Subversion Repositories socgen

; minimal monitor for EhBASIC and 6502 simulator V1.05

; To run EhBASIC on the simulator load and assemble [F7] this file, start the simulator
; running [F6] then start the code with the RESET [CTRL][SHIFT]R. Just selecting RUN
; will do nothing, you'll still have to do a reset to run the code.

        .include "basic.asm"

; put the IRQ and MNI code in RAM so that it can be changed

IRQ_vec = VEC_SV+2              ; IRQ code vector
NMI_vec = IRQ_vec+$0A   ; NMI code vector

; setup for the 6502 simulator environment

IO_AREA = $F000         ; set I/O area for this monitor

ACIAsimwr       = IO_AREA+$01   ; simulated ACIA write port
ACIAsimrd       = IO_AREA+$04   ; simulated ACIA read port

; now the code. all this does is set up the vectors and interrupt code
; and wait for the user to select [C]old or [W]arm start. nothing else
; fits in less than 128 bytes

        *=      $FF80                   ; pretend this is in a 1/8K ROM

; reset vector points here

RES_vec
        CLD                             ; clear decimal mode
        LDX     #$FF                    ; empty stack
        TXS                             ; set the stack

; set up vectors and interrupt code, copy them to page 2

        LDY     #END_CODE-LAB_vec       ; set index/count
LAB_stlp
        LDA     LAB_vec-1,Y             ; get byte from interrupt code
        STA     VEC_IN-1,Y              ; save to RAM
        DEY                             ; decrement index/count
        BNE     LAB_stlp                ; loop if more to do

; now do the signon message, Y = $00 here

LAB_signon
        LDA     LAB_mess,Y              ; get byte from sign on message
        BEQ     LAB_nokey               ; exit loop if done

        JSR     V_OUTP          ; output character
        INY                             ; increment index
        BNE     LAB_signon              ; loop, branch always

LAB_nokey
        JSR     V_INPT          ; call scan input device
        BCC     LAB_nokey               ; loop if no key

        AND     #$DF                    ; mask xx0x xxxx, ensure upper case
        CMP     #'W'                    ; compare with [W]arm start
        BEQ     LAB_dowarm              ; branch if [W]arm start

        CMP     #'C'                    ; compare with [C]old start
        BNE     RES_vec         ; loop if not [C]old start

        JMP     LAB_COLD                ; do EhBASIC cold start

LAB_dowarm
        JMP     LAB_WARM                ; do EhBASIC warm start

; byte out to simulated ACIA

ACIAout
        STA     ACIAsimwr               ; save byte to simulated ACIA
        RTS

; byte in from simulated ACIA

ACIAin
        LDA     ACIAsimrd               ; get byte from simulated ACIA
        BEQ     LAB_nobyw               ; branch if no byte waiting

        SEC                             ; flag byte received
        RTS

LAB_nobyw
        CLC                             ; flag no byte received
no_load                         ; empty load vector for EhBASIC
no_save                         ; empty save vector for EhBASIC
        RTS

; vector tables

LAB_vec
        .word   ACIAin          ; byte in from simulated ACIA
        .word   ACIAout         ; byte out to simulated ACIA
        .word   no_load         ; null load vector for EhBASIC
        .word   no_save         ; null save vector for EhBASIC

; EhBASIC IRQ support

IRQ_CODE
        PHA                             ; save A
        LDA     IrqBase         ; get the IRQ flag byte
        LSR                             ; shift the set b7 to b6, and on down ...
        ORA     IrqBase         ; OR the original back in
        STA     IrqBase         ; save the new IRQ flag byte
        PLA                             ; restore A
        RTI

; EhBASIC NMI support

NMI_CODE
        PHA                             ; save A
        LDA     NmiBase         ; get the NMI flag byte
        LSR                             ; shift the set b7 to b6, and on down ...
        ORA     NmiBase         ; OR the original back in
        STA     NmiBase         ; save the new NMI flag byte
        PLA                             ; restore A
        RTI

END_CODE

LAB_mess
        .byte   $0D,$0A,"6502 EhBASIC [C]old/[W]arm ?",$00
                                        ; sign on string

; system vectors

        *=      $FFFA

        .word   NMI_vec         ; NMI vector
        .word   RES_vec         ; RESET vector
        .word   IRQ_vec         ; IRQ vector