Every FPGA project needs to start with a very simple core. Then, working from
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simplicity, more and more complex cores can be built until an eventual
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application comes from all the tiny details.
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This real time clock began with one such simple core. All of the pieces to
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this clock are simple. Nothing is inherently complex. However, placing this
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clock into a larger FPGA structure requires a Wishbone bus, and being able
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to command and control an FPGA over a wishbone bus is an achievement in and
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of itself. Further, the clock produces outputs that can be used to strobe
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an interrupt line. Reading and processing that interrupt line requires
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a whole 'nother bit of logic and the ability to capture, recognize, and
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respond to interrupts. Hence, once you get a simple clock working, you have
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a lot working.
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Included in this repository are several basic cores which can be
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used for this purpose:
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- rtcclock: the original RTC Clock module. This was originally built for a Basys-3 board, and so it also has outputs suitable for commanding LEDs and a seven segment display.
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- rtclight: Just the basic RTC, with no LEDs or seven segment display output wires.
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- rtcgps: A real-time clock which can be used together with a cleaned-up GPS PPS, to keep the clock accurate at a subsecond level to the top of the second. Further work is required to get the clock to the correct second, but this will hold it to the correct subsecond interval.
