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More CRTC tinkering

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This commit is contained in:
Seth Morabito 2014-08-14 21:03:52 -07:00
parent f35fbce38b
commit 70ab2a6fc2
2 changed files with 79 additions and 26 deletions
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4
samples/ehbasic_crtc/basic.asm
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@ -436,8 +436,8 @@ Ibuffs = IRQ_vec+$14
; start of input buffer after IRQ/NMI code
Ibuffe = Ibuffs+$47; end of input buffer
Ram_base = $0300 ; start of user RAM (set as needed, should be page aligned)
Ram_top = $C000 ; end of user RAM+1 (set as needed, should be page aligned)
Ram_base = $0300 ; start of user RAM (set as needed, should be page aligned)
Ram_top = $A000 ; end of user RAM+1 (set as needed, should be page aligned)
; This start can be changed to suit your system

101
samples/ehbasic_crtc/min_mon.asm
View File

@ -21,7 +21,9 @@ ACIAstatus = IO_AREA+1
ACIAcommand = IO_AREA+2
ACIAcontrol = IO_AREA+3
CRSR_L = $20B
CPOS_L = $E0 ; Cursor address (low)
CPOS_H = $E1 ; Cursor address (high)
COUTC = $E2 ; Temp storage for char out.
; now the code. all this does is set up the vectors and interrupt code
@ -38,6 +40,13 @@ RES_vec
LDX #$FF ; empty stack
TXS ; set the stack
;; Initialize the CRTC
LDA #$00 ; Set cursor start to $7000
STA CPOS_L
LDA #$70
STA CPOS_H
; Initialize the ACIA
ACIA_init
LDA #$00
@ -99,26 +108,44 @@ ACIAout:
;;; 2. Scroll if necessary.
;;; 3. Store new cursor position in CRTC.
CRSR_L = $DE ; Cursor address (low)
CRSR_H = $DF ; Cursor address (high)
COL_M = 40 ; Max Column
ROW_M = 25 ; Max Row
CRSR_C = $E0 ; Cursor Column #
CRSR_R = $E1 ; Cursor Row #
CRTCout:
STA COUTC ; Store the character going out
JSR ACIAout ; Also echo to terminal for debugging.
;; 1. Is this an enter (cr/lf)?
;; Set CRSR_C = 0.
;; Is this a CR or LF?
CMP #$0D
BEQ @dolf
CMP #$0A
BEQ @docr
;; Is this a backspace?
CMP #$08
BEQ @dobs
;; Otherwise, this is a normal character
;; Do normal character stuff.
TYA ; Save Y
PHA
LDA COUTC ; Restore character going out
LDY #$00
STA (CPOS_L),Y
INC CPOS_L
PLA ; Restore Y
TAY
JMP @done
@dolf:
;; Handle a LF
;; Increment CRSR_R.
;; If CRSR_R > ROW_M, scroll..
CMP #$0A
BEQ @doenter
CMP #$0D
BEQ @doenter
;; 1. Is this a backspace?
@docr:
;; Handle a CR
;; Set CRSR_C = 0.
@dobs:
;; 2. Is this a backspace?
;; IF CRSR_C == 0 && CRSR_R == 0
;; Do nothing, already home
;; If CRSR_C > 0
@ -126,19 +153,45 @@ CRTCout:
;; Else
;; Set CRSR_C = COL_M
;; Set CRSR_R = CRSR_R - 1
;;
CMP #$08
BEQ @dobs
;;
;; Otherwise, this is a normal character
;; Do normal character stuff.
JMP @done
@doenter:
@dobs:
@done:
;; Now new cursor Column and Row have been calculated,
;; and we know if we need to scroll.
;;
;; (CPOS_H) = $70 + (row /
RTS
;; Convert CRSR_C, CRSR_R into Cursor Address.
;; Result stored in CPOS_L,CPOS_H
;;
;; C_POS:
;; ;; Multiply CRSR_R * $28, store result in CPOS_L,CPOS_H
;; LDA CRSR_R ; Copy CRSR_R to CPOS_L
;; STA CPOS_L
;; LDA #$00
;; LDX #$08
;; LSR CPOS_L
;; @cpos1: BCC @cpos2
;; CLC
;; ADC #$28
;; @cpos2: ROR
;; ROR CPOS_L
;; DEX
;; BNE @cpos1
;; STA CPOS_H
;; ;; At this point, CPOS_L,CPOS_H holds the product
;; ;; of CRSR_R and $28. We need to add CRSR_C with
;; ;; an unsigned 16-bit add.
;; CLC
;; LDA CRSR_C
;; ADC CPOS_L
;; STA CPOS_L
;; BCC @noinc ; If carry wasn't set, no need
;; INC CPOS_H ; to increment CPOS_H
;; @noinc:
;
; byte in from ACIA. This subroutine will also force
; all lowercase letters to be uppercase.