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

PRELIMINARY DATA
120 Debug protocols and interfaces
Each WP channel’s action register allows the type of trace message generated to be
defined. See Section 1.5: Debug event actions on page 48.
Encoding of address offsets
To minimize the sizes of trace messages being sent over the SHdebug link, program
counter addresses, and bus analyzer addresses are compressed wherever possible.
However, when the trace destination is configured as “DM FIFO trace hold”,
“circular DM FIFO”, “circular trace buffer” or “trace buffer hold” mode, addresses
are always encoded as absolute values. This allows trace to be reconstructed even if
some trace packets are lost, as each message can be interpreted without reference to
other messages.
An encoding method is used whereby either one or two bytes are used to represent
signed address offsets as either a 7-bit or a 15-bit 2’s complement value. These
offsets are relative to the previous address of the same type. If the address cannot be
expressed as an offset, an absolute 32-bit value is encoded instead. Therefore:
• Program counter addresses are stored as effective addresses, and are encoded
either as an 32-bit absolute address, or as a 7-bit or 15-bit 2’s complement value
relative to the previous PC address.
• Bus analyzer addresses are encoded either as absolute 32-bit addresses, or as a
7-bit or 15-bit 2’s complement value relative to the previous bus analyzer
address.
Address offsets are calculated as [NEW_ADDRESS - PREVIOUSLY_SENT_ADDRESS]. As
shown in Figure 5, bit-7 of the first byte is used to indicate whether a second byte
follows.
Absolute or relative encoding of an address is indicated by one of the following
header fields:
• PC_ABSOLUTE
• SRC_ABSOLUTE (in branch trace messages only)
D R A FT
• DEST_ABSOLUTE (in branch trace messages only)
• ADDR_ABSOLUTE (in bus analyzer trace messages only)
When debug software is analyzing trace message information, it uses an absolute
address as the reference for reconstructing the addresses in subsequent trace
messages. The reference message (Section 1.8.6: Timestamping and reference
messages on page 93 and Table 47 on page 133) also contains the absolute PC and
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SH-5 System Architecture, Volume 3: Debug 05-SA-10003 v1.0