Intel E3815 FH8065301567411 Data Sheet
Product codes
FH8065301567411
PCU – iLB – 8254 Timers
Intel
®
Atom™ Processor E3800 Product Family
4554
Datasheet
37.3.2.1
Simple Read
The first method is to perform a simple read operation. The counter is selected through
Port 40h (Counter 0), 41h (Counter 1), or 42h (Counter 2).
Port 40h (Counter 0), 41h (Counter 1), or 42h (Counter 2).
Note:
Performing a direct read from the counter does not return a determinate value,
because the counting process is asynchronous to read operations. However, in the case
of Counter 2, the count can be stopped by writing 0b to the NSC.TC2E register bit.
because the counting process is asynchronous to read operations. However, in the case
of Counter 2, the count can be stopped by writing 0b to the NSC.TC2E register bit.
37.3.2.2
Counter Latch Command
The Counter Latch command, written to Port 43h, latches the count of a specific
counter at the time the command is received. This command is used to ensure that the
count read from the counter is accurate, particularly when reading a two-byte count.
The count value is then read from each counter’s Count register as was programmed by
the Control register.
counter at the time the command is received. This command is used to ensure that the
count read from the counter is accurate, particularly when reading a two-byte count.
The count value is then read from each counter’s Count register as was programmed by
the Control register.
The count is held in the latch until it is read or the counter is reprogrammed. The count
is then unlatched. This allows reading the contents of the counters on the fly without
affecting counting in progress. Multiple Counter Latch Commands may be used to latch
more than one counter. Counter Latch commands do not affect the programmed mode
of the counter in any way.
is then unlatched. This allows reading the contents of the counters on the fly without
affecting counting in progress. Multiple Counter Latch Commands may be used to latch
more than one counter. Counter Latch commands do not affect the programmed mode
of the counter in any way.
If a counter is latched and then, some time later, latched again before the count is
read, the second Counter Latch command is ignored. The count read is the count at the
time the first Counter Latch command was issued.
read, the second Counter Latch command is ignored. The count read is the count at the
time the first Counter Latch command was issued.
37.3.2.3
Read Back Command
The Read Back command, written to Port 43h, latches the count value, programmed
mode, and current states of the OUT pin and Null Count flag of the selected counter or
counters. The value of the counter and its status may then be read by I/O access to the
counter address.
mode, and current states of the OUT pin and Null Count flag of the selected counter or
counters. The value of the counter and its status may then be read by I/O access to the
counter address.
The Read Back command may be used to latch multiple counter outputs at one time.
This single command is functionally equivalent to several counter latch commands, one
for each counter latched. Each counter's latched count is held until it is read or
reprogrammed. Once read, a counter is unlatched. The other counters remain latched
until they are read. If multiple count Read Back commands are issued to the same
counter without reading the count, all but the first are ignored.
This single command is functionally equivalent to several counter latch commands, one
for each counter latched. Each counter's latched count is held until it is read or
reprogrammed. Once read, a counter is unlatched. The other counters remain latched
until they are read. If multiple count Read Back commands are issued to the same
counter without reading the count, all but the first are ignored.
The Read Back command may additionally be used to latch status information of
selected counters. The status of a counter is accessed by a read from that counter's I/
O port address. If multiple counter status latch operations are performed without
reading the status, all but the first are ignored.
selected counters. The status of a counter is accessed by a read from that counter's I/
O port address. If multiple counter status latch operations are performed without
reading the status, all but the first are ignored.
Both count and status of the selected counters may be latched simultaneously. This is
functionally the same as issuing two consecutive, separate Read Back commands. If
multiple count and/or status Read Back commands are issued to the same counters
without any intervening reads, all but the first are ignored.
functionally the same as issuing two consecutive, separate Read Back commands. If
multiple count and/or status Read Back commands are issued to the same counters
without any intervening reads, all but the first are ignored.