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Straight, but unstable image. Some unwanted spaces during vertical sync

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Daniele Verducci su MatissePenguin 2021-02-20 20:33:55 +01:00
parent 36ede10f3b
commit 33baf71cf0
2 changed files with 13 additions and 13 deletions
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2
pat80-io-devices/composite-pal-adapter/software/avr-assembly/main.asm
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@ -53,7 +53,7 @@
; memory
.equ FRAMEBUFFER = 0x0100
.equ FRAMEBUFFER_END = 0x2F00
.equ SCREEN_HEIGHT = 256
.equ SCREEN_HEIGHT = 248
; start vector
.org 0x0000

24
pat80-io-devices/composite-pal-adapter/software/avr-assembly/video_generator.asm
View File

@ -3,12 +3,12 @@
; * Video generator module *
; *******************************************
; Implemented following timings in http://blog.retroleum.co.uk/electronics-articles/pal-tv-timing-and-voltages/
; Implemented following timings in http://blog.retroleum.co.uk/electronics-articles/pal-tv-timing-and-voltages/ and http://www.kolumbus.fi/pami1/video/pal_ntsc.html
; Every line, for 46 times, it loads a byte from memory into PORTA register and then shifts the byte to the left to show another bit (do it 7 times)
; This also displays byte's MSB pixel "for free", as the video pin is PD7 (last bit of PORTA).
; This module generates a Composite PAL monochrome signal with a resolution
; of 416x304 pixels of which only 368x256 pizels are visible (= 46x29 characters).
; of 416x304 pixels of which only 368x248 pixels are visible (= 46x28 characters).
; The signal is generated using 16-bit Timer1 and interrupts.
@ -32,7 +32,7 @@
.equ TIMER_DELAY_60US = 65535 - 1409 ; 719 cycles @ 24Mhz (minus overhead)
.equ TIMER_DELAY_30US = 65535 - 690 ; 719 cycles @ 24Mhz (minus overhead)
.equ TIMER_DELAY_2US = 65535 - 17 ; 48 cycles @ 24Mhz (minus overhead)
.equ TIMER_DELAY_4US = 65535 - 64 ; 96 cycles @ 24Mhz (minus overhead)
.equ TIMER_DELAY_4US = 65535 - 60 ; 96 cycles @ 24Mhz (minus overhead)
.equ BACK_PORCH_DELAY = 234 ; 186 cycles back porch + 48 cycles to leave 2 chunks empty (image padding)
@ -43,8 +43,8 @@ on_tim1_ovf:
sbi PORTD, BUSY_PIN
; called by timer 1 two times per line (every 32 uS) during hsync, unless drawing picture.
inc STATUS
; if STATUS >= 152 then STATUS=0
cpi STATUS, 152 ; TODO: Added a seventh sync pulse at end of screen because at the first short sync after the image, the timer doesn't tick at the right time
; if STATUS > 146 then STATUS=0
cpi STATUS, 147 ; TODO: Added a seventh sync pulse at end of screen because at the first short sync after the image, the timer doesn't tick at the right time
brlo switch_status
clr STATUS
; check status and decide what to do
@ -53,12 +53,12 @@ on_tim1_ovf:
brlo long_sync ; 0-9: long sync
cpi STATUS, 20
brlo short_sync ; 10-19: short sync
cpi STATUS, 92
brlo empty_line ; 20-91: empty lines
breq start_draw_picture ; 92: draw picture
cpi STATUS, 140
brlo empty_line ; 93-139 = draw empty lines
jmp short_sync ; 140-151 = short sync
cpi STATUS, 90
brlo empty_line ; 20-89: empty lines
breq start_draw_picture ; 90: draw picture
cpi STATUS, 135
brlo empty_line ; 91-134 = draw empty lines
jmp short_sync ; 135-146 = short sync
; reti is at end of all previous jumps
start_draw_picture:
@ -157,7 +157,7 @@ draw_picture:
ldi XH, high(FRAMEBUFFER)
ldi XL, low(FRAMEBUFFER)
; start 256 picture lines
; start 248 picture lines
ldi LINE_COUNTER, SCREEN_HEIGHT-1 ; line counter
h_picture_loop:
; **** start line sync: 4uS, 96 cycles @ 24Mhz