bk_rangercheck

Short:        Replace exec.library's RangerMem check
Author:       henryk.richter@gmx.net (Henryk Richter)
Uploader:     henryk richter gmx net (Henryk Richter)
Type:         util/boot
Requires:     util/boot/BlizKick or Remus
Architecture: m68k-amigaos

This blizkick module (usable in Remus, as well) replaces the Ranger Mem detection 
routine in exec.library by a complete rewrite. The Ranger Mem is also known as
A500 Slow RAM or $C0 RAM. Although expansions for this type of RAM are only 
available to the 16 Bit Amigas (A500/A2000, possibly A1000), this check is present
in all exec versions. 

There were two reasons for me to dig into this. For one, the original routine 
occasionally mis-detects memory when the kickstart is executed from local FastRAM.
In addition, checked memory locations are not restored after testing, potentially
destroying reset-proof data (like RAD: or resident kickstart modules).

My replacement routine avoids these two issues while still carefully navigating
through the memory layout, where the $C0 range mirrors to the custom register range
on some computers. Extensive tests have been performed on several Amiga models 
to date (A500/A600/A2000/A1200/A4000). The replacement routine is even shorter
than the original. 

I've placed the code into public domain but would still appreciate attribution, 
if my routine is re-used in any project.

The replacement was tested with the following exec versions, so far:
- 34.5  (1.3)
- 40.10 (3.1)
- 45.20 (3.9BB2)
- 45.23 (3.X)

Rostock, 03-Aug-2017, Henryk Richter

Usage instructions in Remus (brief)
- set up the list of modules to be included in kickstart (as usual)
- place  the rangermem module into the list of modules, somewhere after "exec"
- if the rangermem module doesn't report a failure on "compile", then the patch
  was successfully applied

History
0.3 - changed register usage to make it work with Kick1.3 better
0.2 - fixed a typo in the definitions, previously broke A2000 support
0.1 - first test