Reading of 6502/65816 CPU registers by a PC-based debugger
Modern microcontrollers and microprocessors have built-in facilities for external debuggers to read/write registers, set breakpoints and generally fully control the CPU. This is one of the main use cases of the standard JTAG interface. The 6502 and 65816 CPUs were created more than a decade before the first version of JTAG was even defined. They contain no support for external debuggers whatsoever.
Kevin shows how the X65 computer implements the necessary functions for a debugger running on a host PC (with Linux or Windows) and connected over the USB-C port.
Debugger software for X65 is implemented in Python 3 (with the pyftdi module) and it is available in the git repository in subfolder x65pyhost. For simplicity of development, debugger commands are not yet integrated in an IDE but they are available as individual programs called from a command line.
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