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Evaluating and Programming the 29K RISC Family
os_cold_start
This is the starting address of operating system cold–start code. For processors
which do not use the
dbg_coredump
option it is likely placed at address 0. Addition-
ally, if the processor supports Monitor mode then cold–start code is likely to be
placed at address 24, just after the jump to
dbg_m_trap
. The DebugCore causes
execution to start at the address given by the
os_cold_start
field of the shared
memory structure when a RESET message is received. However, if this field value is
zero then execution continues at linked address label
os_cold_start
.
os_warn
This is the label at the start of OS code dealing with a Warn trap. For processors
without Monitor mode it should be at address 16, otherwise some higher address. The
DebugCore causes execution to start at the address given by the
os_warn
field of the
shared memory structure when the processor warn ipin is activated. However, if this
field value is zero then execution continues at linked address label
os_warn
.
os_V_illop
The DebugCore is given control of the illegal opcode trap by the operating sys-
tem. However, a real illegal opcode trap may occur and the DebugCore must return
control to the OS. This is achieved by entering the OS at address
os_V_illop
supplied
by the shared memory structure. The OS may at this point return control to the De-
bugCore at label
dbg_trap
. If this is done then
gr64
should not be set to zero as this
will cause the DebugCore and OS to enter an endless loop. However, if this field val-
ue is zero then execution continues at linked address label
os_V_illop
.
D.4.2 The Message System 1.0
The message system provides a means by which the operating system and the
DebugCore can communicate with MonTIP and ultimately the DFE. Communica-
tion with MonTIP is via message packets. Each packet has a two 32–bit word header.
The first word specifies the message Class and the second the message Length in by-
tes. Note, the length does not include the 8–bytes of the header. File dbg_core.h de-
fines the AMD reserved message Class numbers (numbers less than 128). Figure D-6
lists the messages received by the DebugCore. There are corresponding messages
sent by the DebugCore.
The operating system uses the message system to request HIF services (for ser-
vice numbers less than 256) and for standard input and output channel data.
Figure D-7 shows the module interconnection symbols. The module interacts
with the DebugCore, the OS and any additional communications module; such as the
serial driver module (SER). When the message system is used with hardware such as
PC plug–in boards, which have shared memory, there is no need for an additional
communications driver module.