GXM Datasheet, PDF (52/244 Pages) National Semiconductor (TI) – Geode™ GXm Processor Integrated x86 Solution with MMX Support

Processor Programming (Continued)
3.3.2.3 Debug Registers
Six debug registers (DR0-DR3, DR6 and DR7) support
debugging on the GXm processor. Memory addresses
loaded in the debug registers, referred to as “breakpoints,”
generate a debug exception when a memory access of
the specified type occurs to the specified address. A
breakpoint can be specified for a particular kind of mem-
ory access such as a read or write operation. Code and
data breakpoints can also be set allowing debug excep-
tions to occur whenever a given data access (read or write
operation) or code access (execute) occurs. The size of
the debug target can be set to 1, 2, or 4 bytes. The debug
registers are accessed through MOV instructions that can
be executed only at privilege level 0 (real mode is always
privilege level 0).
The Debug Address Registers (DR0-DR3) each contain
the linear address for one of four possible breakpoints.
Each breakpoint is further specified by bits in the Debug
Control Register (DR7). For each breakpoint address in
DR0-DR3, there are corresponding fields L, R/W, and
LEN in DR7 that specify the type of memory access asso-
ciated with the breakpoint.
The R/W field can be used to specify instruction execution
as well as data access breakpoints. Instruction execution
breakpoints are always taken before execution of the
instruction that matches the breakpoint. The Debug Reg-
isters are mapped in Table 3-12
Table 3-12. Debug Registers
31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
DR7 Register
Debug Control Register 7 (R/W)
LEN3 R/W3 LEN2 R/W2 LEN1 R/W1 LEN0 R/W0 0 0 G 0 0 1 0 0 G L G L G L G L0
D
3322110
DR6 Register
Debug Status Register 6 (RO)
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 B B 0 1 1 1 1 1 1 1 1 1 B3 B2 B1 B0
TS
DR3 Register‘
Debug Address Register 3 (R/W))
Breakpoint 3 Linear Address
DR2 Register
Debug Address Register 2 (R/W)
Breakpoint 2 Linear Address
DR1 Register
Debug Address Register 1 (R/W)
Breakpoint 1 Linear Address
DR0 Register
Debug Address Register 0 (R/W)
Breakpoint 0 Linear Address
Note: All bits marked as 0 or 1 are reserved and should not be modified.
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