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434
March 2002 Release
1-800-255-7778
Virtex-II Pro™ Platform FPGA Documentation
Chapter 4:
PPC405 Privileged-Mode Programming Model
R
Device Control Registers
Device control registers (DCRs) are 32-bit registers implemented in FPGA logic gates. They
are not contained within the processor core. The PowerPC embedded-environment
architecture and PowerPC Book-E architecture define the existence of a DCR-address
space and the instructions that access the DCRs, but they do not define what the DCRs do
or how they are to be used. System developers can define DCRs for use in controlling the
operations of on-chip buses, peripherals, and some processor behavior. The processor
reads and writes the DCRs over the DCR-bus interface using the
mfdcr
and
mtdcr
instructions.
See the
for more information on implementing and using
DCRs.
Privileged Instructions
lists the privileged instructions supported by the PPC405. Attempted use of these
instructions when running in user mode causes a program exception.
System Linkage
Application (user-mode) programs transfer control to system-service routines (privileged-
mode programs) using the
system-call
instruction,
sc
. Executing the
sc
instruction causes a
system-call exception to occur. The system-call interrupt handler determines which
system-service routine to call and whether the calling application has permission to call
that service. If permission is granted, the system-call interrupt handler performs the actual
procedure call to the system-service routine on behalf of the application program. This call
is typically performed using a branch instruction that updates the link register with the
return address.
The execution environment expected by the system-service routine requires the execution
of prologue instructions to set up that environment. Those instructions usually create the
block of storage that holds procedural information (the
activation record
), update and
initialize pointers, and save volatile registers (registers the system-service routine uses).
Prologue code can be inserted by the linker when creating an executable module, or it can
be included as stub code in either the system-call interrupt handler or the system-library
routines.
Returns from the system-service routine reverse the process described above. Control is
transferred back to the system-call interrupt handler using a branch to link-register
Table 4-3:
PPC405 Privileged Instructions
System Linkage
Processor Control
Memory-System
Management
Virtual-Memory
Management
rfci
rfi
sc
mfdcr
mfmsr
mfspr
(1)
mtdcr
mtmsr
mtspr
(2)
wrtee
wrteei
dcbi
dccci
dcread
iccci
icread
tlbia
tlbre
tlbsx
tlbsync
tlbwe
Notes:
1.
Except for CTR, LR, SPRG4–SPRG7, and XER.
2.
Except for CTR, LR, and XER.
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