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

PRELIMINARY DATA
228 DBUS protocol
Mask (msk)
This field appears in request transactions, and is used to define which bytes within
the data field are significant.
Note:
For load requests the DBUS protocol only transfers a single 8-bit msk value, which is
used for the series of underlying 8-byte load operations.
The address of individual bytes within the data field is determined by the msk
value, and the relationship between these values varies according to the endian
mode of the SH-5 system. This is described in Section 3.6.6: Endian-specific
behavior on page 230.
TID (tid, r_tid)
Transaction identifier. When generating a response, R_TID must match the TID value
of the original request.
Dummy
Dummy bits which are included in order to pad the packet to certain alignment and
size constraints. Any value can be supplied for the dummy bits.
3.6.2 Nibble order
For SH-5 implementations using a 4-bit-wide output data port (DM_OUT[0,3]), the
least-significant nibble of each byte is transmitted first, that is, BYTE-I[0,3] followed
by BYTE-I[4,7]. See Table 73: DBUS Load8 request message example on page 210 for
more details.
3.6.3 Pipelining of DBUS requests
D R A FT
The SHdebug link does not support pipelined DBUS requests. The debug module
will accept only a single SuperHyway request addressed to the SHdebug link and
will forward this over the SHdebug link as a DBUS message. When the DBUS
response is received by the debug module from the tool, it is forwarded to
SuperHyway. Only then will the debug module accept another SuperHyway request
addressed to the SHdebug link.
SuperH, Inc.
SH-5 System Architecture, Volume 3: Debug 05-SA-10003 v1.0