150 lines
4.0 KiB
NASM
150 lines
4.0 KiB
NASM
; VIDEO COMPOSITE PAL IO DEVICE
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;
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; INTERFACING WITH PAT80:
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; Use PortB as data port. Before writing anything, issue a read (pin RW HIGH) and check the busy pin on the data port.
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; If the busy pin is high, retry reading until goes low. When the busy pin goes low, we have... TODO
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;
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; ELECTRONICALLY:
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; 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
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; high impedance state, so that avoids causing bus contention, but when read returns a 0bXXXXXXX0 byte. When the MC starts vsync,
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; begins checking the port for data... TODO
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;
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; PINS:
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; Video:
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; Video pin: PA0 (pin 1) (but all PORTA is used)
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; Sync pin: PC0 (pin 22)
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; Communication:
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; Data port is PORTB [INPUT]
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; CLK (clock) signal is on PORTD0 [INPUT]
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; RS (register select) on PORTD1 [INPUT]
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; BUSY signal is on PORTD2 [OUTPUT]
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; Debug:
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; Debug hsync single pulse on pin: PC1 (pin 23) (may be disabled)
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;
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.include "m1284def.inc" ; Atmega 1280 device definition
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; *** reserved registers ***
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; Video generator registers:
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; X(R27, R26)
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.def STATUS = r25 ; signal status (see STATUS TABLE)
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.def VG_HIGH_ACCUM = r24 ; an accumulator in high registers to be used only by video_generator in interrupt
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.def LINE_COUNTER = r23
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; Character generator registers:
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.def POS_COLUMN = r22 ; POS_COLUMN (0-46) represents the character/chunk column
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.def POS_ROWP = r21 ; POS_ROWP (0-255) represent the chunk row. The caracter row is POS_ROWP/FONT_HEIGHT
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.def HIGH_ACCUM = r20 ; an accumulator in high registers to be used outside of interrupts
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.def A = r0 ; general purpose accumulator to be used outside of interrupts
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; Hardware pins and ports
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.equ VIDEO_PORT_OUT = PORTA ; Used all PORTA, but connected only PA0
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.equ SYNC_PIN = PC0 ; Sync pin (pin 22)
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.equ DEBUG_PIN = PC1 ; DEBUG: Single vertical sync pulse to trigger oscilloscope (pin 23)
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.equ DATA_PORT_IN = PIND
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.equ CLK_PIN = PC2
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.equ RS_PIN = PC3
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.equ BUSY_PIN = PC4
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; Memory map
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.equ FRAMEBUFFER = 0x0F70
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.equ FRAMEBUFFER_END = 0x3C00
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.equ SCREEN_HEIGHT = 248
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; start vector
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.org 0x0000
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rjmp main ; reset vector: jump to main label
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.org 0x001E
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rjmp on_tim1_ovf ; interrupt for timer 1 overflow (used by video generation)
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.org 0x40
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; main program
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main:
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; **** I/O SETUP ****
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; pins setup
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sbi DDRC, SYNC_PIN ; set pin as output
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sbi DDRC, DEBUG_PIN ; set pin as output
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sbi DDRC, BUSY_PIN ; set pin as output
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cbi DDRD, CLK_PIN ; set pin as input
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ldi HIGH_ACCUM, 0xFF
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out DDRA, HIGH_ACCUM ; set port as output (contains video pin)
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ldi HIGH_ACCUM, 0x00
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out DDRB, HIGH_ACCUM ; set port as input (used as data bus)
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; **** MEMORY SETUP ****
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call clear_screen
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; **** TIMERS AND DRAWING IMAGE ROUTINES SETUP ****
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; Timer setup (use 16-bit counter TC1)
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; The Power Reduction TC1 and TC3 bits in the Power Reduction Registers (PRR0.PRTIM1 and
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; PRR1.PRTIM3) must be written to zero to enable the TC1 and TC3 module.
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ldi HIGH_ACCUM, 0b00000000
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sts PRR0, HIGH_ACCUM
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; Set timer prescaler to 1:1
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LDI HIGH_ACCUM,0b00000001
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sts TCCR1B,HIGH_ACCUM
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; Enambe timer1 overflow interrupt
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LDI HIGH_ACCUM,0b00000001
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STS TIMSK1,HIGH_ACCUM
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; Enable interrupts globally
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SEI
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; Timer setup completed.
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; **** MAIN ROUTINE ****
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; Wait for data (it never exits)
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;jmp comm_init
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; draw example image
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;call draw_cat
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; test draw character routine
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call cursor_pos_home
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dctest:
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ldi r18, 0x41
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draw_chars:
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mov HIGH_ACCUM, r18
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call draw_char
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dc_continue:
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; wait
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ser r19
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dc_wait_loop_1:
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ldi r24, 64
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dc_wait_loop_2:
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dec r24
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brne dc_wait_loop_2
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dec r19
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brne dc_wait_loop_1
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inc r18
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cpi r18, 0x5B
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brne draw_chars
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; call draw_carriage_return
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jmp dctest
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forever:
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jmp forever
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.include "video_generator.asm" ; Asyncronous timer-interrupt-based video generation
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.include "character_generator.asm" ; Character generator
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;.include "communication.asm" ; Communication with Pat80
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.include "font.asm" ; Font face
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;.include "example_data/cat.asm" ; Cat image
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