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[/] [open8_urisc/] [trunk/] [VHDL/] [o8_max7221.vhd] - Rev 335

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244 Added two new generics to the CPU model. The first is a supervisory mode that disables the STP PSR_I instruction. This prevents errant code execution from setting the I bit, and disabling any subsequent memory protection logic. The second allows the default state of the I bit to be set at startup. If set true, initialization code will run with the I bit set, allowing it to bypass memory protection.

Also modified the RAM models to include write mask logic, where the mask register is write-protected by the I bit in the CPU. When enabled, the models will prevent code from writing to memory regions which do not have their mask bits set. The upshot is that code can effectively "write protect" the RAM - which is useful for multitasking applications.

Also, most modules have been updated with write qualification inputs, allowing a similar scheme to be used for I/O, though not as elegantly. I use a register module, whose own write qual line is attached to the external copy of the I bit as an I/O write protect register.

Lastly, added a new externally triggered timer, which can generate pulses with programmable delays and widths, and which can interrupt on either the input trigger, the output rising edge, or output falling edge. The time base can be either the internal microsecond tick signal, or an external clock.		 jshamlet 1655d 14h /open8_urisc/trunk/VHDL/o8_max7221.vhd
224 Finished new Open8 bus record, which now includes the clock, reset and a microsecond tick. The CPU now accepts a clock and pll_locked signal, which it uses to generate the system reset in the bus record. It also contains a simple microsecond counter to feed the usec_tick in the record. This logic was removed from the real time clock and system timer entities, which now use the global version. Bus connections should be dramatically simplified, as only the read logic and interrupts are still run as separate signals. jshamlet 1689d 21h /open8_urisc/trunk/VHDL/o8_max7221.vhd
223 Added an OPEN8_BUS_TYPE record to simplify connection to Open8 modules. The CPU now passes and Open8_Bus out, which supplies the bus address, write enable, write data, and read enable. Read data and interrupts are still handled as separate signals, since they are muxed/connected at the next level up. jshamlet 1690d 14h /open8_urisc/trunk/VHDL/o8_max7221.vhd
217 Broke out the vdsm8 as a separate entity, since it is used in several places,
Even MORE code cleanup.		 jshamlet 1691d 15h /open8_urisc/trunk/VHDL/o8_max7221.vhd
213 Code and comment cleanup jshamlet 1695d 16h /open8_urisc/trunk/VHDL/o8_max7221.vhd
194 Cleaned up licensing sections jshamlet 1705d 16h /open8_urisc/trunk/VHDL/o8_max7221.vhd
191 Cleaned up comments, added back the OPEN8_NULLBUS constant, and added some new modules for ADCs and LCD displays.
Also made the button input module more configurable by moving the debounce code to a separate entity and using generics to instantiate it.		 jshamlet 1705d 17h /open8_urisc/trunk/VHDL/o8_max7221.vhd

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