; VIDEO COMPOSITE PAL IO DEVICE ; ; 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... TODO ; ; ELECTRONICALLY: ; The data port PB0 is tied to ground with a 1KOhm resistance. When the MC is busy drawing the screen, the data port is in ; high impedance state, so that avoids causing bus contention, but when read returns a 0bXXXXXXX0 byte. When the MC starts vsync, ; begins checking the port for data... TODO ; ; PINS: ; Video: ; Video pin: PA0 (pin 1) (but all PORTA is used) ; Sync pin: PC0 (pin 22) ; Communication: ; Data port is PORTB [INPUT] ; CLK (clock) signal is on PORTD0 [INPUT] ; RS (register select) on PORTD1 [INPUT] ; BUSY signal is on PORTD2 [OUTPUT] ; Debug: ; Debug hsync single pulse on pin: PC1 (pin 23) (may be disabled) ; .include "m1284def.inc" ; Atmega 1280 device definition ; *** reserved registers *** ; Cursor Position ; POS_COLUMN (0-46) represents the character/chunk column ; POS_ROWP (0-255) represent the chunk row. The caracter row is POS_ROWP/FONT_HEIGHT .def POS_COLUMN = r21 .def POS_ROWP = r20 ; Internal registers .def A = r0 ; accumulator .def STATUS = r25 ; signal status (see STATUS TABLE) ;POS_COARSE = Y ; coarse position (aligned to character column) ;DRAWING_BYTE = X ; current position in framebuffer .def LINE_COUNTER = r23 .def VG_HIGH_ACCUM = r22 ; an accumulator in high registers to be used only by video_generator in interrupt .def HIGH_ACCUM = r16 ; an accumulator in high registers to be used outside of interrupts ; define constant .equ VIDEO_PORT_OUT = PORTA ; Used all PORTA, but connected only PA0 .equ SYNC_PIN = PC0 ; Sync pin (pin 22) .equ DEBUG_PIN = PC1 ; DEBUG: Single vertical sync pulse to trigger oscilloscope (pin 23) .equ DATA_PORT_IN = PINB .equ CLK_PIN = PD0 .equ RS_PIN = PD1 .equ BUSY_PIN = PD2 ; memory .equ FRAMEBUFFER = 0x0100 .equ FRAMEBUFFER_END = 0x2F00 .equ SCREEN_HEIGHT = 248 ; start vector .org 0x0000 rjmp main ; reset vector: jump to main label .org 0x001E rjmp on_tim1_ovf ; interrupt for timer 1 overflow (used by video generation) .org 0x40 ; main program main: ; **** I/O SETUP **** ; pins setup sbi DDRC, SYNC_PIN ; set pin as output sbi DDRC, DEBUG_PIN ; set pin as output sbi DDRC, BUSY_PIN ; set pin as output cbi DDRD, CLK_PIN ; set pin as input ldi HIGH_ACCUM, 0xFF out DDRA, HIGH_ACCUM ; set port as output (contains video pin) ldi HIGH_ACCUM, 0x00 out DDRB, HIGH_ACCUM ; set port as input (used as data bus) ; **** MEMORY SETUP **** ; clear ram ;*** Load data into ram *** Set X to 0x0100 ldi XH, high(FRAMEBUFFER) ldi XL, low(FRAMEBUFFER) load_mem_loop: clr r17 st X+, r17 ; if reached the last framebuffer byte, exit cycle cpi XH, 0b00111110 brne load_mem_loop ; if not 0, repeat h_picture_loop cpi XL, 0b11000000 brne load_mem_loop ; if not 0, repeat h_picture_loop ; **** TIMERS AND DRAWING IMAGE ROUTINES SETUP **** ; 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 HIGH_ACCUM, 0b00000000 sts PRR0, HIGH_ACCUM ; Set timer prescaler to 1:1 LDI HIGH_ACCUM,0b00000001 sts TCCR1B,HIGH_ACCUM ; Enambe timer1 overflow interrupt LDI HIGH_ACCUM,0b00000001 STS TIMSK1,HIGH_ACCUM ; Enable interrupts globally SEI ; Timer setup completed. ; **** MAIN ROUTINE **** ; Wait for data (it never exits) ; jmp comm_init ; draw example image ;call draw_cat ; test draw character routine call cursor_pos_home dctest: ldi r18, 0x41 draw_chars: mov HIGH_ACCUM, r18 call draw_char dc_continue: ; wait ser r19 dc_wait_loop_1: ldi r24, 64 dc_wait_loop_2: dec r24 brne dc_wait_loop_2 dec r19 brne dc_wait_loop_1 inc r18 cpi r18, 0x5B brne draw_chars jmp dctest forever: jmp forever .include "video_generator.asm" ; Asyncronous timer-interrupt-based video generation .include "character_generator.asm" ; Character generator ;.include "communication.asm" ; Communication with Pat80 .include "font.asm" ; Font face .include "example_data/cat.asm" ; Cat image