Embedded Development: Tales from the TrenchesReflections on Embedded SystemsHomeAboutDebugging TechniquesPosted on January 29, 2019January 29, 2019 by jerryIf you write perfect code that runs the first time (and every time), move along—there’s nothing to see here. These are not the droids you’re looking for. For the rest of us, who spend at least some of our time debugging embedded code, I’ll offer some of the debugging techniques I’ve found effective over the years.First, some history. When I first started doing embeddeddevelopment in the 1980s, development tools were primitive compared to what wehave today. Yes, there were professional-level development systems, like theIntel Intellec 8 for the 8080A, but these systems tended to be expensive andsmall companies (like the ones I worked for in this era) couldn’t afford them.The next step in the evolution of embedded debugging was theICE, or In-Circuit Emulator. Early ICEs were big, standalone units made bycompanies like Hewlett-Packard and later units were interfaces between a PC andan embedded system. They consisted of a hardware interface that typically useda bond-out version of the embedded microprocessor. These were specialmicroprocessors with debug and bus signals brought out to unused pins and wereused by the ICE to control the micro in the target circuit. Installing oneinvolved removing the micro from its socket in the test system and replacing itwith the bond-out micro, which was in turn connected to the ICE via a ribboncable.  ICEs took complete total controlof the target micro and supported loading code, breakpoints, single-stepping,and displaying CPU registers and memory.My one and only experience with a true ICE was an HP-64243Afor the Motorola 68000. List price back in the day (circa 1984) was around$25,000. My company couldn’t that, so they rented one for a few months while Idebugged the system (an SMD disk controller for the VMEbus). Although HP had aC compiler for that beast (for money, of course), I did all of my work for thatproject in 68K assembly.Modern microcontrollers integrate most of the functionalityof an ICE directly on the die, so it’s no longer necessary to swap the part outfor a bond-out version. All of the debug circuitry is built into the micro anduses four pins to talk to the outside world over a JTAG interface. The JTAGinterface is a small gadget with a cable that connects to a JTAG header on thedevelopment board and a USB cable that connects to a PC.There are many proprietary, third-party, and open sourceversions of the JTAG hardware and interface software available. Too many, infact, to go into details here—perhaps I’ll do a blog post on this subject inthe future. To cut to the chase, you need a target adapter and interfacesoftware compatible with it. Most commercial JTAG target adapters provideinterface software with their hardware that works with most of the populardevelopment tools (Keil, IAR, Eclipse, etc). Some microcontroller vendors (suchas Infineon, ST, a