MPC555
/
MPC556
DEVELOPMENT SUPPORT
MOTOROLA
USER’S MANUAL
Rev. 15 October 2000
21-4
21.2.1.2 History Buffer Flushes Status Pins— VFLS [0..1]
The history buffer flushes status pins denote how many instructions are flushed from
the history buffer this clock due to an exception.
shows VFLS encodings.
21.2.1.3 Queue Flush Information Special Case
There is one special case when although queue flush information is expected on the
VF pins, (according to the last value on the VF pins), regular instruction type informa-
tion is reported. The only instruction type information that can appear in this case is VF
= 111, branch (direct or indirect) NOT taken. Since the maximum queue flushes pos-
sible is five, it is easy to identify this special case.
21.2.2 Program Trace when in Debug Mode
When entering debug mode an
interrupt/exception taken
is reported on the VF pins,
(VF = 100) and a cycle marked with the program trace cycle is made visible externally.
When the CPU is in debug mode, the VF pins equal ‘000’ and the VFLS pins equal
‘11’. For more information on debug mode refer to
21.4 Development System Inter-
If VSYNC is asserted/negated while the CPU is in debug mode, this information is re-
ported as the first VF pins report when the CPU returns to regular mode. If VSYNC
was not changed while in debug mode. the first VF pins report will be of an indirect
branch taken (VF = 101), suitable for the
rfi
instruction that is being issued. In both
Table 21-2 VF Pins Queue Flush Encodings
VF[0:2]
Queue Flush Information
000
0 instructions flushed from instruction queue
001
1 instruction flushed from instruction queue
010
2 instructions flushed from instruction queue
011
3 instructions flushed from instruction queue
100
4 instructions flushed from instruction queue
101
5 instructions flushed from instruction queue
110
Reserved
111
Instruction type information
1
NOTES:
1. Refer to
Table 21-3 VFLS Pin Encodings
VFLS[0:1]
History Buffer Flush Information
00
0 instructions flushed from history queue
01
1 instruction flushed from history queue
10
2 instructions flushed from history queue
11
Used for debug mode indication (FREEZE). Program trace ex-
ternal hardware should ignore this setting.
F
re
e
sc
a
le
S
e
m
ic
o
n
d
u
c
to
r,
I
Freescale Semiconductor, Inc.
For More Information On This Product,
Go to: www.freescale.com
n
c
.
..