
MOTOROLA
Chapter 5. Exceptions
5-11
Exception Processing
Note that in some implementations, every instruction fetch when MSR[IR] = 1 and every
instruction execution requiring address translation when MSR[DR] = 1 may modify SRR1.
5.2.1.2
CSRR0 and CSRR1 Bit Settings—G2_LE Only
The G2_LE core also implements the CSRR0 and CSRR1 to save state for critical interrupt
exceptions only. Note that the values saved in CSRR0 are the same as those saved in SRR0
for all other exceptions, and the values saved in CSRR1 are the same as those saved in
SRR1 for all other exceptions. However, CSRR0 and CSRR1 have unique SPR numbers,
as described in Chapter 2, “Register Model.”
Figure 5-3 shows the format of CSRR0.
Figure 5-3. Critical Interrupt Save/Restore Register 0 (CSRR0)
When a critical interrupt exception occurs, CSRR0 is set to point to an instruction such that
all prior instructions have completed execution and no subsequent instruction has begun
execution. When an
rfci
instruction is executed, the contents of CSRR0 are copied to the
next instruction address (NIA)—the 32-bit address of the next instruction to be executed.
Figure 5-4 shows the format of CSRR1.
Figure 5-4. Critical Interrupt Save/Restore Register 1 (CSRR1)
When an exception occurs, CSRR1[0–15] are loaded with all zeros and the values of
MSR[16–31] are placed in corresponding CSRR1 bit positions. When
rfci
executes,
MSR[16–31] are loaded from CSRR1[16–31].
CSRR1[0–15] are defined as reserved. An implementation may define one or more of
these bits, and may also cause them to be saved from MSR when an exception is taken,
and restored to MSR from CSRR1 when an
rfci
is executed.
5.2.1.3
SPRG4–SPRG7 (G2_LE Only)
The G2_LE core provides four additional SPRG (SPRG4–SPRG7) registers for general
operating system use, such as performing a fast state save or for supporting multiprocessor
implementations. However, SPRG4–SPRG7 have unique SPR numbers, as described in
Chapter 2, “Register Model.” The formats of SPRG4–SPRG7 are shown in Figure 5-5.
CSRR0
0
29 30
31
Reserved
00
CSRR1
0
31
F
Freescale Semiconductor, Inc.
For More Information On This Product,
Go to: www.freescale.com
n
.