PC912XDP512F0MPVR datasheet(725/1348 Pages) FREESCALE

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Chapter 19 S12X Debug (S12XDBGV2) Module

MC9S12XDP512 Data Sheet, Rev. 2.21

Freescale Semiconductor

727

19.4.5.3.2

Reading Data from Trace Buffer

The data stored in the trace buffer can be read using either the background debug module (BDM) module

or the CPU provided the DBG module is not armed, is conﬁgured for tracing (at least one TSOURCE bit

is set) 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 a single aligned word write to DBGTB when

the module is disarmed. Multiple writes to the DBGTB are not allowed since they increment the pointer.

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.

The least signiﬁcant word of each 64-bit wide array line is read out ﬁrst. This corresponds to the bytes 1

and 0 of Table 19-39. The bytes containing invalid information (shaded in Table 19-39) are also read out.

Reading the trace buffer while the DBG module is armed will return invalid data and no shifting of the

RAM pointer will occur. Reading the trace buffer is not possible if both TSOURCE bits are cleared.

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 Read/Write Access

1 Access

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 CPU accesses in detail mode.

0 Stored information does not correspond to opcode fetch cycle

1 Stored information corresponds to opcode fetch cycle

Table 19-42. CXINF Field Descriptions (continued)

Field

Description

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