Open Core Protocol Debug Interface Specification rev 1.0 - OCP-IP

OCP-IP Confidential
Figure A.4 Break Switch Interfaces
A.4.5 JTAG Interface
The JTAG interface is a standardized unit that is typically used for boundary scan and internal
device tests. Because both of these applications are not active during normal device operation
in a system, the JTAG port can be used during normal device operation as an ideal interface for
debugging tasks.
On the other hand, the MCDS is designed to support complex multicore/debugging
environments. The challenge here is that several debugger applications may have to share a
single resource, i.e. the same JTAG interface. This becomes even more complicated because
the JTAG module contains the IEEE 1149.1 JTAG state machine, which must be handled in the
correct manner.
The solution to this problem is a JTAG driver with a defined API and a Debug Applications
Server DAS. The server can connect to many debuggers and redirect the debug streams through
one JTAG. It allows several debugger applications to share the same JTAG interface. In
addition, the tool-specific PC interfaces like Ethernet, printer-port, or even USB can be hidden
from the debugger software by the Debug Applications Server DAS.
DAS enables the debugger vendor to ignore the complex task of understanding the JTAG
module and supporting its functionality at low-level. All required information is provided as
specifications and function references. The DAS API can be obtained from the SPRINT
consortium.
A.4.6 Cerberus Bus Master Registers and JTAG
This section summarizes all Cerberus and JTAG registers as seen by the Debug Applications
Server DAS for reference purposes.
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