
180
Registers
Chapter 4
AMD-8111 HyperTransport I/O Hub Data Sheet
24674
Rev. 3.00
April 2003
AMD Preliminary Information
HPE Timer 0 Compare Register
HPET108
Default:
0000_0000_FFFF_FFFFh
Attribute:
See below.
3
T0PEN. Timer 0 Periodic Mode Enable
. Read-write. If T0PCAP is 0. this bit is always 0. Writes have
no effect. If T0PCAP is 1, this bits enables the period mode of timer 0.
0 = disables timer 0 periodic mode
1 = enables timer 0 periodic mode
T0IEN. Timer 0 Interrupt Enable
. Read-write. This bit must be set to enable timer 0 to cause an
interrupt when it times out. If this bit is 0, the timer can still count and generate the appropriate status
bits, but does not cause an interrupt.
T0ITYPE. Timer 0 Interrupt Type
.Read-write.
0 = The timer interrupt is edge triggered. Each new interrupt generates a new edge.
1 = The timer interrupt is level triggered. The interrupt is held active until the corresponding bit in the
HPET20[C0_STS] register is cleared. If a new interrupt occurs before the interrupt is cleared, the
interrupt remains active.
Reserved. Read-only. Hardwired to 0. Software should only write a 0 to this bit.
2
1
0
Bits
63:32 Reserved. Read-only. These bits are hardwired to 0000_0000h.
31:0
T0COMP. Timer 0 Comparator Value
.Read-write.
In non-periodic mode (HPET100[T0PEN]=0) a write to this register sets the comparator value. Reads
to this register return the value of the comparator. When the main counter equals T0COMP the
corresponding interrupt is generated, if enabled. The value in this register does not change based on
the generated interrupt.
In periodic mode (HPET100[T0PEN]=1) this register consists of two registers, one for saving the last
software-written comparator value and one for the accumulator value. If HPET100[SETVAL] is High a
write to this address causes a write of this accumulator register, if HPET100[SETVAL] is Low a write to
this address causes a change of the last software-written comparator value. The read value is the
value of the accumulator register. When the main counter equals the accumulator register value, the
last software-written comparator value is added to the accumulator, and the corresponding interrupt is
generated, if enabled.
Description
Bits
Description (Continued)