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Debugging code on an embedded system is a difficult problem. The basic features of embedded environments – isolation, limited code space – usually preclude having a fully implemented shell with the entire development tool chain present on the dedicated processor. Many commercial vendors (VxWorks, Xilinx) include remote debuggers usable over various connection protocols, but for RTEMS, there wasn't a good way to run debuggers on a large cluster of embedded processors. In this document we discuss the two debugging options we have available for dealing with RCEs: XMD and The GDB stub.
Xilinx Microprocessor Debugger (xmd)
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XMD (Xilinx Microprocessor Debugger) is a low-level (assembly language) debugger that is provided by Xilinx as part of a product called the Embedded Development Kit (EDK). Documentation is in the Embedded System Tools Reference Manual (UG111). XMD communicates with the PowerPC System-On-Chip over a JTAG interface via a host computer's USB system. The secret of a large portion of this magic is that it is able to inject instructions into the processor over JTAG (interestingly, these instructions can be recorded to text files and disassembled with some effort). XMD and the EDK is installed on SLAC AFS (e.g., /afs/slac/g/reseng/xilinx).
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