There are certain 68k CPUs that lack FPU! These are 68000, 68020, 68030, 68LC040, 68EC040, 68LC060, and 68EC060. These CPUs are all quite cheap to get. Especially the LC variants of 68040 and 68060 can be purchased for as low as 50 Euro on sites such as eBay. Do not get the EC version though as that one also lacks MMU which cannot be emulated.
Because the non-FPU 68k variants lack FPU, it means that software that expects the 68060 FPU to be there for AmigaOS cannot be used unless you install SoftIEEE which provides both a high-precision mathematical floating point library for floating point operations and a software-based FPU emulator.
SoftIEEE simply adds a “virtual FPU” to your system. Without SoftIEEE installed, you should run software such as the IBrowse 68030 non-FPU version of the web browser for AmigaOS.
SoftIEEE saves the day for LC 68k Users
With this virtual software package, you can run software such as 68060 software that is looking for the FPU. You can then install and use SoftIEEE for it to work. In fact, SoftIEEE works for all of the FPU-less Motorola processors, from 68000 to 68LC060.
Yes. This virtual FPU software also works for 68000! but it is very slow. So, since 68LC040 and 68LC060 are so much more powerful. It is recommended to use SoftIEEE with them.
But there are also limitations as only some demos seem to work correctly. However, the FPU handling in the most 3D intense made demos will have issues. SoftIEEE is a must-have for LC and EC (do not get it unless you really want it) users so you will not have a guru if you run FPU software. Handling illegal instructions is slow though.
Installation instructions to Follow
- 1) Copy the softieee.library to LIBS:
This library implements the numerical algorithms of the FPU, such as addition, multiplication… and also transcental
functions such as sin() and cos(). The library can also be used without the FPU emulation for high-precision mathematics. It is approximately equivalent to the mathieeedoubbas/doubtrans system libraries, but is able to compute in single, double and extended precision, through a single unified code.
- 2) Copy SoftIEEE to C:
This binary is the actual FPU implementation that uses the softieee.library for the numerical algorithms.
- 3) Run SoftIEEE in the startup-sequence
This must be set somewhere below SetPatch. There are typically no arguments required.
Due to emulation, executables of FPU software may require approximately 400 bytes more stack. Thus, it may be wise to increase
the default stack size by this amount.
Thanks to Thomas Richter for this very useful SoftIEEE software that helps 68k users without FPU a lot. He just released an update, so go onto Aminet and grab it if you need it for your Classic Amiga.