temperature control feature is at boot prom level, (OpenBoot 3.x), in boot prom (OBP):
enable-environmental-monitor
usage: enable-environmental-monitor ( -- )
Purpose: To start monitoring power supply status, board temperatures and board hot plug while the screen displays the ok prompt, this is enabled by default.
Messages Indicating Environmental Conditions
PROM NOTICE: Overtemp detected on board <n.
PROM NOTICE: System has cooled down.
PROM WARNING: Board <n is too hot.
PROM NOTICE: Insufficient power detected.
PROM NOTICE: Power supply restored.
PROM NOTICE: Board insert detected.
PROM NOTICE: Reset Initiated...
Hope this helps,
Carlos Almeida,