
3-26
MPC565/MPC566 Reference Manual
MOTOROLA
OEA Register Set
Signals a decrementer exception request (unless masked) whenever bit 0 of the DEC
changes from zero to one. Multiple DEC exception requests may be received before
the first exception occurs; however, any additional requests are canceled when the
exception occurs for the first request
Signals an exception request if the DEC is altered by software and the content of bit
0 is changed from zero to one
Stops counting and clears the register with PORESET (HRESET/SRESET do not)
The decrementer frequency is based on a subdivision of the processor clock. A bit in the
system clock control register (SCCR) in the SIU determines the clock source of both the
decrementer and the time base. For details on the decrementer and time base clock, refer to
and
The DEC does not run after power-up and must be enabled by setting the TBE bit in the
TBSCR register, see
Table 6-18. Power-on reset stops its counting and clears the register.
A decrementer exception may be signaled to software prior to initialization.
3.9.6
Machine Status Save/Restore Register 0 (SRR0)
The machine status save/restore register 0 (SRR0), SPR 26, identifies where instruction
execution should resume when an rfi instruction is executed following an exception. It also
holds the effective address of the instruction that follows the system call (sc) instruction.
When an exception occurs, SRR0 is set to point to an instruction such that all prior
instructions have completed execution and no subsequent instruction has begun execution.
The instruction addressed by SRR0 may not have completed execution, depending on the
exception type. SRR0 addresses either the instruction causing the exception or the
instruction immediately following. The instruction addressed can be determined from the
exception type and status bits.
MSB
0
123456789
10
11
12
13
14
15
16
17 18 19
20
21
22
23
24
25 26 27 28
29
30
LSB
31
Decrementing Counter
RESET: UNCHANGED
Figure 3-16. DEC — Decrementer Register
MSB
0
123456789
10
11
12
13
14
15
16
17 18 19
20
21
22
23
24
25 26 27 28
29
30
LSB
31
SRR0
RESET: UNDEFINED
Figure 3-17. SRR0 — Machine Status Save/Restore Register 0