Skip to content

Instantly share code, notes, and snippets.

@pjgpetecodes pjgpetecodes/sprite1_2.asm
Last active Nov 10, 2017

Embed
What would you like to do?
Learn more about clone URLs
Download ZIP
Sam Coupe Sprite Tutorial - Part 2 - Stack Pointer Resolution
Raw
sprite1_2.asm
;
; -----------------------------------------------------------------------------------
; | |
; | Program: SAM Coupe Sprites Tutorial 1 - Part 2 |
; | Filename: Sprites1_2.asm |
; | Version: 1.2 |
; | Date: 12/10/2017 |
; | Author: Pete Gallagher - PJG Creations Ltd |
; | |
; -----------------------------------------------------------------------------------
;
autoexec ; Automatically Execute the Program
ORG 0x8000 ; Store the program in User Address Space
DUMP 1,0 ; Store the Program in Page 1 (B)
;
; ***********************************************************************************
; * *
; * Equates *
; * *
; ***********************************************************************************
;
LMPR: EQU 250 ; The Lower Memory Page Register Address
HMPR: EQU 251 ; The Higher Memory Page Register Address
VMPR: EQU 252 ; The Video Memory Page Register Address
JCLSBL: EQU 334 ; The Clear Screen Routine...
; ... Set A to 0 to clear the whole screen) (0x14E)
JREADKEY: EQU 361 ; The Keyboard Read Routine...
; ... Returns with Z Flag set if no key pressed...
; ... Otherwise A = Keycode for key pressed
;
; ***********************************************************************************
; * *
; * Application Start *
; * *
; ***********************************************************************************
;
DI ; Disable Interupts
;
; Becuase the Stack Pointer lives in Page B, but we're paging the Screen into Pages A and B,
; we need to make sure we save the current Stack Pointer location, and create our own location.
; We rewrite our program here effectively, by storing it's original location in a holding position.
;
LD (System_SP+1),SP; Get the Current Stack Pointer Location and Overwrite...
; ... the holding value below.
;
; Get the Current Screen Page and set the LMPR register up so we can write to the screen
;
IN A,(VMPR) ; Get the VMPR Register, which holds info about...
; ... which Page the Screen is Paged Into
AND 0b00011110 ; We're only interested in the Screen Page...
; ... so mask off everything but the Page Bits...
; ... The result will be stored in the A Register
OR 0b00100000 ; Set Bit 5 which, when loaded into the LMPR register...
; ... will Set the RAM in Page 0
LD (Scr_Page+1),A ; Overwrite the holding value for the Screen Page location...
; ... now that we know it
;
CALL Clear_Screen ; Clear the Screen
;
LD SP,0xC000 ; Set the Stack Pointer to a location of our choosing
;
LD A,(Scr_Page+1) ; Get the current Screen Location which we stored earlier
;
OUT (LMPR),A ;
;
; All of the above shifting around of the Stack Pointer, allows us to Call routines...
; ... Which of course will store their return location on the Stack Pointer...
; ... This would've overwritten some of the Screen Page if left unreseolved...
;
CALL Wait_For_Key ; Wait for a keypress
;
; Print a sprite in the top left corner
;
LD HL,0x0000 ; Point to the Top Left corner of our screen
LD (HL),0xFF ; Set the colour of pixels 0,0 and 0,1 to White
CALL Wait_For_Key ; Wait for a keypress
LD HL,0x0080 ;
LD (HL),0x44 ; Set the colour of pixels 1,0 and 1,1 to Green
CALL Wait_For_Key ; Wait for a keypress
LD HL,0x0001 ;
LD (HL),0xFF ; Set the colour of pixels 0,2 and 0,3 to White
CALL Wait_For_Key ; Wait for a keypress
LD HL,0x0081 ;
LD (HL),0x44 ; Set the colour of pixels 1,2 and 1,3 to Green
CALL Wait_For_Key ; Wait for a keypress
LD HL,0x0100 ;
LD (HL),0xFF ; Set the colour of pixels 1,0 and 1,1 to White
CALL Wait_For_Key ; Wait for a keypress
LD HL,0x0180 ;
LD (HL),0x44 ; Set the colour of pixels 2,0 and 2,1 to Green
CALL Wait_For_Key ; Wait for a keypress
LD HL,0x0101 ;
LD (HL),0xFF ; Set the colour of pixels 1,2 and 1,3 to White
CALL Wait_For_Key ; Wait for a keypress
LD HL,0x0181 ;
LD (HL),0x44 ; Set the colour of pixels 2,2 and 2,3 to Green
CALL Wait_For_Key ; Wait for a keypress
;
; We must remember to switch BASIC back into Page 0
;
LD A,0x1F ; Set ROM0 back into Page A...
OUT (LMPR), A ; ... So that when we try to return to BASIC it all still works!
;
; Return the System Stack Pointer to it's original location in Bank B somewhere...
;
System_SP: LD SP,0 ; Place holder for the System Stack Location...
; This will be overwritten above once we know it's location
EI ; Enable Interupts
;
; Return back to BASIC
;
RET ;
;
; ***********************************************************************************
; * *
; * Clear the Screen *
; * *
; ***********************************************************************************
;
Clear_Screen: XOR A ; Clear the A register, so when passed into clear screen...
; ...it clears the whole screen
CALL JCLSBL ; Clear the Screen
DI ; Disable Interupts
RET ;
;
; ***********************************************************************************
; * *
; * Wait for a KeyPres *
; * *
; ***********************************************************************************
;
Wait_For_Key: LD A,0x1F ; Set for ROM in Page A
OUT (LMPR),A ;
;
Key_Loop: CALL JREADKEY ; Read the Keyboard (Zero if no key)
JR Z,Key_Loop ; If no key pressed, then loop
;
No_Key_Loop: CALL JREADKEY ; Read the Keyboard (Zero if no key)
JR NZ,No_Key_Loop ; If key still pressed, then loop
;
DI ; Disable Interuprts
;
Scr_Page: LD A,0 ; Place holder for the Screen Page...
; ...The 0 will be overwritten above once we know where it is...
OUT (LMPR),A ; Page the Screen into the relevant Page
RET ;
@pjgpetecodes

This comment has been minimized.

Sign in to view
Copy link
Owner Author

pjgpetecodes commented Oct 12, 2017

This is an updated version of https://gist.github.com/PGallagher69/5f30d3e27574e5847027e39c7c5d878d, which caused the Screen to display coloured blocks.

This was because the Stack Pointer was overwriting the Paged in Screen Memory.
Sign up for free to join this conversation on GitHub. Already have an account? Sign in to comment
You can’t perform that action at this time.