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XC161-32 Derivatives
System Units (Vol. 1 of 2)
Debug System
The access to any memory location is performed with injected instructions, as PEC
transfer. The following Cerberus IO Instructions can be used in their generic meaning:
•
•
•
IO_READ_WORD, IO_WRITE_WORD
IO_READ_BLOCK, IO_WRITE_BLOCK
IO_WRITE_BYTE
Within these instructions, the host writes/reads data to/from a dedicated
register/memory, while the Cerberus itself takes care of the rest: to perform a PEC
transfer by injection of the appropriate instructions to the Core.
Communication Mode of Operation
In this mode the external host (debugger) communicates with a program (Monitor)
running on the CPU. The data-transfers are made via a PDBus+ register. The external
host is master of all transactions, requesting the monitor to write or read a value.
The difference to Read/Write Mode of Operation is that the read or write request now
is not actively executed by the Cerberus, but it sets request bits in a CPU accessible
register to signal the Monitor, that the host wants to send (IO_WRITE_WORD) or receive
(IO_READ_WORD) a value. The Monitor has to poll this status register and perform
respectively the proper actions
Communication Mode is the default mode after reset. Only the IO_WRITE_WORD and
IO_READ_WORD Instructions are effectively used in Communication Mode.
The Host and the Monitor exchange data directly with the dedicated data-register. For a
synchronization of Host (Debugger) and Monitor accesses, there are associated control
bits in a Cerberus status register.
User’s Manual
OCDS_X83, V2.1
11-8
V1.0, 2004-02