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Thu Aug 16 17:47:40 EDT 2018

So CPU works

Next: don't use it!

Seriously though, there is a middle ground here: generating state
machines from static programs.

Here's the outline of a practical program I need to write.  The
input/output are abstracted, but essentially they perform two kinds of
actions:

- write to a register
- send a start pulse
- wait for a done pulse

e.g.

- write
- wait
- n times:
  - m times:
    - write
    - wait
- wait
- n times
  - write, pulse
  - wait
  - pulse
  - wait


The essence of this structure is the nesting.
To flatten this requires flattening out the nesting.

What makes a CPU interesting is that it can do loops
A stack then adds nested loops

To translate all that into a state machine requires state for each
level + possibly repurposing the state for the next loop.


I don't even have to work this out to know that the CPU approach is
_much_ simpler once there is any form of nesting.

Note that a UART already performs nesting:
- top level states:  idle->start->data->stop->idle
- inside data there are N data states

So to create a UART, one could also just create a CPU.

Let's look at that in the next post.



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