; CHIBI PC-09 Machine Language Monitor -- BUZBEE
; Copyright (c) 2025 Gale Faraday
; Licensed under MIT

  INCLUDE "bbhash.inc"
  INCLUDE "buzbee.inc"
  INCLUDE "hardware.inc"
  INCLUDE "serial.inc"

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;; BUZBEE Machine Language Monitor for CHIBI PC-09
;;
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  SECTION BUZBEE

  EXPORT BUZBEE

BUZBEE
  bsr NEWLINE ; Setup the new input line and handle display.
  bsr INPLOOP ; Fill input buffer.
  cmpy #$0000 ; No data?
  beq BUZBEE  ;  Try again...
  ; TODO: Parse the input buffer into tokens
  ; TODO: Execute the token buffer
  bra BUZBEE

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;; BUZBEE Input Buffering and Handling Routines
;;
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; Handle new lines; prints a new prompt and then clears the input buffer
NEWLINE
  PZSTR PROMPTLINE  ; Print prompt line
CLRIN               ; Label to just clear input buffer without newline
  clra              ; Init A and X
  ldx #$0000
NEXT@
  sta BBIN_BASE,x   ; Clear input buffer
  leax 1,x
  cmpx #BBIN_DEPTH
  blo NEXT@
  ldy #$0000        ; Reset buffer fill pointer
  rts

; Fills input buffer with characters from the serial console. Sets Y to the
; offset in the input buffer of the last char read.
INPLOOP
  jsr PINCHAR          ; Try to read a char
  cmpd #$0000          ; If no char keep waitin'
  beq INPLOOP
  bitb #UARTF_LSR_DR   ; Is there a char in A?
  beq NOCHAR@
  cmpa #$1B            ; ESC?
  beq HESC@            ;  Handle ESC
  cmpa #$08            ; BS?
  beq HBACKSPC@        ;  Backup a char
  cmpa #$0D            ; CR?
  beq EXIT@            ;  Then parse input buffer
  cmpy #BBIN_DEPTH     ; Are we at the end of the input buffer?
  beq FULLBUF@         ; Handle the buffer being full
ECHO@
  jsr POUTCHAR         ; Echo char back, this includes BS chars
  sta BBIN_BASE,y      ; Add it to the input buffer
  leay 1,y
NOCHAR@
  ; Check for error condition, work based on The Serial Port release 19
  bitb #(UARTF_LSR_FIFO|UARTF_LSR_BI|UARTF_LSR_FE|UARTF_LSR_PE|UARTF_LSR_OE)
  beq INPLOOP
  bitb #UARTF_LSR_OE   ; Check for overrun error
  beq NOOVER@
  PZSTR EM_OVERRUN
NOOVER@
  bitb #UARTF_LSR_PE   ; Check for parity error
  beq NOPARITY@
  PZSTR EM_PARITY
NOPARITY@
  bitb #UARTF_LSR_FE   ; Check for framing error
  beq NOFRAM@
  PZSTR EM_FRAMING
NOFRAM@
  bitb #UARTF_LSR_FIFO ; Check for FIFO error
  beq INPLOOP
  PZSTR EM_FIFO
  bra INPLOOP
EXIT@
  rts
HESC@
  lda #'^              ; Print a char that signifies that ESC was pressed
  jsr POUTCHAR
  ldy #$0000           ; On return we cmpy #$0000 and if eq then newline.
  rts
HBACKSPC@
  clrb                 ; Clear last char
  leay -1,y
  stb BBIN_BASE
  bra ECHO@            ; Echo the char in A
FULLBUF@
  lda #$07             ; ASCII BEL
  jsr POUTCHAR
  bra INPLOOP

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;; BUZBEE Command Hashing Routines
;;
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; Makes a hash of four chars in BBIN starting at offset X.
; @param X: offset in BBIN to read the four chars from
; @return A: resulting hash
MKCMDSUM
  pshs b
  ldb #4           ; Loop over four chars
  clra             ; Initialize accumulator
NEXTC@
  suba BBIN_BASE,x ; Subtract current char from accumulator
  leax 1,x         ; Next char
  decb             ; Reduce count
  cmpb #0          ; Are we at the end?
  bne NEXTC@       ;  No? loop
  rts

; Maps a command hash to a command index, and executes it
; @corrupts B
; @param A: input hash
; @return X: command data table index
CALLFROMHASH
  ldx #0          ; Counting up from zero
NEXTHASH@
  cmpa BBCHT,x    ; Is this hash our hash?
  beq CALCPTR@    ;  Yes? skip to next step to put ptr in x
  leax 1,x        ; Begin considering next hash
  cmpx BBCHTC     ; Is this the last byte?
  blo NEXTHASH@   ;  No? try next hash, Yes? fall through
  PZSTR EM_BADCMD ; Print an error message
  lbra IFHELP     ; Proceed to call "HELP"
CALCPTR@
  tfr x,d         ; Swap into d to do a cheap multiply
  asld            ; Cheaply << to get *2, pointer size
  tfr d,x         ; Restore x from d and jump to function at index
  jmp [BBCMDPTRTBL,x]

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;; BUZBEE Internal Command Functions
;;
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; Print out a help message
IFHELP
  PZSTR HELP_MSG
  rts

; Placeholder function labels to make assembler happy before git commit
IFCALL
IFEXEC
IFPEEK
IFPOKE
IFSREC
  rts

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;; BUZBEE Strings and Tables
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HELP_MSG
  fcc "-- BUZBEE HELP --"
  fcb $0D,$0A
  fcc "Available Commands:"
  fcb $0D,$0A
  fcc "CALL <PTR> - Call the pointer given in <PTR> as a subroutine."
  fcb $0D,$0A
  fcc "EXEC <PTR> - Start program at <PTR>."
  fcb $0D,$0A
  fcc "HELP [CMD] - Display help, command optional."
  fcb $0D,$0A
  fcc "PEEK <BASE> [<HIGH>] - Read memory at <BASE> to <HIGH>."
  fcb $0D,$0A
  fcc "POKE <ADDR> <BYTES> - Overwrite memory with <BYTES> starting at <BASE>."
  fcb $0D,$0A
  fcc "SREC - Enter Motorola S-Record entry mode."
  fcb $00

BBCMDPTRTBL
  fdb IFCALL
  fdb IFEXEC
  fdb IFHELP
  fdb IFPEEK
  fdb IFPOKE
  fdb IFSREC

PROMPTLINE
  fcb $0D,$0A,$25,$00 ; CR LF '%' NUL

EM_OVERRUN
  fcc "!!! Overrun Error !!!"
  fcb $0D,$0A,$00
EM_PARITY
  fcc "!!! Parity Error !!!"
  fcb $0D,$0A,$00
EM_FRAMING
  fcc "!!! Framing Error !!!"
  fcb $0D,$0A,$00
EM_FIFO
  fcc "!!! FIFO Error !!!"
  fcb $0D,$0A,$00
EM_BADCMD
  fcc "!!! Bad Command Hash !!!"
  fcb $0D,$0A,$00