pato-z80-home-computer/assembly/bios/monitor.asm

; Pat80 Memory Monitor
; @author Daniele Verducci
;
; Monitor commands (CMD $arg):
;   H (HELP) Shows available commands
;   D (DUMP) $pos Dumps bytes of memory starting at $pos
;   S (SET) $pos $val Replaces byte at $pos with $val
;   L (LOAD) $pos $val
;   R (RUN) $pos Starts executing code from $pos
;   A (ADB) Enters in Assembly Depoy Bridge mode: loads all the incoming bytes in application memory and starts executing.
; The commands are entered with a single letter and the program completes the command

include 'libs/strings.asm'

; CONSTANTS
MON_WELCOME: DB 10,"PAT80 MEMORY MONITOR 0.2",10,0
MON_COMMAND_HELP: DB "HELP",0  ; null terminated strings
MON_COMMAND_DUMP: DB "DUMP",0
MON_COMMAND_SET: DB "SET",0
MON_COMMAND_LOAD: DB "LOAD",0
MON_COMMAND_RUN: DB "RUN",0
MON_COMMAND_ADB: DB "ADB",0
MON_ARG_HEX: DB "    0x",0
MON_HELP: DB 10,"Available commands:\nHELP prints this message\nDUMP [ADDR] shows memory content\nSET [ADDR] sets memory content\nLOAD\nRUN [ADDR] executes code starting from ADDR\nADB starts Assembly Deploy Bridge",0
MON_MSG_ADB: DB 10,"Waiting for data.",0
MON_ERR_SYNTAX: DB "    Syntax error",0
;MON_ADB_TIMEOUT: EQU 0xFF     // Number of cycles after an ADB binary transfer is considered completed
MON_DUMP_BYTES_LINES: EQU 8
MON_DUMP_BYTES_PER_LINE: EQU 8

Monitor_main:
    ; Print welcome string
    ld bc, MON_WELCOME
    call Print
    monitor_main_loop:
        ; Newline
        ld a, 10
        call Printc
        ; Draw prompt char
        ld a, 62 ; >
        call Printc
        ; Read char from command line
        call Readc     ; blocking: returns when a character was read and placed in A reg
        call Strings_charToUpper    ; user may enter lowercase char: transform to upper
        call Printc     ; Print back the character to provide user feedback
        ; Switch case
        ld hl, MON_COMMAND_HELP
        cp (hl)  ; check incoming char is equal to command's first char
        jp z, monitor_help
        ld hl, MON_COMMAND_DUMP
        cp (hl)
        jp z, monitor_dump
        ld hl, MON_COMMAND_SET
        cp (hl)
        jp z, monitor_set
        ld hl, MON_COMMAND_LOAD
        cp (hl)
        jp z, monitor_load
        ld hl, MON_COMMAND_RUN
        cp (hl)
        jp z, monitor_run
        ld hl, MON_COMMAND_ADB
        cp (hl)
        jp z, monitor_adb
        ; Unrecognized command: print error and beep
        ld bc, MON_ERR_SYNTAX
        call Print
        call Beep
    jp monitor_main_loop

monitor_help:
    ld bc, MON_COMMAND_HELP + 1 ; autocomplete command
    call Print

    ld bc, MON_HELP
    call Print
    jp monitor_main_loop

; Asks the user for a memory position and shows the following 64 bytes of memory
; @uses a, b, c, d, e, h, l
monitor_dump:
    ld bc, MON_COMMAND_DUMP + 1 ; autocomplete command
    call Print
    ; Now read the address from the user
    call monitor_arg_2byte  ; returns the read bytes in hl
    ld a, 10 ; newline
    call Printc
    ; now start displaying bytes from memory
    ld e, MON_DUMP_BYTES_LINES    ; the number of lines to display
    monitor_dump_show_bytes_loop:
        ld d, MON_DUMP_BYTES_PER_LINE*2   ; the number of bytes per line to display (*2 as we display two times the same byte: once hex and once ascii)
        ; Print current address
        ld a, h
        call monitor_printHexByte
        ld a, l
        call monitor_printHexByte
        ; print four spaces
        ld a, 32
        call Printc
        call Printc
        call Printc
        call Printc
        monitor_dump_show_bytes_line_loop:  ; counts down from 15 to 0
            ld a, d
            sub MON_DUMP_BYTES_PER_LINE + 1
            jp m, monitor_dump_show_bytes_line_loop_ascii   ; jp if
                ; if position is 8 to 15, print hex value at mem position
                ld a, (hl)
                ; print hex byte
                call monitor_printHexByte
                ; print space
                ld a, 32
                call Printc
                ; if position is 4, print a second space (to group nibbles)
                ld a, d
                cp MON_DUMP_BYTES_PER_LINE / 2 + MON_DUMP_BYTES_PER_LINE + 1
                jp nz, no_second_space
                    ; print second space
                    ld a, 32
                    call Printc
                no_second_space:
                ; move to next mem position
                inc hl
                ; decrement "nth byte on the line" counter
                dec d
                jp monitor_dump_show_bytes_line_loop
            ; if position is 0 to 7, print ascii
            monitor_dump_show_bytes_line_loop_ascii:
                ; is this the first ascii char printed in this line?
                ld a, d
                cp MON_DUMP_BYTES_PER_LINE
                jp nz, no_mempos_decr   ; no need to decrement, already done
                    ; do this only once: printing hex values we advanced the counter by 8 positions. Bring it back.
                    ld bc, MON_DUMP_BYTES_PER_LINE
                    sbc hl, bc
                    ; print 3 spaces to separate hex from ascii
                    ld a, 32
                    call Printc
                    call Printc
                    call Printc
                no_mempos_decr:
                ; print ascii
                ld a, (hl)
                call monitor_printAsciiByte
                ; print space
                ld a, 32
                call Printc
                ; if position is 12 (8+4), print a second space (to group nibbles)
                ld a, d
                cp MON_DUMP_BYTES_PER_LINE / 2 + 1
                jp nz, no_second_space2
                    ; print second space
                    ld a, 32
                    call Printc
                no_second_space2:
                ; move to next mem position
                inc hl
                ; decrement counter: if non zero continue loop
                dec d
                jp nz, monitor_dump_show_bytes_line_loop
        ; print newline
        ld a, 10
        call Printc
        ; decrement line counter
        dec e
        jp nz, monitor_dump_show_bytes_loop ; if line counter is not 0, print another line
    ; if line counter 0, finished
    jp monitor_main_loop

monitor_set:
    ld bc, MON_COMMAND_SET + 1 ; autocomplete command
    call Print
	; Now read the memory address to be changed from the user
    call monitor_arg_2byte  ; returns the read bytes in hl
    ld a, 10 ; newline
    call Printc
	; Start looping memory addresses
	monitor_set_byte_loop:
		; Print current address
        ld a, h
        call monitor_printHexByte
        ld a, l
        call monitor_printHexByte
        ; print two spaces
        ld a, 32
        call Printc
        call Printc
		; print previous memory content (hex)
		ld a, (hl)
		call monitor_printHexByte
		; print space
		ld a, 32
		; print previous memory content (ascii)
		ld a, (hl)
		call monitor_printAsciiByte
		; print space
		ld a, 32
        call Printc
		; ask the user the new memory content
		call monitor_arg_byte	; returns the read byte in a
		ld (hl), a ; write new byte to memory
		inc hl ; next memory position
    ; loops forever: the user can exit canceling a byte insertion (monitor_arg_byte)
	;jp monitor_set_byte_loop
	jp monitor_main_loop

monitor_load:
    ld bc, MON_COMMAND_LOAD + 1 ; autocomplete command
    call Print
    jp monitor_main_loop

monitor_run:
    ld bc, MON_COMMAND_RUN + 1 ; autocomplete command
    call Print
    ; Now read the memory address to be changed from the user
    call monitor_arg_2byte  ; returns the read bytes in hl
    ld a, 10 ; newline
    call Printc
    jp (hl)    ; Start executing code

monitor_adb:
    ld bc, MON_COMMAND_ADB + 1 ; autocomplete command
    call Print
    ; start copying incoming data to application space
    call monitor_copyTermToAppMem
    ;jp APP_SPACE    ; Start executing code
    ld bc, APP_SPACE
    call Print
    jp monitor_main_loop

; Prints "0x" and read 1 hex byte (2 hex digits, e.g. 0x8C)
; @return a the read byte
; @uses a, b, c
monitor_arg_byte:
    ; Print 0x... prompt
    ld bc, MON_ARG_HEX
    call Print
    ; Read 2 digits
    call monitor_arg_byte_impl
    ret

; Prints "0x" and reads 2 hex bytes (4 hex digits e.g. 0x3F09)
; @return hl the two read bytes
; @uses a, b, c, h, l
monitor_arg_2byte:
    ; Print 0x... prompt
    ld bc, MON_ARG_HEX
    call Print
    ; Read 2 digits
    call monitor_arg_byte_impl
    ld h, a ; move result to h
    ; Read 2 digits
    call monitor_arg_byte_impl
    ld l, a ; move result to l
    ret

; Read 2 hex digits
; @return a the read byte
; @uses a, b, c
monitor_arg_byte_impl:
    ; Receive first hex digit
    call monitor_readHexDigit
    ; First hex digit is the most signif nibble, so rotate left by 4 bits
    rlca a
    rlca a
    rlca a
    rlca a
    ; the lower nibble must now be discarded
    and %11110000
    ld c, a     ; save shifted nibble in c
    ; Read second hex digit
    call monitor_readHexDigit
    ; Join the two nibbles in a single byte: second digit is already in a,
    ; so we OR with the previously shifted c and obtain the complete byte in a.
    or c
    ret

; Reads an hex digit (0 to 9, A to F)
; @return a the read nibble
; @uses a, b
monitor_readHexDigit:
    call Readc
    ; check if is a valid hex digit (0-9 -> ascii codes 48 to 57; A-F -> ascii codes 65 to 70)
    ; first check if is between 0 and F(ascii codes 48 to 70)
    ld b, a
    sub a, 48
    jp m, monitor_readHexDigit  ; if negative (s), ascii code is under 48: ignore char
    ld a, b
    sub a, 71   ; 71 because we want to include 70 and the result must be negative
    jp p, monitor_readHexDigit  ; if not negative (ns), ascii code is over 70: ignore it
    ; check if is a valid int (<=57)
    ld a, b
    sub a, 58
    jp p, monitor_readHexDigit_char  ; if not negative (ns), maybe is a char
    ; otherwise is a number! First print for visive feedback
    ld a, b
    call Printc
    ; then convert to its value subtracting 48
    sub a, 48
    ret
    monitor_readHexDigit_char:
    ; check if is A, B, C, D, E, F (ascii codes 65 to 70). We already checked it is less than 70.
    ld a, b
    sub a, 65
    jp m, monitor_readHexDigit  ; if negative (s), ascii code is under 65: ignore char
    ; otherwise is a valid char (A-F). Print for visive feedback
    ld a, b
    call Printc
    ; Its numeric value is 10 (A) to 15 (F). To obtain this, subtract 55.
    sub a, 55
    ret

; Prints a byte in hex format: splits it in two nibbles and prints the two hex digits
; @param a the byte to print
; @uses a, b, c
monitor_printHexByte:
    ld c, a
    ; rotate out the least significant nibble to obtain a byte with the most significant nibble
    ; in the least significant nibble position
    rrca a
    rrca a
    rrca a
    rrca a
    ; the upper nibble must now be discarded
    and %00001111
	call monitor_printHexDigit
    ld a, c
	and %00001111   ; bitwise and: set to 0 the most significant nibble and preserve the least
    call monitor_printHexDigit
	ret

; Prints an hex digit
; @param a provides the byte containing, in the LSBs, the nibble to print
; @uses a, b
monitor_printHexDigit:
    ; check the input is valid (0 to 15)
    ld b, a
    sub 16  ; subtract 16 instead of 15 cause 0 is positive
    ; if positive, the input is invalid. Do not print anything.
    ret p
    ; now check if the digit is a letter (10 to 15 -> A to F)
    ld a, b ; restore a
    sub 10
    ; if a is positive, the digit is a letter
    jp p, monitor_printHexDigit_letter
	ld a, b	; restore a
    ; add 48 (the ASCII number for 0) to obtain the corresponding number
    add 48
	call Printc
    ret
    monitor_printHexDigit_letter:
	ld a, b	; restore a
    ; to obtain the corresponding letter we should subtract 10 (so we count from A)
    ; and add 65 (the ASCII number for A). So -10+65=+55 we add only 55.
    add 55
	call Printc
    ret

; Prints an ASCII character. Similar to system Print function, but
; ignores control characters and replaces any non-printable character with a dot.
; @param a the byte to print
; @uses a, b
monitor_printAsciiByte:
    ld b, a ; save a (it will be modified)
    ; if < 32 is a control char, non printable
    sub 32
    jp m, monitor_printAsciiByte_nonprintable
    ld a, b ; restore a
    ; if >= 127 is an extended char, may not be printable
    sub 127
    jp p, monitor_printAsciiByte_nonprintable
    ; otherwise is a printable ascii char
    ld a, b ; restore a
    call Printc
    ret
    monitor_printAsciiByte_nonprintable:
    ld a, 46 ; print dot
    call Printc
    ret

; Copy data from STDIN to application memory. This is tought to be used with parallel terminal, not keyboard:
; 0s are not ignored and the sequence is complete when no data is available for 8 cpu cycles.
monitor_copyTermToAppMem:
    ld hl, APP_SPACE    ; we will write in APP_SPACE
    ld b, 255; MON_ADB_TIMEOUT     ; the timeout counter (number cycles without available data that represent the end of stream)
    monitor_copyTermToAppMem_loop:
    dec b   ; decrement the timeout counter
    ret 0   ; if counter is 0, timeout reached: return
    ; check if bytes are available
    call Term_availb
    cp 0
    jp z, monitor_copyTermToAppMem     ; no bytes available, next loop
    ; bytes are available
    ld b, 255 ;MON_ADB_TIMEOUT; reset the counter
    ld (hl), a  ; copy byte to memory
    inc hl  ; move to next memory position
    jp monitor_copyTermToAppMem_loop   ; continue loop