By Reinhard Keil, ARM Ltd.Embedded.com (07/22/08, 12:15:00 AM EDT)
Before the introduction of on-chip debugging, most software developers were using expensive In-Circuit Emulators (ICE) for application testing on microcontrollers.High-end emulators were connected via complex adapters, and offered also extensive instruction and data trace capabilities with complex triggers.
These emulators were based on special bond-out devices that were different from the standard production devices and therefore very expensive compared to the actual MCU device.
Modern microcontrollers run at high clock rates and come in tiny, high-pin count packages making traditional ICE technology impossible to adapt. Today's microcontrollers offer on-chip debug logic that gives controlled access to memory, CPU registers, and program execution.
This on-chip debug logic is part of every production device and, to avoid extra chip costs, is limited in complexity. Since it is mostly accessed using a standard JTAG interface, the additional bandwidth required for instruction trace is not available.
Most on-chip debug implementations provide only simple run-control debugging with limited breakpoint features. Cortex-M3 processor-based microcontrollers, however, integrate ARM CoreSight debug technology that provides useful trace information via a standard JTAG connector and without the need for costly hardware.
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