contents of the EVPR and the low-order 16 bits of the program counter are written with Ox1000.
Interrupt
processing begins at the address
in
the program counter.
To
clear a PIT interrupt, the interrupt handling routine must clear the PIT interrupt bit, TSR[PIS].
Clearing
is performed by writing a word to TSR, using an
mtspr
instruction, that has 1
in
bit positions
to be
cleared and 0
in
all other bit positions. The data written to the TSR is not direct data, but a mask;
a 1
clears the bit and 0 has no effect.
Executing an rfi instruction restores the program counter from
SRRO
and the MSR from
SRR1
, and
execution resumes at the address
in
the program counter.
Table
10-18.
Register
Settings
during
Programmable
Interval
Timer
Interrupts
SRRO
Written with the address of the next instruction to be executed
SRR1
Written with the contents of the MSR
MSR
WE, EE, PR, OWE, IR, DR
~
0
CE, ME, DE
~
unchanged
PC
EVPR[O:15]II Ox1000
TSR
PIS~
1
10.21 Fixed Interval Timer (FIT) Interrupt
For a discussion of the PPC405GP timer facilities, see Chapter 11, "Timer Facilities:' The FIT is
described
in
"Fixed Interval Timer (FIT) Interrupt" on page 10-42.
If
the FIT interrupt is enabled by TCR[FIE] and MSR[EE], the PPC405GP initiates a FIT interrupt after
detecting a time-out from the
FIT.
Time-out is detected when, at the beginning of a clock cycle,
TSR[FIS]
=
1.
(This occurs on the second cycle after the 0
~
1 transition of the appropriate time-base
bit.) The
PPC405GP immediately takes the interrupt. The address of the next sequential instruction is
written into
SRRO;
simultaneously, the contents of the MSR are written into SRR1 and the MSR
is
written with the values shown
in
Table 10-19. The high-order 16 bits of the program counter are then
written with the contents of the EVPR and the
low-order 16 bits of the program counter are written
with
Ox1
01
O.
Interrupt processing begins at the address
in
the program counter.
To
clear a FIT interrupt, the interrupt handling routine must clear the FIT interrupt bit, TSR[FIS].
Clearing
is performed by writing a word to TSR, using an
mtspr
instruction, that has 1 in any bit
positions to be
cleared and 0
in
all other bit positions. The data written to the TSR is not direct data,
but a mask; a 1
clears a bit and 0 has no effect.
Executing an rfi instruction restores the program counter from
SRRO
and the MSR from SRR1, and
execution resumes at the address in the program counter.
Table
10-19.
Register
Settings
during
Fixed
Interval
Timer
Interrupts
SRRO
Written with the address of the next sequential instruction
SRR1
Written with the contents of the MSR
MSR
WE, EE, PR, OWE, IR, DR
~
0
CE, ME, DE
~
unchanged
PC
EVPR[O:15]II Ox1010
TSR
FIS~
1
10-42
PPC405GP User's Manual
Preliminary
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