startBit, endBit, and bits

[chrisfrederickson]

This issue is for the discussion on startBit, endBit, and bits as it keeps coming up. The key questions to answer are:

1. Should the ordering of startBit and endBit matter? Should we enforce that startBit > endBit or the other way around? Should we support both options? https://github.com/google/cyanobyte/pull/38/files#r271088948
2. If startBit == endBit, should we add the option to use bit? Pimoroni TrackBall breakout description #56

[Fleker]

Using the phrase "start" and "end" could be conflated in some environments, so it may be a good idea to see if it's possible to handle either direction. Additionally, we don't have a good way to enforce this at the specification level through a schema file.

I do like the simplification of bit to indicate a single-bit field.

[Fleker]

On https://arm-software.github.io/CMSIS_5/SVD/html/elem_registers.html, under the topic /device/peripherals/peripheral/registers/.../fields/field element, CMSIS has several styles:

• bitOffset (LSB) and bitWidth
• lsb and msb
• bitRange - A string in the format "[:]"