IDT EJTAG System
EJTAG Processor Core Extensions
79RC32438 User Reference Manual
20 - 9
November 4, 2002
Notes
The SYNC instruction, followed by appropriate spacing (as described in section “SYNC Instruction
Behavior” on page 20-11 and section “CP0 and dseg Hazards” on page 20-12) must be executed to ensure
that an access to dseg is committed (for example, after writing to dseg and before leaving Debug Mode).
This procedure ensures that locations in dseg are fully updated for Non-Debug Mode, otherwise behavior of
the processor is UNDEFINED.
Access to dmseg (EJTAG memory) Address Range
Table 20.8 shows the behavior of processor accesses in Debug Mode to the dmseg address range from
0xFF20 0000 to 0xFF2F FFFF.
Note:
When ProbEn equals 0 for dmseg accesses, debug software accessed dmseg when the
ProbEn bit was 0, indicating that there is no probe available to service the request. Debug
software must read the state of the ProbEn bit in the DCR register before attempting to reference
dmseg. However, accessing dmseg while ProbEn is 0 can occur because there is an inherent
race between the debug software sampling the ProbEn bit as 1 and the probe clearing it to 0. The
probe can therefore not assume that a reference to dmseg never occurs if the ProbEn bit is
dynamically cleared to 0. If debug software references dmseg when ProbEn is 0, the reference
hangs until it is satisfied by the probe.
Segment
Name
Subseg-
ment
Name
Virtual
Address
Reference Address
Cache
Attribute
dseg
dmsg
0xFF20 0000
to
0xFF2F FFFF
Because the dseg address range is serviced
exclusively by the EJTAG features, there are
no physical address per se. Instead the lower
21 bits of the virtual address select the
appropriate reference in either EJTAG mem-
ory or registers.
References are not mapped through the TLB,
nor do the accesses appear on the external
system memory interface.
Uncached
dreg
0xFF30 0000
to
0xFF3F FFFF
Table 20.7 Physical Address and Cache Attribute for dseg’s dmsg and drseg
NoDCR
bit in
Debug
Register
Trans-
action
ProbEn bit
in DCR
Register
LSNM bit in
Debug
Register
Access
1
x
1
1.
x = don’t care
(Not present)
0 (read only)
Kernel Mode address space
0
Fetch
1
x
dmseg
0
x
See note below table on
ProbEn behavior
Load/Store
1
0
dmseg
1
Kernel Mode address space
0
1
Kernel Mode address space
0
See note below table on
ProbEn behavior
Table 20.8 Access to dmseg Address Range