Add MEM command, inspired by A2osX's BASIC.FX

COMMANDS

@@ -7,6 +7,7 @@ copy
 date
 echo
 hello
+mem
 online
 type
 touch

README.md

@@ -42,6 +42,7 @@ Sample commands included:
 * `ECHO` - echoes back anything following the command
 * `CD` - like `PREFIX` but accepts `..`, e.g. `cd ../dir`
 * `ONLINE` - lists online volumes (volume name, slot and drive)
+* `MEM` - show memory stats for the BASIC environment
 * `COPY` - copy a single file, e.g. `copy /path/to/file,dstfile`
 * `TYPE` - show file contents (TXT, BAS, or BIN/other), e.g. `type filename`
 * `TOUCH` - apply current ProDOS date/time to a file's modification time, e.g. `touch filename`

mem.cmd.s

@@ -0,0 +1,76 @@
+;;; ============================================================
+;;;
+;;; MEM - Print memory stats
+;;;
+;;; Usage: MEM
+;;;
+;;; Inspiration from A2osX
+;;;
+;;; ============================================================
+
+        .include "apple2.inc"
+        .include "more_apple2.inc"
+
+;;; ============================================================
+
+        .org $4000
+
+        jsr     CROUT
+        jsr     CROUT
+
+.macro  SHOW suffix
+        lda     #<.ident(.concat("str_", .string(suffix)))
+        ldx     #>.ident(.concat("str_", .string(suffix)))
+        ldy     #.ident(.concat("addr_", .string(suffix)))
+        jsr     Print
+.endmacro
+
+        SHOW    pgm_start
+        SHOW    lomem
+        SHOW    array_start
+        SHOW    array_end
+        SHOW    string_start
+        SHOW    himem
+
+        clc
+        rts
+
+addr_pgm_start          := $67
+str_pgm_start:          .byte   "Program start: $", 0
+addr_lomem              := $69
+str_lomem:              .byte   "LOMEM:         $", 0
+addr_array_start        := $6B
+str_array_start:        .byte   "Array start:   $", 0
+addr_array_end          := $6D
+str_array_end:          .byte   "Array end:     $", 0
+addr_string_start       := $6F
+str_string_start:       .byte   "String start:  $", 0
+addr_himem              := $73
+str_himem:              .byte   "HIMEM:         $", 0
+
+.proc Print
+        sta     msg_addr
+        stx     msg_addr+1
+        iny                     ; MSB first
+        sty     zp_addr
+
+        ldx     #0
+        msg_addr := *+1
+loop:   lda     $1234,x         ; self-modified
+        beq     :+
+        ora     #$80
+        jsr     COUT
+        inx
+        bne     loop            ; always
+:
+        jsr     getb
+        jsr     PRBYTE
+        jsr     getb
+        jsr     PRBYTE
+        jmp     CROUT
+
+        zp_addr := *+1
+getb:   lda     $12             ; self-modified
+        dec     zp_addr
+        rts
+.endproc