On a T43p (and at least since T40) this is a Renesas H8S/2161BV, a 16-bit single-chip micro-controller located below the ExpressCard/CardBus slots. It has its own OS in 128 KB flash memory and since this OS is available in the EC updates, it is possible to analyze and modify it. Or we will at least be able to better understand how it can be configured since there doesn't seem to be much documentation available about the EC.
For people willing to delve deeply into H8S assembly language, there is now a set of files that allows to customize the EC of all T4x and some R5x types. This is somewhat risky business and may lead to system board replacement if not done very carefully. However, in a collective effort, it will lead to improvements of the fan issues that some have.
Please take a look at it if interested and share your insights:
- README.txt (assembling instructions)
- 1YHT29WW.html [255 KB] (pretty-printed code, version 1.06 for T43/p 26xx types only; takes some time to load)
- ec.html [274 KB] (pretty-printed code, all versions/types combined; takes quite some time to load and run)
- ec-18s.7z [468 KB] (all code, including above files; self-extracting 7-Zip archive if renamed to ec-18s.exe)
- h8300-coff-as.pdf [520 KB] (GNU As manual)