|R0||Head number (0-based)|
|R4||Bits 0-23: 15 (reason code)|
|Bits 24-31: Display number|
|R0||0 or error block pointer|
|-||All other registers preserved|
This call is used to switch the display output from one graphics card head to another.
If the call is left unclaimed, the kernel has no HAL-based fallback in place.