So far as I can tell, ever since the first version of the ACIA emulation in
Symon, writing 0x00 to the control register has been interpreted as a request
to reset, rather than to actually set the control register to 0x00. This is
strange for a number of reasons:
- All-zeros is actually a very sensible value for the control register, and
is in fact the hardware-reset default.
- I can't find any description of such behaviour in the 6551, W65C51S, or
W65C51N data sheets.
- The 6551 already has a way to trigger "program reset" by writing to the
status register.
So I've removed that quirk, and writing to the control register now just
writes to the control register and nothing else.
The only description of the effects of "program reset" in the original MOS
datasheet is in the section for each register. The W65C51S and W65C51N
datasheets have a heading "PROGRAM RESET OPERATION", but it amounts to:
- internal registers are modified as described in the section for each register
- changes to the DTR, DCD, and DSR pins which Symon does not emulate
- the overrun flag is cleared
...which is what this new implementation does.
It would make *sense* for the reset to do things like "cancel transmission or
reception in progress" and stop asserting an interrupt, as the old code did,
but I can't find any evidence of such behaviour in the datasheets.
- IR field in status panel now correctly displays the next instruction
to be executed, instead of the instruction that was just executed.
- Switched from built-in Java util logger to Logback
- Updated all copyright strings to 2016
Tim Allen