jeffv03/4489_byteloader

hardware byteloader for the commodore amiga

4489_byteloader

* small
* portable
* self-contained
* load any number of bytes
* from any disk position
* on any connected drive
* to any memory address
* verifies checksums
* no deadlocks
* graceful timeouts/retries
* respects official hw docs and bulletins
* compatible with iffy /rdy drives
* minimizes head transitions
* does not interfere with existing interrupt, cia timer, blitter or copper use
* tested on A500, A500+, A600, A1200/020, A4000/040
* tested by replacing loaders on ~50 original games (so far) without issue
* updates, issues, improvements:  https://github.com/4489