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March 2002 Release
Virtex-II Pro™ Platform FPGA Documentation
1-800-255-7778
R
First Instruction
After the processor completes the hardware-initialization sequence caused by
a reset, it performs an instruction fetch from the address 0xFFFF_FFFC. This
first instruction is typically an unconditional branch to the initialization code.
If the instruction at this address is not a branch, instruction fetching wraps to
address 0x0000_0000. The system must be designed to provide non-volatile
memory that contains the first instruction and the initialization code.
Because the processor is initially in big endian mode, initialization code must
be in big endian format. It must remain in big endian format until memory
and the processor are configured for little-endian operation.
Initialization
During reset, the minimum number of resources required for software
execution are initialized by the processor. Initialization software is generally
required to fully configure both the processor and system for normal
operation. The following provides a checklist of tasks the initialization code
should follow when performing this configuration.
1.
Configure the real-mode memory system by updating the storage-
attribute control registers.
-
After reset, all memory is marked as guarded storage, preventing
speculative instruction fetches. To improve fetch performance, the
Table 10-2:
SPR Contents Following Reset
Register
Value
Comment
DBCR0
0x0000_0000
Debug modes, events, and instruction comparisons are disabled.
DBCR1
0x0000_0000
Data comparisons are disabled.
DBSR
Undefined
1
Most-recent reset (MRR) is set as specified in the note.
DCCR
0x0000_0000
Data-cache is disabled.
ESR
0x0000_0000
No exception syndromes are recorded.
ICCR
0x0000_0000
Instruction-cache is disabled.
PVR
0x2001_0820
Identifies the processor.
SGR
0xFFFF_FFFF
All memory is guarded.
SLER
0x0000_0000
All memory is big endian.
SU0R
0x0000_0000
All user-defined memory attributes are disabled.
TCR
Undefined
2
Watchdog-reset control (WRC) is cleared.
TSR
Undefined
1
Most-recent watchdog reset (WRS) is set as specified in the note.
Notes:
1.
The most-recent reset bits are set as follows:
00—No reset occurred. This is the value of WRS if the watchdog timer
did not
cause the reset.
01—A processor-only reset occurred.
10—A chip reset occurred.
11—A system reset occurred.
2.
WRC is cleared, disabling watchdog time-out resets.
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