TC1796
System Units (Vol. 1 of 2)
On-Chip Debug Support
User’s Manual 17-12 V2.0, 2007-07
OCDS, V2.0
17.4 Debug Interface (Cerberus)
The Cerberus module is the on-chip unit that controls all OCDS Level 1 and 2 main
debug functions. Generally, the Cerberus should not be used by any application
software, since this could disturb the emulation tool behavior.
The Cerberus module is built up by three parts (see also Figure 17-1):
• OCDS System Control Unit - OSCU
• JTAG Debug Interface - JDI
• Multi Core Break Switch - MCBS
A standard JTAG interface is connected via the JTAG controller with the JDI. Two pins
are available to handle an external break condition. An external debug hardware can
access the Cerberus registers and arbitrary memory locations across the System
Peripheral (FPI) Bus.
Features
• 5-pin standard JTAG interface for OCDS Level 1 control
• Generation of external break condition via pins BRKIN/BRKOUT
• Full access to the complete SPB/RPB (FPI) Bus address space via JTAG
• No user resources (hardware/software) are required
• Minimum run-time impact
• Generic memory read/write functionality
• Write word, half-word and byte
• Block read and write
• Full support for communication between an on-chip monitor program and the
external debugger
• Pending reads/writes can be optionally triggered by the OCDS module (memory
tracing)
• Download of programs and data via JTAG
• Control of the OCDS blocks
• Data acquisition
17.4.1 RW Mode
As the name implies, the RW mode is used by a JTAG host to read or write arbitrary
memory locations via the JTAG interface. The RW mode needs the FPI Bus master
interface of the Cerberus to actively request data reads or data writes.
Data Types Supported
• WORD (32-bit): The default data type; used for single word transfers and block
transfers.
• HWORD (16-bit): For reading 16-bit registers without getting an FPI Bus error, a
dedicated JTAG instruction is provided (IO_READ_HWORD).
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