Intel E3815 FH8065301567411 Data Sheet
Product codes
FH8065301567411
PCU – iLB – High Precision Event Timer (HPET)
Intel
®
Atom™ Processor E3800 Product Family
4562
Datasheet
38.1.2
Periodic Mode - Timer 0 only
When set up for periodic mode, when the main counter value matches the value in
T0CV, an interrupt is generated (if enabled). Hardware then increases T0CV by the last
value written to T0CV. During run-time, T0CV can be read to find out when the next
periodic interrupt will be generated. Software is expected to remember the last value
written to T0CV.
T0CV, an interrupt is generated (if enabled). Hardware then increases T0CV by the last
value written to T0CV. During run-time, T0CV can be read to find out when the next
periodic interrupt will be generated. Software is expected to remember the last value
written to T0CV.
Example: if the value written to T0CV is 00000123h, then
•
An interrupt will be generated when the main counter reaches 00000123h.
•
T0CV will then be adjusted to 00000246h.
•
Another interrupt will be generated when the main counter reaches 00000246h.
•
T0CV will then be adjusted to 00000369h.
When the incremented value is greater than the maximum value possible for T0CV, the
value will wrap around through 0. For example, if the current value in a 32-bit timer is
FFFF0000h and the last value written to this register is 20000, then after the next
interrupt the value will change to 00010000h.
value will wrap around through 0. For example, if the current value in a 32-bit timer is
FFFF0000h and the last value written to this register is 20000, then after the next
interrupt the value will change to 00010000h.
If software wants to change the periodic rate, it writes a new value to T0CV. When the
timer's comparator matches, the new value is added to derive the next matching point.
If software resets the main counter, the value in the comparator's value register must
also be reset by setting T0C.TVS. To avoid race conditions, this should be done with the
main counter halted. The following usage model is expected:
timer's comparator matches, the new value is added to derive the next matching point.
If software resets the main counter, the value in the comparator's value register must
also be reset by setting T0C.TVS. To avoid race conditions, this should be done with the
main counter halted. The following usage model is expected:
1. Software clears GCFG.EN to prevent any interrupts.
2. Software clears the main counter by writing a value of 00h to it.
3. Software sets T0C.TVS.
4. Software writes the new value in T0CV.
5. Software sets GCFG.EN to enable interrupts.
38.1.2.1
Interrupts
If each timer has a unique interrupt and the timer has been configured for edge-
triggered mode, then there are no specific steps required. If configured to level-
triggered mode, then its interrupt must be cleared by software by writing a '1' back to
the bit position for the interrupt to be cleared.
triggered mode, then there are no specific steps required. If configured to level-
triggered mode, then its interrupt must be cleared by software by writing a '1' back to
the bit position for the interrupt to be cleared.
Interrupts associated with the various timers have several interrupt mapping options.
Software should mask GCFG.LRE when reprogramming HPET interrupt routing to avoid
spurious interrupts.
Software should mask GCFG.LRE when reprogramming HPET interrupt routing to avoid
spurious interrupts.
38.1.2.2
Mapping Option #1: Legacy Option (GCFG.LRE set)
This forces the following mapping: