SuperH (SH) 64-bit RISC Series SH-5 System Architecture, Volume ...

PRELIMINARY DATA
88 Debug module
This facility will be used to implement efficient tool/target data communications.
This operation will typically be performed in an environment where tracing may
also be performed at the same time. Thus, it is sensible if the fast printf data is
always written directly to the debug port to avoid interfering with the FIFO
operation.
1.8.3 DM FIFO/trace buffer in target system memory
Note:
The debug module contains a FIFO (see Section 4.1.5: DM FIFO on page 246) which
holds trace messages awaiting transmission to the tool, or waiting to be written into
a trace buffer in the target system’s memory.
The DM.TRCTL.DESTN (Section 1.8.10: DM.TRCTL (trace/trigger register) on page 97)
determines one of the following actions for all trace data loaded into the DM FIFO:
• Trace messages in the DM FIFO are sent to the tool using the currently-selected
debug interface (known as “trace link” mode).
• Trace messages in the DM FIFO are written into an area of target system memory
assigned as a trace buffer (known as “trace buffer” mode). The DM.TRBUF register
(Table 32 on page 107) allows this to be further selected as either “circular trace
buffer” mode or “trace buffer hold” mode. The format is which the trace messages
are written is described in Section 1.8.12: DM.TRPTR (trace pointer register) on
page 110.
In “trace buffer” mode the DM writes the trace messages to target system memory
using SuperHyway Store8/16/32 transactions. These transactions are visible to the
SuperHyway bus analyzers (see Chapter 2: SuperHyway bus analyzer on page 179),
and thus if a bus analyzer is programmed such that it will match on these
transactions, an infinite number of bus analyzer hits (and thus an infinite number of
trace message) will be generated.
• Trace messages remain in the DM FIFO until read by the CPU or by the tool
(known as “DM FIFO trace hold” mode).
D R A FT
• old messages in the DM FIFO are overwritten by new ones so that the DM FIFO
contains the most recent trace messages generated (known as “circular DM FIFO”
mode).
SuperH, Inc.
SH-5 System Architecture, Volume 3: Debug 05-SA-10003 v1.0