IEEE-754 Floating Point Unit

The GRFPU performs operations on single and double precision floating-point operands. All operations are IEEE-754 compliant, with exception of denormalized numbers which are flushed to zero. The specified four rounding modes and the detection of exception conditions is fully supported.

An FPU operation is started by providing the operands, opcode and rounding mode on a rising clock edge. The result and the exception flags will be available three clocks later. The FPU is fully pipelined and a new operation can be started every clock cycle. The only exceptions are the FDIV and FSQRT instructions which require between 15 and 24 clock cycles to complete, and which are not pipelined. They are however calculated in a separate non-blocking execution unit, allowing all other operations to be performed in parallel without stalling the FPU pipeline. The table below summarises the throughput and latency of the supported operations:

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Validation

The GRFPU core has been extensively validated with a large set of test vectors. Special test programs such as TestFloat, UCBTEST and IEEE CC754 has been used, as well as floating-point based application software.

LEON FPU Control Unit

The GRFPU can be attached to LEON3 and LEON4 processors through the LEON FPU Control unit (GRFPC). The control unit receives SPARC FPU instructions (FPOP) from the LEON integer unit, and schedules them for execution by the FPU. The FPOPs are executed in parallel with other integer instructions, the LEON pipeline is only stalled in case of operand or resource conflicts. The GRFPC also includes the FPU register file, the processor floating-point status register (FSR) and a deferred trap queue. The GRFPC is available for all versions of the LEON processor.

The IP can be obtained under commercial licensing conditions, enabling proprietary designs and taking advantage of a support agreement.

Contact sales@gaisler.com for licensing information

For evaluation purposes, Xilinx and Altera netlists of GRFPC/GRFPU for LEON2/3 are available from the LEON download page.