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[/] [zipcpu/] [trunk/] [rtl/] [zipsystem.v] - Rev 18

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18 A couple of changes: Registers can now be changed via the debug interface.
Also, in anticipation of being able to interrupt the break the processor,
the CPU now exports an interrupt line to the external environment to tell
when it has been halted. Thus, if it gets halted by a break instruction,
the ZipSystem will interrupt whatever's in its environment so that the
debugger can come and examine its state.

Oh, and one other: because you can't examine the state of the CPU without
halting it, I modified the debug control register to export the four
useful flags: break-enable, interrupts enabled, and sleep (step comes for
free in this implementation).		 dgisselq 3415d 12h /zipcpu/trunk/rtl/zipsystem.v
11 This version works on an FPGA!!!

(Or at least the wdt.S program passes ...)		 dgisselq 3434d 02h /zipcpu/trunk/rtl/zipsystem.v
9 This checkin is the result of a watchdog timer test, and everything it took
to get the watchdog timer working. The timer function was simplified,
although it now uses a touch more resources--being able to count down 31
bits instead of 30. The parser was modified, since it couldn't handle
storing to register plus offsets like it was supposed to be able to. The
testbench, zippy_tb, was modified to accept an assembled machine code file
such as I might place on a board to test it.

Lots of work to get it working.

Looking at the files below, it looks like I'll need a second check in to check
in the watchdog timer test itself.		 dgisselq 3434d 15h /zipcpu/trunk/rtl/zipsystem.v
3 Rebuilt the pipefetch (instruction fetch/cache module) so that it will
let go of the bus if the memory unit wants it to execute an instruction.
Pipefetch will then grab the bus back whtn the memory unit is done, so things
otherwise continue as they were before.

Other tweaks were made to try to reduce code complexity.		 dgisselq 3434d 23h /zipcpu/trunk/rtl/zipsystem.v
2 An initial load. No promises of what works or not, but this is where the
project is at.		 dgisselq 3435d 16h /zipcpu/trunk/rtl/zipsystem.v

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