VFP Execution Environment (Rev #5, changes)
Showing changes from revision #4 to #5:
Added | Removed | Changed
Goals
( There is currently a bias towards using the olderAPCS amendments and compiler/OS support to allow its use by programs/Selecting !RunImage when both FPA and instruction set for floating point operations ostensiby because the majority of VFP RISC binaries OS provided) systems were based around the ARM7500FE or lacked floating point hardware entirely – and in that situation a floating point emulator was a good way to have code be able to run in either scenario.
Since ARM11 the scales have tipped the other way as these cores implement one variant or another of the VFP hardware macrocell, Arm’s replacement for the FPA. Ignoring VFPv1, since RISC OS never ran on any of the chips and version 1 has since been obsoleted, this means VFPv2 or VFPv3 or VFPv4.
To proposal looks at how to better integrate hardware floating point support within RISC OS, primarily for those clients of the Shared C Library, but also setting out examples by which hardware floating point support can be detected so that when multiple variants are supplied the correct one is run.
Existing documentation
Relevant specifications
Relevant forum threads
Terminology
FPA is the original Floating Point Accelerator, coprocessor numbers 1 & 2 for the ARM.
VFP is the Vector Floating Point unit, coprocessor numbers 10 & 11 for the ARM.
The APCS is the ARM Procedure Calling Standard, treated as a synonym here for ATPCS (for ARM/Thumb PCS), and AAPCS (for ARM Architecture PCS).
An ABI defines an Application Binary Interface, comprising a base ABI for the core-registers only and basis for several variants.
Detail
APCS amendments
The Shared C Library
Client registration
Code which is not a client of the Shared C Library)
Toolchain switches
Disc based components
ROM based components
VFP Emulator
NEON and the NeVer condition code
Why not retrofit FPEmulator?
Selecting a !RunImage
Implementation progress
| Phase | Status | Completion | Latest updates |
|---|---|---|---|
| Conceptual design | In progress | 0% | 26-Dec-2021 Document created |
| Mock ups/visualisation | - | - | - |
| Prototype coding | - | - | - |
| Final implementation | - | - | - |
| Testing/integration | - | - | - |
Document history
v1.00 – 26-Dec-2021
- Outline added
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