68 lines
2.7 KiB
Markdown
68 lines
2.7 KiB
Markdown
# Bird's Better Bye - Disassembly (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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a collaboration with Peter Ferrie. This new quit routine is far more
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powerful, allowing access to BASIC and binary files (and more), drive
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selection, type-down, more entries, and so on. It runs on older
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hardware than _Bird's Better Bye_ so uses only 40 columns, and does
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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/a2stuff/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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## QUIT.SYSTEM
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This just invokes the ProDOS quit handler immediately. It can
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be used as the last in a chain of "driver" installers.
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