed
;now calc q*(a-b)
; Scale resonance based on filter cutoff
lds r22, SCALED_RESONANCE
lds r20, LPF_I ;load 'F' value
ldi r21, 0xff
sub r21, r20 ; 1-F
lsr r21
ldi r18, 0x08 ; changed (4 was original value in V1)
add r21, r18
sub r22, r21 ; Q-(1-f)
brcc OVERFLOW_2 ; if no overflow occured
ldi r22, 0x00 ;0x00 because of unsigned
OVERFLOW_2:
mov r20, a_L ;\
mov r21, a_H ;/ load 'a' , signed
lds z_H, b_H ;\
lds z_L, b_L ;/ load 'b', signed
sub r20, z_L ;\
sbc r21, z_H ;/ (a-b) signed
brvc OVERFLOW_3 ;if overflow is clear jump to OVERFLOW_3
;b1000.0000 b0000.0001 -> min
;0b0111.1111 0b1111.1111 -> max
ldi r20, 0b00000001
ldi r21, 0b10000000
OVERFLOW_3:
lds r18, PATCH_SWITCH1 ; Check Low Pass/High Pass panel switch.
sbrs r18, SW_FILTER_MODE
rjmp CALC_LOWPASS
SKIP_REZ:
movw z_L, r20 ; High Pass selected, so just load r21:r20 into z_H:z_L to disable Q
rjmp DCF_ADD ; Skip lowpass calc
CALC_LOWPASS:
; skip resonance calculation if VCF is turned off (value of 0)
lds r18, VCF_STATUS
tst r18
breq SKIP_REZ
; mul signed:unsigned -> (a-b) * Q
; 16x8 into 16-bit
; r19:r18 = r21:r20 (ah:al) * r22 (b)
mulsu r21, r22 ; (signed)ah * b
movw r18, r0
mul r20, r22 ; al * b
add r18, r1
adc r19, ZERO
rol r0 ; r0.7 --> Cy
brcc NO_ROUND ; LSByte < $80, so don't round up
inc r18
NO_ROUND:
clc
lsl r18
rol r19
clc
lsl r18
rol r19
movw z_L,r18 ;Q*(a-b) in z_H:z_L as signed
;add both
;both signed
;((in-a)+q*(a-b))
;=> HDAC:LDAC + z_H:z_L
DCF_ADD:
add LDAC, z_L
adc HDAC, z_H
brvc OVERFLOW_4 ;if overflow is clear
;b1000.0000 b0000.0001 -> min
;0b0111.1111 0b1111.1111 -> max
ldi LDAC, 0b11111111
ldi HDAC, 0b01111111
OVERFLOW_4:
;Result is a signed value in HDAC:LDAC
;calc * f
;((in-a)+q*(a-b))*f
lds r20, LPF_I ;load lowpass 'F' value
lds r18, PATCH_SWITCH1
sbrc r18, SW_FILTER_MODE ; Check LP/HP switch.
lds r20, HPF_I ; Switch set, so load 'F' for HP
; mul signed unsigned HDAC*F
; 16x8 into 16-bit
; r19:r18 = HDAC:LDAC (ah:al) * r20 (b)
mulsu HDAC, r20 ; (signed)ah * b
movw r18, r0
mul LDAC, r20 ; al * b
add r18, r1 ; signed result in r19:r18
adc r19, ZERO
rol r0 ; r0.7 --> Cy
brcc NO_ROUND2 ; LSByte < $80, so don't round up
inc r18
NO_ROUND2:
;Add result to 'a'
;a+=f*((in-a)+q*(a-b))
add a_L, r18
adc a_H, r19
brvc OVERFLOW_5 ;if overflow is clear
;b1000.0000 b0000.0001 -> min
;0b0111.1111 0b1111.1111 -> max
ldi z_L, 0b11111111
ldi z_H, 0b01111111
mov a_L, z_L
mov a_H, z_H
OVERFLOW_5: