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Not working implementation of timer-driven video signal generation

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Daniele Verducci (ZenPenguin) 2021-01-10 10:50:34 +01:00
parent 66414a2e57
commit ce23f9e799
1 changed files with 106 additions and 79 deletions
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169
pat80-io-devices/composite-pal-adapter/software/avr-assembly/main.asm
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@ -5,7 +5,7 @@
;
; INTERFACING WITH PAT80:
; Use PortB as data port. Before writing anything, issue a read (pin RW HIGH) and check the busy pin on the data port.
; If the busy pin is high, retry reading until goes low. When the busy pin goes low, we have
; If the busy pin is high, retry reading until goes low. When the busy pin goes low, we have... TODO
;
; ELECTRONICALLY:
; The data port D0 (= PB0) is tied to ground with a 1KOhm resistance. When the MC is busy drawing the screen, the data port is in
@ -19,20 +19,20 @@
;
; RESERVED REGISTERS:
; R25: Current status (what the interrupt should do when fired):
; 0, 2, 4, 6, 8 = long sync start (sync pin low and register next interrupt after 30uS)
; 1, 3, 5, 7, 9 = long sync end (sync pin high and register next interrupt after 2uS)
; 10, 12, 14, 16, 18 = short sync start (sync pin low and register next interrupt after 2uS)
; 11, 13, 15, 17, 19 = short sync end (sync pin high and register next interrupt after 30uS)
; 20 = draw lines (draw 304 lines complete with line sync and back porch, then start short
; 0, 1, 2, 3, 4 = long sync
; 5, 6, 7, 8, 9 = short sync
; 10 = draw lines (draw 304 lines complete with line sync and back porch, then start short
; sync: sync pin low and next interrupt after 2uS)
; 21, 23, 25, 27, 29 = short sync start (sync pin low and register next interrupt after 2uS)
; 22, 24, 26, 28, 30 = short sync end (sync pin high, reset R25 to 0 and register next interrupt after 30uS)
; 11, 12, 13, 14, 15, 16 = short sync
; 17-255 = invalid state or screen draw finished: set to 0 and restart from first long sync start
.include "atmega1284definition.asm"
; define constant
.equ SYNC_PIN = PC0 ; Sync pin (pin 22)
.equ DEBUG_PIN = PC1 ; DEBUG: Single vertical sync pulse to trigger oscilloscope (pin 23)
.equ TIMER_DELAY_30US = 65536 - 719 ; 719 cycles @ 24Mhz
.equ TIMER_DELAY_2US = 65536 - 48 ; 48 cycles @ 24Mhz
; memory
.equ FRAMEBUFFER = 0x100
@ -40,12 +40,12 @@
; start vector
.org 0x0000
rjmp main ; jump to main label
.org 0x0002
rjmp on_int0 ; interrupt 0
.org 0x0012
rjmp on_int1 ; interrupt for timer 1 overflow
; main program
main:
; setup
; pins setup
sbi DDRC, SYNC_PIN ; set pin as output
sbi DDRC, DEBUG_PIN ; set pin as output
ldi r16, 0xFF
@ -70,40 +70,57 @@ main:
cpi r26, 0b11000000
brne load_mem_loop ; if not 0, repeat h_picture_loop
; timer setup (use 16-bit counter TC1)
; The Power Reduction TC1 and TC3 bits in the Power Reduction Registers (PRR0.PRTIM1 and
; PRR1.PRTIM3) must be written to zero to enable the TC1 and TC3 module.
ldi r16, 0b00001000
sts PRR0, r16
ldi r16, 0b00000001
sts PRR1, r16
; Set TCNT1 (timer counter) to 0xFF00 (the timer will trigger soon)
ser r27
sts TCNT1H,r27
clr r26
sts TCNT1L,r26
; Set prescaler to 1:1 (TCCR1B is XXXXX001)
ldi r16, 0b00000001
sts TCCR1B, r16
; Enable timer1 overflow interrupt(TOIE1): the interrupt 1 will be fired when timer resets
ldi r16, 0b00000100
sts TIMSK1, r16
; The Global Interrupt Enable bit must be set for the interrupts to be enabled.
ldi r16, 0b10000000
sts SREG, r16
; loop forever
forever:
jmp forever
; ********* FUNCTIONS CALLED BY INTERRUPT ***********
on_int1:
; called by timer 1 two times per line (every 32 uS) during hsync. Disabled while drawing picture.
on_int0:
; called two times per line (every 32 uS) during hsync. Disabled while drawing picture.
; if r25 >= 32 then r25=0
cpi r25, 32
brlt switch_status
clr r25
; check status and decide what to do
switch_status:
cpi r25, 5
brlt long_sync ; 0-4: long sync
cpi r25, 10 ; 5-9: short sync
breq draw_picture ; 10: draw picture
jmp short_sync ; 11-16: short_sync
v_refresh_loop:
draw_picture:
; increment status
inc r25
; set X register to framebuffer start 0x0100
; (set it a byte before, because it will be incremented at first)
clr r27
ldi r26, 0xFF
; start 5 long sync pulses
call long_sync
call long_sync
call long_sync
call long_sync
call long_sync
; end 5 long sync pulses
; start 5 short sync pulses
call short_sync
call short_sync
call short_sync
call short_sync
call short_sync
; end 5 short sync pulses
; start 304 picture lines
ldi r17, 152 ; line counter
h_picture_loop:
@ -181,64 +198,74 @@ v_refresh_loop:
; video pin goes low before sync
clr r19 ; 1 cycle
out PORTA, r19 ; 1 cycle
; start 6 short sync pulses
call short_sync
call short_sync
call short_sync
call short_sync
call short_sync
call short_sync
; end 6 short sync pulses
; debug
; sbi PORTC, DEBUG_PIN ; high
; cbi PORTC, DEBUG_PIN ; low
; debug
jmp v_refresh_loop
; end vertical refresh
; immediately start first end-screen short sync
cbi PORTC, SYNC_PIN ; sync goes low (0v) ; 2 cycle
; set timer in 2uS:
ldi r27, high(TIMER_DELAY_2US<<1)
ldi r26, low(TIMER_DELAY_2US<<1)
sts TCNT1H,r27
sts TCNT1L,r26
reti
; end draw_picture
long_sync:
; long sync: 30uS low (719 cycles @ 24Mhz), 2uS high (48 cycles @ 24Mhz)
inc r25 ; increment status counter
sbis PORTC, SYNC_PIN ; if sync is high (sync is not occuring) skip next line
jmp long_sync_end
; sync pin is high (sync is not occuring)
cbi PORTC, SYNC_PIN ; sync goes low (0v) ; 2 cycle
; set timer in 30uS (reset timer counter)
ldi r27, high(TIMER_DELAY_30US<<1)
ldi r26, low(TIMER_DELAY_30US<<1)
sts TCNT1H,r27
sts TCNT1L,r26
reti
ldi r18, 120 ; 1 cycle
long_sync_low_loop: ; requires 6 cpu cycles
nop ; 1 cycle
nop ; 1 cycle
nop ; 1 cycle
dec r18 ; 1 cycle
brne long_sync_low_loop ; 2 cycle if true, 1 if false
long_sync_end:
; sync pin is low (sync is occuring)
sbi PORTC, SYNC_PIN ; sync goes high (0.3v)
; set timer in 2uS:
ldi r27, high(TIMER_DELAY_2US<<1)
ldi r26, low(TIMER_DELAY_2US<<1)
sts TCNT1H,r27
sts TCNT1L,r26
reti
ldi r18, 15 ; 1 cycle
long_sync_high_loop: ; requires 3 cpu cycles
dec r18 ; 1 cycle
brne long_sync_high_loop ; 2 cycle if true, 1 if false
ret
short_sync:
; short sync: 2uS low (48 cycles @ 24Mhz), 30uS high (720 cycles @ 24Mhz)
inc r25 ; increment status counter
sbis PORTC, SYNC_PIN ; if sync is high (sync is not occuring) skip next line
jmp short_sync_end
; sync pin is high (sync is not occuring)
cbi PORTC, SYNC_PIN ; sync goes low (0v) ; 2 cycle
; set timer in 2uS (reset timer counter)
ldi r27, high(TIMER_DELAY_2US<<1)
ldi r26, low(TIMER_DELAY_2US<<1)
sts TCNT1H,r27
sts TCNT1L,r26
reti
ldi r18, 15 ; 1 cycle
short_sync_low_loop: ; requires 3 cpu cycles
dec r18 ; 1 cycle
brne short_sync_low_loop ; 2 cycle if true, 1 if false
short_sync_end:
; sync pin is low (sync is occuring)
sbi PORTC, SYNC_PIN ; sync goes high (0.3v)
ldi r18, 120 ; 1 cycle
short_sync_high_loop: ; requires 6 cpu cycles
nop ; 1 cycle
nop ; 1 cycle
nop ; 1 cycle
dec r18 ; 1 cycle
brne short_sync_high_loop ; 2 cycle if true, 1 if false
ret
; set timer in 30uS:
ldi r27, high(TIMER_DELAY_30US<<1)
ldi r26, low(TIMER_DELAY_30US<<1)
sts TCNT1H,r27
sts TCNT1L,r26
reti
draw_line: