GR740-UM-DS, Nov 2017, Version 1.7
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GR740
latency of four clock cycles at instruction level. The table below shows the GRFPU instruction timing
when used together with GRFPC:
The GRFPC controller implements the SPARC deferred trap model, and the FPU trap queue (FQ) can
contain up to 7 queued instructions when an FPU exception is taken. The version field in %fsr has the
value of 2 to signal that the processor is implemented with the GRFPU.
The GRFPU does not handle denormalized numbers as inputs and will in that case cause an fp_excep-
tion with the FPU trap type set to unfinised_FPOP (tt=2). There is a non-standard mode in the FPU
that will instead replace the denormalized inputs with zero and thus never create this condition.
6.6
Co-processor interface
The coprocessor interface is unused and disabled in this device.
6.7
AMBA interface
6.7.1
Overview
The LEON4 processor has one AHB master interface. The types of AMBA accesses supported and
performed by the processor depend on the accessed memory area’s cachability, if the corresponding
cache is enabled, and if the accessed memory area has been marked as being on the wide bus.
Cacheable instructions are fetched with a burst of two 128-bit accesses.
The HPROT signals of the AHB bus are driven to indicate if the accesses is instruction or data, and if
it is a user or supervisor access.
In case of atomic accesses, a locked access will be made on the AMBA bus to guarantee atomicity as
seen from other masters on the bus.
6.7.2
Cachability
The processor treats the memory areas 0x00000000 - 0x7FFFFFFF and 0xC0000000 - 0xCFFFFFFF
as cacheable. The test of the physical address space is treated as uncached.
Table 41.
GRFPU instruction timing with GRFPC
Instruction
Throughput Latency
FADDS, FADDD, FSUBS, FSUBD,FMULS, FMULD, FSMULD, FITOS, FITOD,
FSTOI, FDTOI, FSTOD, FDTOS, FCMPS, FCMPD, FCMPES. FCMPED
1
4
FDIVS
14
16
FDIVD
15
17
FSQRTS
22
24
FSQRTD
23
25
Table 42.
HPROT values
Type of access User/Super
HPROT
Instruction User
1100
Instruction
Super
1110
Data
User
1101
Data
Super
1111
MMU
Any
1101
