Chapter 8 S12X Debug (S12XDBGV3) Module
MC9S12XE-Family Reference Manual , Rev. 1.19
338
Freescale Semiconductor
8.4.5.4
Reading Data from Trace Buffer
The data stored in the Trace Buffer can be read using either the background debug module (BDM) module,
the XGATE or the CPU12X provided the S12XDBG module is not armed, is configured for tracing and
the system not secured. When the ARM bit is written to 1 the trace buffer is locked to prevent reading. The
trace buffer can only be unlocked for reading by an aligned word write to DBGTB when the module is
disarmed.
The Trace Buffer can only be read through the DBGTB register using aligned word reads, any byte or
misaligned reads return 0 and do not cause the trace buffer pointer to increment to the next trace buffer
address. The Trace Buffer data is read out first-in first-out. By reading CNT in DBGCNT the number of
valid 64-bit lines can be determined. DBGCNT will not decrement as data is read.
Whilst reading an internal pointer is used to determine the next line to be read. After a tracing session, the
pointer points to the oldest data entry, thus if no overflow has occurred, the pointer points to line0,
otherwise it points to the line with the oldest entry. The pointer is initialized by each aligned write to
DBGTBH to point to the oldest data again. This enables an interrupted trace buffer read sequence to be
easily restarted from the oldest data entry.
6
CSZ
Access Type Indicator
— This bit indicates if the access was a byte or word size access.This bit only contains
valid information when tracing CPU12X activity in Detail Mode.
0 Word Access
1 Byte Access
5
CRW
Read Write Indicator
— This bit indicates if the corresponding stored address corresponds to a read or write
access. This bit only contains valid information when tracing CPU12X activity in Detail Mode.
0 Write Access
1 Read Access
4
COCF
CPU12X Opcode Fetch Indicator
— This bit indicates if the stored address corresponds to an opcode fetch
cycle. This bit only contains valid information when tracing the XGATE accesses in Detail Mode.
0 Stored information does not correspond to opcode fetch cycle
1 Stored information corresponds to opcode fetch cycle
3
XACK
XGATE Access Indicator
— This bit indicates if the stored XGATE address corresponds to a free cycle. This bit
only contains valid information when tracing the CPU12X accesses in Detail Mode.
0 Stored information corresponds to free cycle
1 Stored information does not correspond to free cycle
2
XSZ
Access Type Indicator
— This bit indicates if the access was a byte or word size access. This bit only contains
valid information when tracing XGATE activity in Detail Mode.
0 Word Access
1 Byte Access
1
XRW
Read Write Indicator
— This bit indicates if the corresponding stored address corresponds to a read or write
access. This bit only contains valid information when tracing XGATE activity in Detail Mode.
0 Write Access
1 Read Access
0
XOCF
XGATE Opcode Fetch Indicator
— This bit indicates if the stored address corresponds to an opcode fetch
cycle.This bit only contains valid information when tracing the CPU12X accesses in Detail Mode.
0 Stored information does not correspond to opcode fetch cycle
1 Stored information corresponds to opcode fetch cycle
Table 8-46. CXINF Field Descriptions (continued)
Field
Description
Because
of
an
order
from
the
United
States
International
Trade
Commission,
BGA-packaged
product
lines
and
part
numbers
indicated
here
currently
are
not
available
from
Freescale
for
import
or
sale
in
the
United
States
prior
to
September
2010:
S12XE
products
in
208
MAPBGA
packages
