Minicube64 is a fantasy console style emulator based on 6502, with the intention of helping people learn how games were made for older systems such as Atari 2600, NES or C64, but without many of the difficult hardware restrictions.
The introduction page is what I'm annotating below. Hopefully these notes will give more insight into what the assembly is doing in the console.
Writing a New ROM
On the page "Writing a New ROM", there is a test program written in 6502 assembly. I figured a good way to learn what was going on was to annotate the whole thing and really grok it.
This is the contents of
include "64cube.inc" ; Include the helper functinos for 64cube ENUM $0 ; Enumerate the following vars starting at $0000 counter rBYTE 1 ; Set counter to type of byte with value of 1 ENDE ; End enumeration org $200 ; Specify the origin of the ROM program sei ; Set interrupt flag to 1 ldx #$ff ; Load 255 into X txs ; Transfer the contents of x to the stack ; pointer lda #$0 ; Load 0 into A sta VIDEO ; Store A into VIDEO (location $100) _setw IRQ, VBLANK_IRQ ; Store the address of IRQ at VBLANK_IRQ (in the ; include file) cli ; Clear interrupt flag Infinite: ; Set label for 'Infinite' at this address jmp Infinite ; Jump to the 'Infinite' label, effectively ; creating an infinite loop IRQ: ; Set label for 'IRQ' at this address inc counter ; Increment the value at 'counter' rti ; Return to where the interrupt occurred
This is the relevant contents of
... ; NOTE NOTE ; normal 6502 has irq vectors at $fffe ; we have them at $010e NMI_IRQ = $10c VBLANK_IRQ = $10e ... MACRO _setw value,dest ; create a macro named _setw with two params: ; 'value', and 'dest' lda #<value ; load the high byte of value into register 'a' sta dest ; store the value in register 'a' at the address ; of destination lda #>value ; load the low byte of value into register 'a' sta dest+1 ; store the value in register 'a' at the address ; of destination + 1 ENDM ; signify the end of the macro
Working With Pixels
This is the changed contents of the above
... txs ; This will set the video buffer page in a 4k page in memory lda #$f ; Load high byte of page into 'a' ; register sta VIDEO ; Store value in 'a' register at 'VIDEO' ; This will create a pixel of color #64 at pixel address $f820 lda #$64 ; Load decimal value 64 into 'a' ; register ;sta $f820 ; Store value in 'a' register at $f820 sta $f000 + 32 + 32 * 64 ; Same as above but with MATH _setw IRQ, VBLANK_IRQ ...
Basic Drawing Example
This example shows how to set up a custom palette as well as drawing those colors to screen.
include "64cube.inc" ; Include the helper functions ENUM $0 ; Enumerate values starting from $0000 counter rBYTE 1 ; Set 'counter' as 1 byte ENDE ; End enumeration org $200 ; Set program origin to $0200 sei ; Set interrupt disable flag ldx #$ff ; Load value $ff into X txs ; Transfer value of X into the stack ; pointer ; This will set the video buffer page in the $f000 page in memory lda #$f ; Load high byte of page into 'a' ; register sta VIDEO ; Store value in A at 'VIDEO' ; This will set the colors buffer page in the $5000 page in memory lda #$5 ; Load highbyte of page into 'a' ; register sta COLORS ; Store value in A at 'COLORS' _setw IRQ, VBLANK_IRQ ; Set value of VBLANK_IRQ to address of ; 'IRQ' label jsr Draw ; Jump to 'Draw' subroutine cli ; Clear interrupt disable flag Infinite: ; Set 'Infinite' label jmp Infinite ; Create infinite loop IRQ: ; Set 'IRQ' label inc counter ; Increment 'counter' rti ; Return from interrupt Draw: ; Set 'Draw' label ; This will create pixels of colors from the palette below at address ; $f820. The color is found by referencing the colors page at the ; addresses listed below (#1, #2, #3). lda #0 ; Create counter of 0 at A Loop: ; Create Loop label adc #1 ; Increment A tax ; Transfer value of A into X sta $f000 + 32 * 64 + 31,X ; Store X into ; $f000 + 32 * 64 + 31 and X cmp #3 ; Compare x with 3 bne Loop ; If not equal go back to Loop rts ; Else return from subroutine Palette: ; Set 'Palette' label ; This will set the palette of colors available in the COLORS page, ; enumerating from $00 upward within that page. org $0500 ; Set program origin to $0500 hex 000000 ff0000 00ff00 0000ff ; Set these colors in colors page
Video Address Locations
These are assuming the video page is being held in the 4k
Last modified: 202109191717