Debugging aids for systems-on-a-chip

Abstract

The advent of in-circuit emulation (ICE) tools to the embedded systems designer was akin to the advent of the tractor to farmers: life suddenly became easier. The ICE allows easy access to the CPU register set, memory map and allows simple implementation of features such as hardware breakpoints and trace functions. Essentially, the ICE allows a target cable from the (ICE) box to be directly connected, via a header-socket interface, to the circuit board. The header consists of an exact representation of the microcontroller footprint. As microcontrollers are becoming more highly integrated however, the ICE solution in itself is facing certain challenges. Firstly, microcontroller bus speeds are increasing rapidly, roughly doubling every 4-5 years. This presents a problem as high clock rates are difficult to emulate using a cable and target connector. In addition, address and data-bus ports aren't always available on single chip MCUs, thus memory replacement hardware and logic analyzer approaches can be restricted. Another problem which the ICE cannot resolve is that of the mechanical interface. As MCU pincounts increase (at a rate similar to their clock speeds), 'hookover' connectors are becoming increasingly unreliable, unmanageable and downright expensive. In many applications, the space restrictions placed on the control unit (where the circuit resides) will simply not permit a hookover connection. This physical size limitation in fact, is fast becoming very common.