Features - NXP Semiconductors MKL27Z128VFM4 Reference Manual

Introduction
• Destination address field set to bits[31:1] of the EXC_RETURN value. See the
ARM v6-M Architecture Reference Manual.
• The A-bit set to 0.
• The second packet has the:
• Source address field set to bits[31:1] of the EXC_RETURN value.
• Destination address field set to the address of the instruction where execution
commences.
• A-bit set to 1."
Given the recorded change-of-flow trace packets in system RAM and the memory image
of the application, a debugger can read out the data and create an instruction-by-
instruction program trace. In keeping with the low area and power implementation cost
design targets, the MTB trace format is less efficient than other CoreSight trace modules,
for example, the ETM (Embedded Trace Macrocell). Since each branch packet is 8 bytes
in size, a 1 KB block of system RAM can contain 128 branches. Using the Dhrystone 2.1
benchmark's dynamic runtime as an example, this corresponds to about 875 instructions
per KB of trace RAM, or with a zero wait state memory, this corresponds to
approximately 1600 processor cycles per KB. This metric is obviously very sensitive to
the runtime characteristics of the user code.
The MTB_DWT function (not shown in the core platform block diagram) monitors the
processor address and data buses so that configurable watchpoints can be detected to
trigger the appropriate response in the MTB recording.

43.1.2 Features

The key features of the MTB_RAM and MTB_DWT include:
• Memory controller for system RAM and Micro Trace Buffer for program trace
packets
• Read/write capabilities for system RAM accesses, write-only for program trace
packets
• Supports zero wait state response to system bus accesses when no trace data is being
written
• Can buffer two AHB address phases and one data write for system RAM accesses
• Supports 64-bit program trace packets including source and destination instruction
addresses
• Program trace information in RAM available to MCU's application code or external
debugger
• Program trace watchpoint configuration accessible by MCU's application code or
debugger
• Location and size of RAM trace buffer is configured by software
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KL27 Sub-Family Reference Manual , Rev. 5, 01/2016
Freescale Semiconductor, Inc.