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16-38 Vol. 3
DEBUGGING, PROFILING BRANCHES AND TIME-STAMP COUNTER
• BTS (branch trace store) flag (bit 3) — When set, enables the BTS facilities to
log BTMs to a memory-resident BTS buffer that is part of the DS save area. See
Section 16.4.9, “BTS and DS Save Area.”
• BTINT (branch trace interrupt) flag (bits 4) — When set, the BTS facilities
generate an interrupt when the BTS buffer is full. When clear, BTMs are logged to
the BTS buffer in a circular fashion. See Section 16.4.5, “Branch Trace Store (BTS).”
• BTS_OFF_OS (disable ring 0 branch trace store) flag (bit 5) — When set,
enables the BTS facilities to skip sending/logging CPL_0 BTMs to the memory-
resident BTS buffer. See Section 16.7.2, “LBR Stack for Processors Based on Intel
NetBurst Microarchitecture.”
• BTS_OFF_USR (disable ring 0 branch trace store) flag (bit 6) — When set,
enables the BTS facilities to skip sending/logging non-CPL_0 BTMs to the
memory-resident BTS buffer. See Section 16.7.2, “LBR Stack for Processors
Based on Intel NetBurst Microarchitecture.”
The initial implementation of BTS_OFF_USR and BTS_OFF_OS in
MSR_DEBUGCTLA is shown in Figure 16-12. The BTS_OFF_USR and
BTS_OFF_OS fields may be implemented on other model-specific
debug control register at different locations.
See Appendix B, “Model-Specific Registers (MSRs),” for a detailed description of each
of the last branch recording MSRs.
16.7.2 LBR Stack for Processors Based on Intel NetBurst
Microarchitecture
The LBR stack is made up of LBR MSRs that are treated by the processor as a circular
stack. The TOS pointer (MSR_LASTBRANCH_TOS MSR) points to the LBR MSR (or
Figure 16-12. MSR_DEBUGCTLA MSR for Pentium 4 and Intel Xeon Processors
31
TR — Trace messages enable
BTINT — Branch trace interrupt
BTF — Single-step on branches
LBR — Last branch/interrupt/exception
543
2
1
0
BTS — Branch trace store
Reserved
6
7
BTS_OFF_OS — Disable storing CPL_0 BTS
BTS_OFF_USR — Disable storing non-CPL_0 BTS