add project description

README.md

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 ![](../../workflows/gds/badge.svg) ![](../../workflows/docs/badge.svg) ![](../../workflows/test/badge.svg)
 
+# Project Description
+This project is a rather simplified 4-bit ALU inspired by the 2022 Supercon Badge.
+The challenge was to do this within the constraints of the Tiny Tapeout submission.
+
+A typical 4-bit ALU needs 12 pins just to handle the two input ports and an output port.
+Additional pins would be needed for control. It might also have outputs for a carry-out
+and a zero-detect. So it's easy to imagine a need for at least 10 inputs (assuming 2 input pins to control the ALU mode)
+and 6 outputs (assuming an ALU result, carry-out, and a zero-detect).
+
+Tiny Tapeout (TT02) is limited to 8 inputs and 8 outputs!
+
+To work around these constraints, we surround the ALU with some registers.
+There is an A register and a B register for the A and B inputs of the ALU.
+There is also a Mode register to set the ALU mode (i.e. add or subtract).
+We then add a state machine to allow selectively loading those registers.
+However, the output of the ALU goes directly to the chip-designated outputs.
+
+Currently, only two ALU operations are supported, ADD and SUB.
+
+That's it!
+
+=====
+
 # What is Tiny Tapeout?
 
 TinyTapeout is an educational project that aims to make it easier and cheaper than ever to get your digital designs manufactured on a real chip!