mirror of
https://github.com/sethm/symon.git
synced 2024-06-08 11:00:42 +00:00
450 lines
8.3 KiB
NASM
450 lines
8.3 KiB
NASM
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; minimal monitor for EhBASIC and 6502 simulator V1.05
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; To run EhBASIC on the simulator load and assemble [F7] this file, start the simulator
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; running [F6] then start the code with the RESET [CTRL][SHIFT]R. Just selecting RUN
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; will do nothing, you'll still have to do a reset to run the code.
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.feature labels_without_colons
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.include "basic.asm"
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; put the IRQ and MNI code in RAM so that it can be changed
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IRQ_vec = VEC_SV+2 ; IRQ code vector
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NMI_vec = IRQ_vec+$0A ; NMI code vector
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; setup for the 6502 simulator environment
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IO_AREA = $8800
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ACIAdata = IO_AREA ; simulated ACIA r/w port
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ACIAstatus = IO_AREA+1
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ACIAcommand = IO_AREA+2
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ACIAcontrol = IO_AREA+3
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CRTC_A = $9000 ; CRTC register select
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CRTC_C = $9001 ; CRTC register IO
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CADDR_L = $E0 ; Cursor address (low)
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CADDR_H = $E1 ; Cursor address (high)
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C_COL = $E2 ; Cursor column
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C_ROW = $E3 ; Cursor row
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COUTC = $E4 ; Temp storage for char out.
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R_STRT = $E5 ; E5,E6 contains starting address of
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; current row
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R_NXT = $E7 ; E7,E8 contains starting address of
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; next row
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N_ROWS = 24
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N_COLS = 40
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; now the code. all this does is set up the vectors and interrupt code
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; and wait for the user to select [C]old or [W]arm start. nothing else
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; fits in less than 128 bytes
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.segment "MONITOR"
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.org $FC00 ; pretend this is in a 1/8K ROM
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; reset vector points here
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RES_vec:
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CLD ; clear decimal mode
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LDX #$FF ; empty stack
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TXS ; set the stack
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;; Initialize the CRTC
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LDA #$01
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STA CRTC_A
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LDA #N_COLS ; 40 columns
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STA CRTC_C
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LDA #$06
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STA CRTC_A
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LDA #N_ROWS ; 24 rows
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STA CRTC_C
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LDA #$70
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STA CADDR_H
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LDA #$00
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STA CADDR_L
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STA C_ROW
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STA C_COL
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JSR CLRVID
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;; TODO: Initialize params on CRTC
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; Initialize the ACIA
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ACIA_init:
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LDA #$00
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STA ACIAstatus ; Soft reset
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LDA #$0B
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STA ACIAcommand ; Parity disabled, IRQ disabled
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LDA #$1E
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STA ACIAcontrol ; Set output for 8-N-1 9600
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; set up vectors and interrupt code, copy them to page 2
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LDY #END_CODE-LAB_vec ; set index/count
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LAB_stlp:
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LDA LAB_vec-1,Y ; get byte from interrupt code
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STA VEC_IN-1,Y ; save to RAM
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DEY ; decrement index/count
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BNE LAB_stlp ; loop if more to do
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; now do the signon message, Y = $00 here
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LAB_signon:
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LDA LAB_mess,Y ; get byte from sign on message
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BEQ LAB_nokey ; exit loop if done
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JSR V_OUTP ; output character
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INY ; increment index
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BNE LAB_signon ; loop, branch always
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LAB_nokey:
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JSR V_INPT ; call scan input device
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BCC LAB_nokey ; loop if no key
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AND #$DF ; mask xx0x xxxx, ensure upper case
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CMP #'W' ; compare with [W]arm start
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BEQ LAB_dowarm ; branch if [W]arm start
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CMP #'C' ; compare with [C]old start
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BNE RES_vec ; loop if not [C]old start
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JMP LAB_COLD ; do EhBASIC cold start
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LAB_dowarm:
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JMP LAB_WARM ; do EhBASIC warm start
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ACIAout:
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PHA
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@loop: LDA ACIAstatus
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AND #$10
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BEQ @loop ; Wait for buffer to empty
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PLA
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STA ACIAdata
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RTS
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;;; Byte out to the CRTC
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;;;
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;;; 1. Increment cursor position.
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;;; 2. Scroll if necessary.
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;;; 3. Store new cursor position in CRTC.
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CRTCout:
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JSR ACIAout ; Also echo to terminal for debugging.
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;; In parallel, we're maintaining two states:
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;; - The address of the cursor, and
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;; - The Column/Row of the cursor.
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;;
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;; The latter state is used to handle scrolling and
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;; for knowing how far to back up the cursor
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;; for a carriage-return.
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;; Backspace
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CMP #$08
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BEQ DO_BS
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;; Line Feed
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CMP #$0a
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BEQ DO_LF
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;; Carriage Return
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CMP #$0d
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BEQ DO_CR
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;; Any other character...
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STA COUTC ; Store the character going out
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JSR COUT1 ; Output it where the cursor is.
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;; We might need to scroll...
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LDA C_ROW
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CMP #N_ROWS-1
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BNE @noscr
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LDA C_COL
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CMP #N_COLS-1
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BNE @noscr
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;; ... yup, we DO need to scroll.
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JSR DO_SCROLL
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RTS
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@noscr: JSR INC_CADDR
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INC C_COL
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JSR SET_CURSOR
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RTS
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;; Handle a back-space character.
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DO_BS: LDA C_COL
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BNE @l1 ; Skip next bit
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LDA #N_COLS-1
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STA C_COL
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BNE @l2
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@l1: DEC C_COL
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@l2: JSR DEC_CADDR ; Back up
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JSR SET_CURSOR
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@l3: LDA #$20
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STA COUTC ; Echo a space ($20)
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JSR COUT1
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RTS
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DO_LF: RTS ; Just swallow LF. CR emulates it.
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DO_CR: SEC
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LDA CADDR_L ; 1. Carriage return to start of row.
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SBC C_COL
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STA CADDR_L
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LDA CADDR_H
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SBC #$00 ; Will decrement H if carry was left
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; set.
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STA CADDR_H
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;; 1. Are we on the last row? Scroll.
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LDA C_ROW
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CMP #N_ROWS-1
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BNE @inc
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JSR DO_SCROLL
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RTS
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@inc: JSR INCROW
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@lf: CLC
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LDA CADDR_L
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ADC #$28 ; Now add $28
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STA CADDR_L
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LDA CADDR_H
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ADC #$00 ; Will increment if carry was set
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STA CADDR_H
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LDA #$00 ; Reset cursor row to 0
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STA C_COL
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JSR SET_CURSOR
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RTS
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SET_CURSOR:
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LDA #14
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STA CRTC_A
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LDA CADDR_H
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STA CRTC_C
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LDA #15
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STA CRTC_A
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LDA CADDR_L
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STA CRTC_C
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RTS
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;; Increment C_ROW and put new
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;; line start address in R_STRT,R_STRT+1
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INCROW: TYA
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PHA
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INC C_ROW
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BNE DECR2 ; Share code with DECROW
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;; Decrement C_ROW and put new
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;; line start address in R_STRT,R_STRT+1
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DECROW: TYA
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PHA
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DEC C_ROW
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DECR2: JSR SETRSTRT
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PLA
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TAY
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RTS
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;; Send the cursor home to the start of the line
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HOME:
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LDY C_ROW
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LDA CRA_LO,Y
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STA CADDR_L
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LDA CRA_HI,Y
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STA CADDR_H
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LDA #$00
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STA C_COL
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RTS
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;; Set the start address of the current row
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SETRSTRT:
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LDY C_ROW
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LDA CRA_LO,Y
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STA R_STRT
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LDA CRA_HI,Y
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STA R_STRT+1
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RTS
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;; Clear the current video line
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CLRLN: LDA #$20
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LDY #$00
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@l1: STA (R_STRT),Y
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INY
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CPY #N_COLS
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BNE @l1
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RTS
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;; Clear the video window and put the cursor at the home
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;; position
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CLRVID:
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LDA #$20
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LDX #N_ROWS-1
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@l1: STX C_ROW
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JSR SETRSTRT
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JSR CLRLN
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DEX
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BPL @l1
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RTS
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;; Handle a scroll request.
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;;
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;; The cursor could be anywhere on the line when this scroll
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;; request comes in.
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DO_SCROLL:
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PHA
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TYA
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PHA
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TXA
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PHA
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;; The idea here is to copy each line to the line above it
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LDX #$00
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@l1: LDA CRA_LO,X
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STA R_STRT
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LDA CRA_HI,X
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STA R_STRT+1
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INX
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LDA CRA_LO,X
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STA R_NXT
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LDA CRA_HI,X
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STA R_NXT+1
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LDY #0
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@l2: LDA (R_NXT),Y
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STA (R_STRT),Y
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INY
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CPY #N_COLS
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BNE @l2
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CPX #N_ROWS
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BNE @l1
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;; Clear the line the cursor occupies.
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JSR CLRLN
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;; Move the cursor to the beginning of the line
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JSR HOME
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JSR SET_CURSOR
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PLA
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TAX
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PLA
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TAY ; Restore Y
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PLA
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RTS
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;; Decrement the cursor address
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INC_CADDR:
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INC CADDR_L
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BNE @l1 ; Did we increment to 0?
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INC CADDR_H ; Yes, also increment high
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@l1: RTS
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;; Increment the cursor address
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DEC_CADDR:
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CMP CADDR_L ; Is low alrady 0?
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BNE @l1
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DEC CADDR_H ; Yes, decrement high
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@l1: DEC CADDR_L
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RTS
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COUT1:
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TYA
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PHA ; Save Y
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LDY #$00
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LDA COUTC
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STA (CADDR_L),Y
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PLA
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TAY ; Restore Y
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RTS
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;;;
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;;; byte in from ACIA. This subroutine will also force
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;;; all lowercase letters to be uppercase, because EhBASIC
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;;; only understands upper-case tokens
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;;;
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ACIAin:
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LDA ACIAstatus ; Read 6551 status
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AND #$08 ;
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BEQ LAB_nobyw ; If rx buffer empty, no byte
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LDA ACIAdata ; Read byte from 6551
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CMP #'a' ; Is it < 'a'?
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BCC @done ; Yes, we're done
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CMP #'{' ; Is it >= '{'?
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BCS @done ; Yes, we're done
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AND #$5f ; Otherwise, mask to uppercase
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@done:
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SEC ; Flag byte received
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RTS
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LAB_nobyw:
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CLC ; flag no byte received
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no_load: ; empty load vector for EhBASIC
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no_save: ; empty save vector for EhBASIC
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RTS
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; vector tables
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LAB_vec:
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.word ACIAin ; byte in from simulated ACIA
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.word CRTCout ; byte out to simulated ACIA
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.word no_load ; null load vector for EhBASIC
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.word no_save ; null save vector for EhBASIC
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; EhBASIC IRQ support
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IRQ_CODE:
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PHA ; save A
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LDA IrqBase ; get the IRQ flag byte
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LSR ; shift the set b7 to b6, and on down ...
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ORA IrqBase ; OR the original back in
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STA IrqBase ; save the new IRQ flag byte
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PLA ; restore A
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RTI
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; EhBASIC NMI support
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NMI_CODE:
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PHA ; save A
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LDA NmiBase ; get the NMI flag byte
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LSR ; shift the set b7 to b6, and on down ...
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ORA NmiBase ; OR the original back in
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STA NmiBase ; save the new NMI flag byte
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PLA ; restore A
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RTI
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END_CODE:
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;;; CRTC row addresses: HIGH
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CRA_HI:
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.byte $70,$70,$70,$70,$70,$70,$70,$71
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.byte $71,$71,$71,$71,$71,$72,$72,$72
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.byte $72,$72,$72,$72,$73,$73,$73,$73
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;;; CRTC row addresses: LOW
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CRA_LO:
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.byte $00,$28,$50,$78,$A0,$C8,$F0,$18
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.byte $40,$68,$90,$B8,$E0,$08,$30,$58
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.byte $80,$A8,$D0,$F8,$20,$48,$70,$98
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; sign on string
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LAB_mess:
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.byte $0D,$0A,"SYMON (C) 2008-2014, SETH MORABITO"
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.byte $0D,$0A,"ENHANCED 6502 BASIC 2.22 (C) LEE DAVISON"
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.byte $0D,$0A,"[C]OLD/[W]ARM ?",$00
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; system vectors
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.segment "VECTORS"
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.org $FFFA
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.word NMI_vec ; NMI vector
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.word RES_vec ; RESET vector
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.word IRQ_vec ; IRQ vector
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