36-50 Vol. 3C

INTEL® PROCESSOR TRACE

36.4.2.12   Mini Time Counter (MTC) Packet

Table 36-31. MTC Packet Definition

Name

Mini time Counter (MTC) Packet

Packet Format

Dependencies

IA32_RTIT_CTL.MTCEn && 

TriggerEn

Generation 

Scenario

Periodic, based on the core crystal clock, or Always Running Timer 

(ART).

Description

When enabled by software, an MTC packet provides a periodic indication of wall-clock time. The 8-bit CTC (Common 

Timestamp Copy) payload value is set to (ART >> N) & 0xFF. The frequency of the ART is related to the Maximum 

Non-Turbo frequency, and the ratio can be determined from CPUID leaf 15H, as described in Section 36.8.3.

Software can select the threshold N, which determines the MTC frequency by setting the IA32_RTIT_CTL.MTCFreq 

field (see Section 36.2.7.2) to a supported value using the lookup enumerated by CPUID (see Section 36.3.1). 

See Section 36.8.3 for details on how to use the MTC payload to track TSC time.

MTC provides 8 bits from the ART, starting with the bit selected by MTCFreq to dictate the frequency of the packet. 

Whenever that 8-bit range being watched changes, an MTC packet will be sent out with the new value of that 8-bit 

range. This allows the decoder to keep track of how much wall-clock time has elapsed since the last TSC packet was 

sent, by keeping track of how many MTC packets were sent and what their value was. The decoder can infer the 

truncated bits, CTC[N-1:0], are 0 at the time of the MTC packet.

There are cases in which MTC packet can be dropped, due to overflow or other micro-architectural conditions. The 

decoder should be able to recover from such cases by checking the 8-bit payload of the next MTC packet, to deter-

mine how many MTC packets were dropped. It is not expected that >256 consecutive MTC packets should ever be 

dropped.

Application

MTC does not precisely indicate the time of any other packet, nor does it bind to any IP. However, all preceding pack-

ets represent instructions or events that executed before the indicated ART time, and all subsequent packets repre-

sent instructions that executed after, or at the same time as, the ART time.

7

6

5

4

3

2

1

0

0

0

1

0

1

1

0

0

1

1

CTC[N+7:N]