; ----- Set up the initial waveform
- ; Point Z at the first waveform in the rom, X at the waveform buffer
- ldi XL, LOW(waveform)
- ldi XH, HIGH(waveform)
+ ; Point Z at the first waveform in the rom
ldi ZL, LOW(2*wavetable_begin)
ldi ZH, HIGH(2*wavetable_begin)
- ; Copy 256 bytes from program memory at Z to data at X
- ldi r25, 0x00
-_load_loop:
- lpm r24, Z+
- st X+, r24
- inc r25
- brne _load_loop
-
- ; Point X at the waveform table (table must be 256-byte aligned)
- ldi r23, 0x00 ; Fractional part
- ldi XL, LOW(waveform) ; Integer low part, must be zero
- ldi XH, HIGH(waveform) ; Integer high part
+ ; Advance waveforms to load the LUT into ram and reset the cursor
+ rcall next_waveform
; Initial step size
ldi r16, 0x00 ; Fractional part
rjmp _button_done
; Button pin status has changed
- ; ----- Advance to next waveform in rom and copy to waveform LUT
+ ; Advance to next waveform in rom and copy to waveform LUT
; Do this before the switch debouncing so the time spent copying can be
; used as part of the wait time for the switch to settle
+ rcall next_waveform
- ; Point X at the ram waveform table (Z already points at next in rom)
- ldi XL, LOW(waveform)
- ldi XH, HIGH(waveform)
+ ; Debounce, wait for button release, and debounce again
+ rcall debounce
+_button_wait_release:
+ sbis PINC, PINC5
+ rjmp _button_wait_release
+ rcall debounce
- ; Copy 256 bytes from program memory at Z to data at X
- ldi r25, 0x00
-_button_load_loop:
- lpm r24, Z+
- st X+, r24
- inc r25
- brne _button_load_loop
- cpi ZH, HIGH(2*wavetable_end)
- brne _button_load_done
- ldi ZH, HIGH(2*wavetable_begin)
-_button_load_done:
+_button_done:
+ ; --------------------------------------------------------------
- ; Point X at the waveform table (table must be 256-byte aligned)
- ldi r23, 0x00 ; Fractional part
- ldi XL, LOW(waveform) ; Integer low part, must be zero
- ldi XH, HIGH(waveform) ; Integer high part
- ; ----- Debounce - wait until pin is quiet for some duration
+ rjmp loop
-_button_reset_wait:
- sbi PCIFR, PCIF1 ; Clear pin change flag (w1c)
- sbi TIFR0, OCF0A ; Clear timer expire flag (w1c)
- ldi r25, (1 << TSM) | (1 << PSRSYNC)
- out GTCCR, r25 ; Reset prescaler and hold
- ldi r25, 0x00 ; Reset timer count value
- out TCNT0, r25
- out GTCCR, r25 ; Unhalt the prescaler to run the timer
-_button_busyloop:
- sbic PCIFR, PCIF1 ; If the pin changed again, reset the clock
- rjmp _button_reset_wait
- sbis TIFR0, OCF0A ; If the timer expired, exit the loop
- rjmp _button_busyloop
- ; ----- Wait for button release
+; ------------------------------------------------------------------------------
+; Subroutines
+
-_button_wait_release:
- sbis PINC, PINC5
- rjmp _button_wait_release
+next_waveform:
+ ; Throughout execution, Z points to the next wavetable to be loaded into
+ ; the waveform buffer. This subroutine advances the Z pointer as it
+ ; copies, and wraps it back around to the beginning of the wavetable if
+ ; it reaches the end.
- ; ----- Debounce again
+ ; Copy the next waveform from the wavetable ROM into the waveform buffer
+ ldi XL, LOW(waveform) ; Point X at the waveform buffer
+ ldi XH, HIGH(waveform)
+ ldi r25, 0x00
+_next_waveform_loop:
+ lpm r24, Z+ ; Load a byte from wavetale
+ st X+, r24 ; Store it to the waveform buffer
+ inc r25 ; Advance counter
+ brne _next_waveform_loop ; Exit when counter overflows to zero
+
+ ; Handle wrap-around after cycling through all waveforms
+ ; Waveforms are all 256 bytes long, so the lower byte of Z will always
+ ; be the same after copying, so no need to reload it
+ cpi ZH, HIGH(2*wavetable_end) ; Did we copy the final waveform?
+ brne _next_waveform_nowrap
+ ldi ZH, HIGH(2*wavetable_begin) ; If so, reset to the first waveform
+_next_waveform_nowrap:
+
+ ; Reset the current sample pointer
+ ldi r23, 0x00 ; Fractional part
+ ldi XL, LOW(waveform) ; Integer low part
+ ldi XH, HIGH(waveform) ; Integer high part
+
+ ret
+
+
+debounce:
+ ; Debouncing is done by waiting for the pin to be quiet (no transitions)
+ ; for some specified amount of time (1ms for now, see OCR0A in the init
+ ; section above).
+ ;
+ ; We run the timer for 1ms and run in a busyloop until it expires. If
+ ; during this loop the pin change flag indicates that there was a
+ ; transition, we reset the timer and wait again.
-_button_reset_wait_2:
- sbi PCIFR, PCIF1 ; Clear pin change flag (w1c)
- sbi TIFR0, OCF0A ; Clear timer expire flag (w1c)
- ldi r25, (1 << TSM) | (1 << PSRSYNC)
- out GTCCR, r25 ; Reset prescaler and hold
- ldi r25, 0x00 ; Reset timer count value
- out TCNT0, r25
- out GTCCR, r25 ; Unhalt the prescaler to run the timer
-_button_busyloop_2:
- sbic PCIFR, PCIF1 ; If the pin changed again, reset the clock
- rjmp _button_reset_wait_2
- sbis TIFR0, OCF0A ; If the timer expired, exit the loop
- rjmp _button_busyloop_2
+_debounce_reset:
+ sbi PCIFR, PCIF1 ; Ensure pin change flag is cleared (w1c)
+ sbi TIFR0, OCF0A ; Ensure timer expire flag is cleared (w1c)
-_button_done:
- ; --------------------------------------------------------------
+ ; PSRSYNC resets the timer clock prescaler
+ ; TSM forces the prescaler to be held in reset
+ ldi r25, (1 << TSM) | \
+ (1 << PSRSYNC)
+ out GTCCR, r25 ; Reset the prescaler and halt
+ ldi r25, 0x00
+ out TCNT0, r25 ; Reset timer count value
+ out GTCCR, r25 ; Unhalt the prescaler to run the timer
+_debounce_busyloop:
+ sbic PCIFR, PCIF1 ; If the pin changed again, reset and retry
+ rjmp _debounce_reset
+ sbis TIFR0, OCF0A ; IF the timer expired, exit the loop
+ rjmp _debounce_busyloop
+ ret
- rjmp loop
; ------------------------------------------------------------------------------
projects / atmega / siggen.git / commitdiff