Working hex parsing in monitor

assembly/bios/monitor.asm

@@ -5,7 +5,7 @@
 ;   H (HELP) Shows available commands
 ;   D (DUMP) $pos Dumps first 100 bytes of memory starting at $pos
 ;   S (SET) $pos $val Replaces byte at $pos with $val
-;   L (LOAD) $pos $val Loads all the incoming bytes in memory starting from $pos
+;   L (LOAD) $pos $val Loads all the incoming bytes in memory starting from $pos. Ends when "0" is received 8 times.
 ;   R (RUN) $pos Starts executing code from $pos
 ; The commands are entered with a single letter and the program completes the command
 
@@ -19,7 +19,7 @@ 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_ARG_HEX: DB "0x",0
+MON_ARG_HEX: DB "    0x",0
 MON_HELP: DB 10,"Available commands: HELP, DUMP, SET, LOAD, RUN",0
 MON_ERR_SYNTAX: DB "    Syntax error",0
 
@@ -70,6 +70,7 @@ monitor_help:
 monitor_dump:
     ld bc, MON_COMMAND_DUMP + 1 ; autocomplete command
     call Print
+    call monitor_arg_byte
     jp monitor_main_loop
 
 monitor_set:
@@ -88,5 +89,56 @@ monitor_run:
     jp APP_VAR_SPACE    ; Start executing code
     jp monitor_main_loop
 
+monitor_arg_byte:
+    ; Print 0x... prompt
+    ld bc, MON_ARG_HEX
+    call Print
+    ; Receive two hex digits
+    call monitor_readHexDigit
+    call monitor_readHexDigit
+    ret
+
+monitor_arg_2byte:
+    ; Print 0x... prompt
+    ld bc, MON_ARG_HEX
+    call Print
+    ; Receive four hex digits
+    call monitor_readHexDigit
+    call monitor_readHexDigit
+    call monitor_readHexDigit
+    call monitor_readHexDigit
+    ret
+
+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