SAMD21J datasheet(28/59 Pages) MICROCHIP

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Peripheral Source

NVIC Line

AC – Analog Comparator

DAC – Digital-to-Analog Converter

PTC – Peripheral Touch Controller

I2S - Inter IC Sound

7.3

Micro Trace Buffer

7.3.1

Features

•

Program flow tracing for the Cortex-M0+ processor

•

MTB SRAM can be used for both trace and general purpose storage by the processor

•

The position and size of the trace buffer in SRAM is configurable by software

•

CoreSight compliant

7.3.2

Overview

When enabled, the MTB records changes in program flow, reported by the Cortex-M0+ processor over

the execution trace interface shared between the Cortex-M0+ processor and the CoreSight MTB-M0+.

This information is stored as trace packets in the SRAM by the MTB. An off-chip debugger can extract the

trace information using the Debug Access Port to read the trace information from the SRAM. The

debugger can then reconstruct the program flow from this information.

The MTB simultaneously stores trace information into the SRAM, and gives the processor access to the

SRAM. The MTB ensures that trace write accesses have priority over processor accesses.

The execution trace packet consists of a pair of 32-bit words that the MTB generates when it detects the

processor PC value changes non-sequentially. A non-sequential PC change can occur during branch

instructions or during exception entry. See the CoreSight MTB-M0+ Technical Reference Manual for more

details on the MTB execution trace packet format.

Tracing is enabled when the MASTER.EN bit in the Master Trace Control Register is 1. There are various

ways to set the bit to 1 to start tracing, or to 0 to stop tracing. See the CoreSight Cortex-M0+ Technical

Reference Manual for more details on the Trace start and stop and for a detailed description of the MTB’s

MASTER register. The MTB can be programmed to stop tracing automatically when the memory fills to a

specified watermark level or to start or stop tracing by writing directly to the MASTER.EN bit. If the

watermark mechanism is not being used and the trace buffer overflows, then the buffer wraps around

overwriting previous trace packets.

The base address of the MTB registers is 0x41006000; this address is also written in the CoreSight ROM

Table. The offset of each register from the base address is fixed and as defined by the CoreSight MTB-

M0+ Technical Reference Manual. The MTB has 4 programmable registers to control the behavior of the

trace features:

•

POSITION: Contains the trace write pointer and the wrap bit,

•

MASTER: Contains the main trace enable bit and other trace control fields,

•

FLOW: Contains the WATERMARK address and the AUTOSTOP and AUTOHALT control bits,

•

BASE: Indicates where the SRAM is located in the processor memory map. This register is

provided to enable auto discovery of the MTB SRAM location, by a debug agent.

See the CoreSight MTB-M0+ Technical Reference Manual for a detailed description of these registers.

32-bit ARM-Based Microcontrollers

Datasheet Summary

40001884A-page 28

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