Here are the data structures with brief descriptions:

HPET_GENERAL_CAPABILITIES_ID_REGISTER
HPET_GENERAL_CONFIGURATION_REGISTER
HPET_TIMER_CONFIGURATION_REGISTER
HPET_TIMER_MSI_ROUTE_REGISTER
IO_APIC_IDENTIFICATION_REGISTER
IO_APIC_REDIRECTION_TABLE_ENTRY
IO_APIC_VERSION_REGISTER