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[/] [open8_urisc/] [trunk/] [VHDL/] [o8_epoch_timer.vhd] - Rev 244

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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 1628d 08h /open8_urisc/trunk/VHDL/o8_epoch_timer.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 1662d 15h /open8_urisc/trunk/VHDL/o8_epoch_timer.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 1663d 08h /open8_urisc/trunk/VHDL/o8_epoch_timer.vhd
222 Created a modified version of the epoch timer with a 32-bit, 1-uS resolution timer/comparator. jshamlet 1663d 14h /open8_urisc/trunk/VHDL/o8_epoch_timer.vhd
217 Broke out the vdsm8 as a separate entity, since it is used in several places,
Even MORE code cleanup.		 jshamlet 1664d 09h /open8_urisc/trunk/VHDL/o8_epoch_timer.vhd
213 Code and comment cleanup jshamlet 1668d 10h /open8_urisc/trunk/VHDL/o8_epoch_timer.vhd
212 Fixed issue with rewritten epoch timer not clearing alarm on set point write. jshamlet 1668d 16h /open8_urisc/trunk/VHDL/o8_epoch_timer.vhd
209 Fixed an issue in the PIT timer that caused an immediate interrupt on interval write,
Fixed an issue in the epoch timer that resulted in a spurious interrupt due to extra LSB's being set by default in the set point register,
While cleaning elsewhere, founding a spacing issue in the CPU HDL,
Added a 4k ROM and MW core.		 jshamlet 1670d 05h /open8_urisc/trunk/VHDL/o8_epoch_timer.vhd
194 Cleaned up licensing sections jshamlet 1678d 11h /open8_urisc/trunk/VHDL/o8_epoch_timer.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 1678d 11h /open8_urisc/trunk/VHDL/o8_epoch_timer.vhd
189 Merged changes from private repository,
added ceil_log2 function to Open8_pkg, since it is used to calculate RAM vectors,
cleaned up comments and removed local copies of the ceil_log2 function from peripherals.		 jshamlet 1691d 10h /open8_urisc/trunk/VHDL/o8_epoch_timer.vhd
184 More file/entity renaming to match private versions. jshamlet 1698d 11h /open8_urisc/trunk/VHDL/o8_epoch_timer.vhd
173 Added a couple of useful interfaces for detecting button presses and clock changes. jshamlet 3223d 09h /open8_urisc/trunk/VHDL/o8_etc.vhd
172 General code cleanup jshamlet 3223d 09h /open8_urisc/trunk/VHDL/o8_etc.vhd
171 Fixed comments for offsets 0x0 - 0x3 to indicate the read value jshamlet 3223d 09h /open8_urisc/trunk/VHDL/o8_etc.vhd
170 Added 24-bit resolution epoch timer / alarm clock jshamlet 3223d 09h /open8_urisc/trunk/VHDL/o8_etc.vhd

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