FPEmulator_SaveContext (changes)
Showing changes from revision #0 to #1:
Added | Removed | Changed
FPEmulator
» SWI Calls
» FPEmulator_SaveContext
FPEmulator_SaveContext
(SWI &40489)
| Entry | |
|---|---|
| R0 | Pointer to context (-2 for current context) |
| R1 | Pointer to 25-word area as described under FPEmulator_SaveContext |
| R2 | PC value associated with the context |
| Exit | |
|---|---|
| R0 | non-zero if there is a pending or incompletely processed exception associated with the context, zero if there isn’t |
Output Format
| Offset | Value |
|---|---|
| 0 | FPSR value |
| 4 | F0 value, as an extended precision number |
| 16 | F1 value, as an extended precision number |
| 28 | F2 value, as an extended precision number |
| 40 | F3 value, as an extended precision number |
| 52 | F4 value, as an extended precision number |
| 64 | F5 value, as an extended precision number |
| 76 | F6 value, as an extended precision number |
| 88 | F7 value, as an extended precision number |
Use
The purpose of this call is to save the register and FPSR values held in a floating point context to a specified 25-word area of memory.
Notes
Note that it does this without processing any pending exceptions associated with the context, or completing the processing of any exception which is currently being processed. The routine returns a hint about whether there is a pending or incompletely processed exception associated with the context: if there is, the values returned may be rather odd and should not be relied upon as an accurate reflection of reality. For instance, if the FPA has a pending overflow exception, the destination register of the instruction concerned will often read as containing a very small number!
This call might be used by a debugger to view the current FP register contents. The PC value passed in would then be the address at which execution was interrupted – it is used to detect whether the floating point system was interrupted in the middle of processing an exception.
Contexts are only available from FPEmulator 4.12 and later.
This call did not work correctly until version 4.17 of the FPEmulator module.
See also
Social
and
ROOL Store
Buy RISC OS Open merchandise here, including SD cards for Raspberry Pi and more.