Add readme
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Joshua Bell
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# Bird's Better Bye - Diassembly (and improvements)
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The ProDOS operating system for the Apple II personal computer line
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supported a quit routine (invoked from BASIC with the `BYE` command)
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allowing the user to type the name of a system file to invoke once
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the previous system file had exited.
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[Alan Bird](https://alanlbird.wordpress.com/products/) wrote a
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replacement called **Bird's Better Bye** that would patch itself into
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ProDOS, fitting into a tight 768 bytes. It provides a menu system,
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allowing selection of system files (with the arrow keys), directories
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(with the return key to enter and escape key to exit), and devices
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(with the tab key), with a minimal and stylish 80-column display using
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MouseText folder glyphs.
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Later official versions of ProDOS replaced the previous quit routine
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with _Bird's Better Bye_.
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## ProDOS 2.4 / Bitsy Bye
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The new (unofficial) releases of
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[ProDOS 2.4](http://www.callapple.org/uncategorized/announcing-prodos-2-4-for-all-apple-ii-computers/)
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by John Brooks include a replacement quit routine called Bitsy Bye.
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This new quit routine is far more powerful, allowing access to BASIC
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and binary files (and more), drive selection, type-down, more entries,
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and so on. It runs on older hardware than _Bird's Better Bye_ so
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uses only 40 columns, and does not require a 65C02 processor.
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Impressed though I am with the power of Bitsy Bye, I am not a fan of
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its aesthetics - the display is "cluttered" to my eye.
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## BYE.SYSTEM
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Aeons ago, Dave Cotter created BYE.SYSTEM which would patch _Bird's
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Better Bye_ back into ProDOS if it had been replaced. It can be found
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at:
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http://www.lazilong.com/apple_ii/bye.sys/bye.html
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Since I really liked the look of _Bird's Better Bye_ I used this as
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the boot system for my virtual hard drive (occuring after some [clock
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drivers](https://github.com/inexorabletash/cricket)).
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## Buh-Bye
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But... I really wanted a way to quickly scroll through my games list.
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So I set out to improve _Bird's Better Bye_ by disassembling it (and
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the `BYE.SYSTEM` installer), thus ending up with "Bell's Better Bird's
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Better Bye" or "Buh-Bye" for short.
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The changes are so far pretty minimal since my 6502 skills are not,
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in fact, mad, and there are only 768 bytes to play with.
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I replaced the directory enumeration logic with tighter code as
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outlined in the ProDOS Technical Reference Manual, and along with
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other optimizations I made enough room to add seeking if an
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alphabetical key is typed (hit 'C' and the list will scroll to the
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next file starting with 'C').
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There are a few spare bytes to play with and more can be squeezed
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out, so perhaps further improvements can be made.
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@ -237,11 +237,11 @@ while_loop:
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ldy #FileEntry::file_type
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lda (entry_pointer),y
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cmp #FileType::Directory
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beq good_entry
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beq store_entry
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cmp #FileType::System
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bne done_active_entry
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good_entry:
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store_entry:
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;; Store type
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ldx num_entries
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sta types_table,x
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@ -339,8 +339,9 @@ close_dir:
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: stz current_entry
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stz page_start
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lda num_entries
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beq keyboard_loop ; no entries (empty directory)
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beq selection_loop_keyboard_loop ; no entries (empty directory)
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;; Draw entries
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cmp #bottom_row ; more entries than fit?
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bcc :+
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lda #(bottom_row - top_row + 1)
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@ -356,7 +357,7 @@ loop: jsr draw_current_line
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dec row_count
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bne loop
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stz current_entry
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beq draw_current_line_inv
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beq selection_loop
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.endproc
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;;; ------------------------------------------------------------
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@ -382,19 +383,19 @@ handy_rts:
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.proc on_down
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jsr down_common
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bra draw_current_line_inv
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bra selection_loop
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.endproc
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;;; ------------------------------------------------------------
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.proc on_up
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ldx current_entry
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beq draw_current_line_inv ; first one? just redraw
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dec current_entry ; go to previous
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ldx current_entry ; first one?
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beq selection_loop
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dec current_entry ; go to previous
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lda CV
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cmp #top_row ; at the top?
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bne draw_current_line_inv ; if not, just draw
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bne selection_loop
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dec page_start ; yes, adjust page and
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lda #ASCII_SYN ; scroll screen up
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jsr COUT
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@ -403,14 +404,11 @@ handy_rts:
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;;; ------------------------------------------------------------
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draw_current_line_inv:
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.proc selection_loop
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jsr SETINV
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jsr draw_current_line
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;; fall through
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;;; ------------------------------------------------------------
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.proc keyboard_loop
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keyboard_loop:
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lda KBD
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bpl keyboard_loop
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sta KBDSTRB
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@ -436,6 +434,7 @@ draw_current_line_inv:
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beq on_up
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;; fall through
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.endproc
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selection_loop_keyboard_loop := selection_loop::keyboard_loop
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;;; ------------------------------------------------------------
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@ -446,7 +445,7 @@ loop: jsr down_common
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and #$5F ; make ASCII and uppercase
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ldy #1
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cmp (curr_ptr),y ; key = first char ?
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beq draw_current_line_inv
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beq selection_loop
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bra loop
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.endproc
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@ -466,7 +465,7 @@ loop: jsr down_common
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bcc :+
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pla ; yes - abort subroutine
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pla
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bra draw_current_line_inv
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bra selection_loop
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: sta current_entry ; go to next
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