COBHAM GR740 User Manual

GR740-UM-DS, Nov 2017, Version 1.7 482 www.cobham.com/gaisler
GR740
43.2 Change and errata descriptions
43.2.1 LEON4 and Level-2 cache fault-tolerance
Corner cases were found in the Level-2 cache handling of correctable and uncorrectable errors that
require additional precautions to be taken in software if the device is exposed to single event effects.
The corner cases can also be triggered with error injection in Level-2 cache and external SDRAM.
The corrections implemented in the Level-2 cache also adds new register fields to control L2 cache
functionality. These new fields are documented in section 9.4.
Workaround: Recommendations on software workarounds are available to protoflight users.
Applicable to: These limitations are only present in silicon revision 0. Silicon revision 0 should not
be used in radiation tests or for fault injection.
43.2.2 LEON4 DBPM function error
When the DBPM (disable branch prediction on instruction cache miss) function is enabled in the
LEON4 processor, there is a corner case where execution flow might go wrong when an interrupt hap-
pens. This bug does not have any effect until the instruction cache is enabled. The DPBM function
was added as a new feature to GR740 and not present in earlier LEON4 devices, the workaround to
turn this off reverts back to the previous behavior without any other side effects.
The bug is triggered by the instruction sequence:
#1. compare
#2. conditional branch to #4, correctly predicted (taken)
#3. compare in delay slot of #2
#4. conditional branch with annul, mispredicted (not taken)
#5. some instruction in delay slot of #4, gets annulled
For the bug to manifest, the following condition must also be true:
• branch prediction enabled, DBPM function enabled (%asr17 bit 25)
• instruction #5 not in cache (fetch deferred by DBPM logic)
• IRQ taken on instruction #4
22 SDRAM controller bus parking functionality Added functionality in revi-
sion 1. Backward compatible
change.
23 Missing SpaceWire router AMBA configuration port registers Affected Not affected
24 SpaceWire router AMBA configuration port interrupt Added functionality in revi-
sion 1. Backward compatible
change.
25 SpaceWire: FCT must be sent before entering run-state Modified behaviour
26 SpaceWire TDP: Extend functionality Added functionality in revi-
sion 1. Backward compatible
change.
27 GRFPU Floating Point Controller: Missing FDIV/FSQRT result Affected Not affected
Table 602.Changes and errata vs device revisions
No. Name / Description Device silicon revision
01

COBHAM GR740 Specifications

General

Brand	COBHAM
Model	GR740
Category	Computer Hardware
Language	English