For the impatient
Building up the cell library was important but required patience for the detail. We will next work through the major functional building block of the secure hash function, which will also be detailed. So, let’s cheat a little and take a look ahead at the assembled unit.
Take your time. Run the video slowly, repeatedly, or pause to take a look at each part.
There are 8 bits being processed in that pipe, bits ‘a’ through ‘h’, and the pipe comes in two parts. The first part handles bits e..h, as well as taking message input from the Scheduler part of the SHA-256 algorithm. That is the e-pipe. There is an empty gap where a buffer (amplifier) will go for the e-bit output, and where carry look-ahead may be placed. Then the next section is the a-pipe which handles bits a..d as well as some results of the e-pipe. That also is followed by a gap which will be used for buffers and loo-ahead. Then the next stage of the SHA-256 will begin. Of course, details of why and what are in the upcoming regular posts.
That pipe unit is 0.48 microns wide and 7.4 microns long - roughly 3.7 square microns.
The design is long and narrow so that 32 copies can be fitted side by side with abutting connections. These thirty-two 8-bit pipes form the 256-bit processing of a single stage of SHA-256. There are 64 stages in a SHA-256 and two SHA-256 units concatenated to run the blockchain mining hash, so in total each blockchain hash uses 4096 copies of the pipe in that video.
If this design ran all the blockchain calculations in use now, there would be about 3 quadrillion (3 x 10^15) pipe units in use. Each pipe unit (including a Scheduler part which is not in the video) has about 500 CMOS P/N pairs, so with 15GW average power use by the blockchain today, each pair in the design would be responsible for 30MW of power, about the average electricity use of the USA for 21,000 people, or average of 60,000 typical EVs. For each pair of transistors in this design.
Which is why this is one of the few circuits in the world worth insane attention to detail to ensure it is the most energy efficient it can be.
On Monday ..
We resume the normal flow of posts and dive into those details. Posts go out to paying subscribers on Monday mornings, and to every subscriber on Thursday mornings. Everyone is welcome to comment and make suggestions. Only paid subscribers may comment on the posts with partially restricted content (SubStack makes that rule), but everyone can comment on open posts like this one or the Table of Contents, and you are encouraged to mention which post you may be referring to.