This PR is the first of two PRs that replaces earlier PRs #2589 and #2590.
Due to a git branching mishap it was decided to re-partition the new
functionality in two sequential PRs that offer self-contained, new
functionality to sim65.
The functionality in this first PR extends the sim65 simulator in the following ways:
(1) It provides tracing functionality, i.e., the possibility of printing one line of simulator state information per instruction executed.
(2) It provides a memory mapped "sim65 control" peripheral that allows control of (a) the tracing functionality, and (b) the cpu mode.
(3) It provides command-line options to sim65 to enable the tracing, and to override the CPU mode as specified in the program file header.
More detailed information and some discussion can be found in the discussions with the (now retracted) PRs #2589 and #2590.
This PR provides the technical infrastructure inside the sim65 simulator program itself. Once this PR is accepted, a follow-up PR will be posted that adds C and assembly-language support for the new tracing and peripheral features so they can be easily accessed from the CC65 compiler and the CA65 assembler; some examples; and the documentation for these features. The lack of the latter, in this pull request, will be addressed then.
The sim65 source code has been a construction site for over a decade.
I was looking for a simple cc65 program execution environment for
regression tests. So I decided to re-purpose sim65 for that task by
removing about everything but the 6502 emulation.
There's no memory mapped i/o emulation whatsoever. Rather exit(),
open(), close(), read() and write() calls are supported by mapping
them through a thin paravirtualization layer to the corresponding
host os functions.
Note: The sim65 6502 emulation provides means to switch between
6502 and 65C02 emulation but currently there are no actual 65C02
opcodes implemented.
