GR740-UM-DS, Nov 2017, Version 1.7
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GR740
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LEON4 - Fault-tolerant High-performance SPARC V8 32-bit Processor
6.1
Overview
LEON4 is a 32-bit processor core conforming to the IEEE-1754 (SPARC V8) architecture [SPARC]
with a subset of the V8E extensions [V8E]. It is designed for embedded applications, combining high
performance with low complexity and low power consumption.
The LEON4 core has the following main features: 7-stage pipeline with Harvard architecture, sepa-
rate instruction and data caches, hardware multiplier and divider, on-chip debug support and multi-
processor extensions.
The LEON4 processors in this device have fault-tolerance against SEU errors. The fault-tolerance is
focused on the protection of on-chip RAM blocks, which are used to implement IU/FPU register files
and the L1 cache memory.
6.1.1
Integer unit
The LEON4 integer unit is implemented according to the SPARC V8 manual [SPARC], including
hardware multiply and divide instructions. The number of register windows is eight. The pipeline
consists of 7 stages with a separate instruction and data cache interface.
6.1.2
Cache sub-system
LEON4 has a cache system consisting of a separate instruction and data cache. Both caches have
four ways, four KiB/way, and 32 bytes per line. The instruction cache maintains one valid bit per
cache line and uses streaming during line-refill to minimize refill latency. The data cache has one
valid bit per cache line, uses write-through policy and implements a double-word write-buffer. Bus-
snooping on the AHB bus maintains cache coherency for the data cache.
6.1.3
Floating-point unit and co-processor
The LEON4 integer unit provides interfaces for the high-performance GRFPU floating-point
unit.´The floating-point processor executes in parallel with the integer unit, and does not block the
operation unless a data or resource dependency exists. The floating-point controller and floating-point
unit are further describes in sections 7 and 8.
Integer pipeline
I-Cache
D-Cache
4-Port Register File
AMBA AHB Master (128-bit)
AHB I/F
7-Stage
Interrupt controller
HW MUL/DIV
IEEE-754 FPU
Trace Buffer
Debug port
Interrupt port
Debug support unit
Figure 2.
LEON4 processor core block diagram
SRMMU
DTLB
ITLB