Add readme

README.md

@@ -0,0 +1,61 @@
+# Bird's Better Bye - Diassembly (and improvements)
+
+The ProDOS operating system for the Apple II personal computer line
+supported a quit routine (invoked from BASIC with the `BYE` command)
+allowing the user to type the name of a system file to invoke once
+the previous system file had exited.
+
+[Alan Bird](https://alanlbird.wordpress.com/products/) wrote a
+replacement called **Bird's Better Bye** that would patch itself into
+ProDOS, fitting into a tight 768 bytes. It provides a menu system,
+allowing selection of system files (with the arrow keys), directories
+(with the return key to enter and escape key to exit), and devices
+(with the tab key), with a minimal and stylish 80-column display using
+MouseText folder glyphs.
+
+Later official versions of ProDOS replaced the previous quit routine
+with _Bird's Better Bye_.
+
+## ProDOS 2.4 / Bitsy Bye
+
+The new (unofficial) releases of
+[ProDOS 2.4](http://www.callapple.org/uncategorized/announcing-prodos-2-4-for-all-apple-ii-computers/)
+by John Brooks include a replacement quit routine called Bitsy Bye.
+This new quit routine is far more powerful, allowing access to BASIC
+and binary files (and more), drive selection, type-down, more entries,
+and so on. It runs on older hardware than _Bird's Better Bye_ so
+uses only 40 columns, and does not require a 65C02 processor.
+
+Impressed though I am with the power of Bitsy Bye, I am not a fan of
+its aesthetics - the display is "cluttered" to my eye.
+
+## BYE.SYSTEM
+
+Aeons ago, Dave Cotter created BYE.SYSTEM which would patch _Bird's
+Better Bye_ back into ProDOS if it had been replaced. It can be found
+at:
+
+http://www.lazilong.com/apple_ii/bye.sys/bye.html
+
+Since I really liked the look of _Bird's Better Bye_ I used this as
+the boot system for my virtual hard drive (occuring after some [clock
+drivers](https://github.com/inexorabletash/cricket)).
+
+## Buh-Bye
+
+But... I really wanted a way to quickly scroll through my games list.
+So I set out to improve _Bird's Better Bye_ by disassembling it (and
+the `BYE.SYSTEM` installer), thus ending up with "Bell's Better Bird's
+Better Bye" or "Buh-Bye" for short.
+
+The changes are so far pretty minimal since my 6502 skills are not,
+in fact, mad, and there are only 768 bytes to play with.
+
+I replaced the directory enumeration logic with tighter code as
+outlined in the ProDOS Technical Reference Manual, and along with
+other optimizations I made enough room to add seeking if an
+alphabetical key is typed (hit 'C' and the list will scroll to the
+next file starting with 'C').
+
+There are a few spare bytes to play with and more can be squeezed
+out, so perhaps further improvements can be made.

buhbye.system.s

@@ -237,11 +237,11 @@ while_loop:
         ldy     #FileEntry::file_type
         lda     (entry_pointer),y
         cmp     #FileType::Directory
-        beq     good_entry
+        beq     store_entry
         cmp     #FileType::System
         bne     done_active_entry
 
-good_entry:
+store_entry:
         ;; Store type
         ldx     num_entries
         sta     types_table,x
@@ -339,8 +339,9 @@ close_dir:
 :       stz     current_entry
         stz     page_start
         lda     num_entries
-        beq     keyboard_loop   ; no entries (empty directory)
+        beq     selection_loop_keyboard_loop   ; no entries (empty directory)
 
+        ;; Draw entries
         cmp     #bottom_row     ; more entries than fit?
         bcc     :+
         lda     #(bottom_row - top_row + 1)
@@ -356,7 +357,7 @@ loop:   jsr     draw_current_line
         dec     row_count
         bne     loop
         stz     current_entry
-        beq     draw_current_line_inv
+        beq     selection_loop
 .endproc
 
 ;;; ------------------------------------------------------------
@@ -382,19 +383,19 @@ handy_rts:
 
 .proc on_down
         jsr     down_common
-        bra     draw_current_line_inv
+        bra     selection_loop
 .endproc
 
 ;;; ------------------------------------------------------------
 
 .proc on_up
-        ldx     current_entry
-        beq     draw_current_line_inv ; first one? just redraw
-        dec     current_entry         ; go to previous
+        ldx     current_entry   ; first one?
+        beq     selection_loop
+        dec     current_entry   ; go to previous
 
         lda     CV
         cmp     #top_row        ; at the top?
-        bne     draw_current_line_inv ; if not, just draw
+        bne     selection_loop
         dec     page_start      ; yes, adjust page and
         lda     #ASCII_SYN      ; scroll screen up
         jsr     COUT
@@ -403,14 +404,11 @@ handy_rts:
 
 ;;; ------------------------------------------------------------
 
-draw_current_line_inv:
+.proc selection_loop
         jsr     SETINV
         jsr     draw_current_line
-        ;; fall through
 
-;;; ------------------------------------------------------------
-
-.proc keyboard_loop
+keyboard_loop:
         lda     KBD
         bpl     keyboard_loop
         sta     KBDSTRB
@@ -436,6 +434,7 @@ draw_current_line_inv:
         beq     on_up
         ;; fall through
 .endproc
+        selection_loop_keyboard_loop := selection_loop::keyboard_loop
 
 ;;; ------------------------------------------------------------
 
@@ -446,7 +445,7 @@ loop:   jsr     down_common
         and     #$5F            ; make ASCII and uppercase
         ldy     #1
         cmp     (curr_ptr),y    ; key = first char ?
-        beq     draw_current_line_inv
+        beq     selection_loop
         bra     loop
 .endproc
 
@@ -466,7 +465,7 @@ loop:   jsr     down_common
         bcc     :+
         pla                     ; yes - abort subroutine
         pla
-        bra     draw_current_line_inv
+        bra     selection_loop
 
 :       sta     current_entry   ; go to next