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  • Changes
    • Change FPCSR SPR permissions to allow for reading and writing from user space.
    • Clarify that FPU underflow detection is done by detecting tininess before rounding.
  • Authors Stafford Horne shorne@gmail.com

Details of Additions/Changes

User Mode FPCSR (P17)

2020-05-22 - Stafford Horne

While working on the glibc port for OpenRISC we found that pretty much every architecture allows reading and writing to the floating point control register (in OpenRISC FPCSR) in userland. This is used by userland to control the rounding mode and exception reading and controlling of the FPU.

Tininess Before Rounding (P18)

2021-10-09 - Stafford Horne

The IEEE standard allows specifying how detecting of tininess occurs. Tininess detection is how underflow exceptions are triggered. There are two allowed methods for detecting tininess one is before rounding and the other being after rounding.