In this lab, you will continue learning some of the basics of 6502 assembly language, in preparation for learning more complex x86_64 and AArch64 assembly language.
Mob Programming is an extended form of Pair Programming.
Follow these steps:
1. Have the Driver open the 6502 Emulator at http://6502.cdot.systems in another tab or window, keeping this lab open.
Important: The emulator does not save your work automatically. Remember to periodically save it to a file (copy-and-paste the code or use the Save button to create local files). Recommendation: save your files to a directory, and use git to manage that directory.
2. The following code moves a graphic around the screen:
; ; draw-image-subroutine.6502 ; ; This is a routine that can place an arbitrary ; rectangular image on to the screen at given ; coordinates. ; ; Chris Tyler 2024-09-17 ; Licensed under GPLv2+ ; ; ; The subroutine is below starting at the ; label "DRAW:" ; ; Test code for our subroutine ; Moves an image diagonally across the screen ; Zero-page variables define XPOS $20 define YPOS $21 ; Set up the data structure ; The syntax #<LABEL returns the low byte of LABEL ; The syntax #>LABEL returns the high byte of LABEL LDA #<G_X ; POINTER TO GRAPHIC STA $10 LDA #>G_X STA $11 LDA #$05 STA $12 ; IMAGE WIDTH STA $13 ; IMAGE HEIGHT ; Set initial position X=Y=0 LDA #$00 STA XPOS STA YPOS ; Main loop for diagonal animation MAINLOOP: ; Set pointer to the image ; Use G_O or G_X as desired LDA #<G_O STA $10 LDA #>G_O STA $11 ; Place the image on the screen LDA #$10 ; Address in zeropage of the data structure LDX XPOS ; X position LDY YPOS ; Y position JSR DRAW ; Call the subroutine ; Delay to show the image LDY #$00 LDX #$50 DELAY: DEY BNE DELAY DEX BNE DELAY ; Set pointer to the blank graphic LDA #<G_BLANK STA $10 LDA #>G_BLANK STA $11 ; Draw the blank graphic to clear the old image LDA #$10 ; LOCATION OF DATA STRUCTURE LDX XPOS LDY YPOS JSR DRAW ; Increment the position INC XPOS INC YPOS ; Continue for 29 frames of animation LDA #28 CMP XPOS BNE MAINLOOP ; Repeat infinitely JMP $0600 ; ========================================== ; ; DRAW :: Subroutine to draw an image on ; the bitmapped display ; ; Entry conditions: ; A - location in zero page of: ; a pointer to the image (2 bytes) ; followed by the image width (1 byte) ; followed by the image height (1 byte) ; X - horizontal location to put the image ; Y - vertical location to put the image ; ; Exit conditions: ; All registers are undefined ; ; Zero-page memory locations define IMGPTR $A0 define IMGPTRH $A1 define IMGWIDTH $A2 define IMGHEIGHT $A3 define SCRPTR $A4 define SCRPTRH $A5 define SCRX $A6 define SCRY $A7 DRAW: ; SAVE THE X AND Y REG VALUES STY SCRY STX SCRX ; GET THE DATA STRUCTURE TAY LDA $0000,Y STA IMGPTR LDA $0001,Y STA IMGPTRH LDA $0002,Y STA IMGWIDTH LDA $0003,Y STA IMGHEIGHT ; CALCULATE THE START OF THE IMAGE ON ; SCREEN AND PLACE IN SCRPTRH ; ; THIS IS $0200 (START OF SCREEN) + ; SCRX + SCRY * 32 ; ; WE'LL DO THE MULTIPLICATION FIRST ; START BY PLACING SCRY INTO SCRPTR LDA #$00 STA SCRPTRH LDA SCRY STA SCRPTR ; NOW DO 5 LEFT SHIFTS TO MULTIPLY BY 32 LDY #$05 ; NUMBER OF SHIFTS MULT: ASL SCRPTR ; PERFORM 16-BIT LEFT SHIFT ROL SCRPTRH DEY BNE MULT ; NOW ADD THE X VALUE LDA SCRX CLC ADC SCRPTR STA SCRPTR LDA #$00 ADC SCRPTRH STA SCRPTRH ; NOW ADD THE SCREEN BASE ADDRESS OF $0200 ; SINCE THE LOW BYTE IS $00 WE CAN IGNORE IT LDA #$02 CLC ADC SCRPTRH STA SCRPTRH ; NOTE WE COULD HAVE DONE TWO: INC SCRPTRH ; NOW WE HAVE A POINTER TO THE IMAGE IN MEM ; COPY A ROW OF IMAGE DATA COPYROW: LDY #$00 ROWLOOP: LDA (IMGPTR),Y STA (SCRPTR),Y INY CPY IMGWIDTH BNE ROWLOOP ; NOW WE NEED TO ADVANCE TO THE NEXT ROW ; ADD IMGWIDTH TO THE IMGPTR LDA IMGWIDTH CLC ADC IMGPTR STA IMGPTR LDA #$00 ADC IMGPTRH STA IMGPTRH ; ADD 32 TO THE SCRPTR LDA #32 CLC ADC SCRPTR STA SCRPTR LDA #$00 ADC SCRPTRH STA SCRPTRH ; DECREMENT THE LINE COUNT AND SEE IF WE'RE ; DONE DEC IMGHEIGHT BNE COPYROW RTS ; ========================================== ; 5x5 pixel images ; Image of a blue "O" on black background G_O: DCB $00,$0e,$0e,$0e,$00 DCB $0e,$00,$00,$00,$0e DCB $0e,$00,$00,$00,$0e DCB $0e,$00,$00,$00,$0e DCB $00,$0e,$0e,$0e,$00 ; Image of a yellow "X" on a black background G_X: DCB $07,$00,$00,$00,$07 DCB $00,$07,$00,$07,$00 DCB $00,$00,$07,$00,$00 DCB $00,$07,$00,$07,$00 DCB $07,$00,$00,$00,$07 ; Image of a black square G_BLANK: DCB $00,$00,$00,$00,$00 DCB $00,$00,$00,$00,$00 DCB $00,$00,$00,$00,$00 DCB $00,$00,$00,$00,$00 DCB $00,$00,$00,$00,$00
3. Test the code by pressing the Assemble button, then the Run button. If the there are any errors assembling (compiling) the code, they will appear in the message area at the bottom of the page. Make sure the code is running correctly and that you understands how it works. Don't be afraid to experiment!
4. Select a starting location for the graphic where X and Y have different values.
5. Select an X increment that is -1 or +1, and a Y increment that is -1 or +1.
6. Successively move the graphic by adding the X and Y increments to the graphic's X and Y position.
7. Make the graphic bounce when it hits the edge of the bitmapped screen, both vertically (when it hits the top/bottom) and vertically (when it hits the left/right edge).
========== This is the end of the in-class portion of the lab. ==========
Continue the remaining portion of the lab on your own.
Try these experiments: - Permit values other than -1 and +1 for the X and Y increments. - Permit fractional values for the X and Y increments (e.g., +1.5 or -0.75) - Change the graphic each time it bounces.
Post an entry on your blog describing your experiments in this lab. Follow the Blog Guidelines. Include code as text (and not screenshots), but feel free to include screenshots of the bitmapped display.
Include in your blog post:
Remember that labs are marked on a scale of 0-3:
Remember to follow the Blog Guidelines as you write.
The labs in SPO600 do not have specific due dates, but:
Therefore it is strongly recommended that you keep up with the labs. If you have partially or mostly completed the lab, write a blog post about what you've done, and you can supplement this with an additional blog post at a late date when you complete the lab – multiple blog posts about one lab are completely acceptable.