Khz Timer - Texas Instruments OMAP5910 Technical Reference Manual

32-kHz Timer

7.5 32-kHz Timer
7.5.1 Operating System Scalable Clock-Tick Interrupt Function
7-46
The MPU subsystem operating system (OS) requires interrupts at regular time
intervals for OS scheduling purpose. OS time intervals can be from 1 ms to
30 ms. These time intervals can be generated using the three 32-bit OS/gener-
al-purpose TI925T timers, which use CLKIN or DPLL1; however, they can not
be used when the system clock is not operating. Therefore, a 32-kHz clock-
based timer is needed to provide the required OS timing interval. The clock
period of 32 kHz is 30.60 µs. 32 kHz refers to 32678, not 32000.
A programmable interval timer is required to generate a periodic interrupt, also
called system clock tick, to the OS. This is used to keep track of the current
time to control the operation of device drivers.
For example, Microsoft Windows CE OS scheduling requires the following:
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The periodic interrupt occurs every 1-25 ms.
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The timer is expected to run in all modes except when suspended.
32-kHz timer is a 24-bit down-counter that generates CPU interrupts for the
TI925T processor. The following capabilities are available:
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Timer reset
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Timer current value reading
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Timer start and stop
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Interrupt generation as timer down-counts to zero
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Timer autorestart after it counts to zero
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On-the-fly register read and write
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Interrupt disabling the by writing a 1 to the interrupt bit in the control
register
Timer Corresponding Level 2 Interrupt
32-kHz timer
IRQ_22
The tick value register (TVR) contains the desired value for the timer to count
down. The tick counter register (TCR) is loaded with this value, then starts to
count down to zero and generates a negative edge sensitive interrupt
(low-level pulse duration = 15 µs) to the interrupt handler. Once the interrupt
is back to the high level, the counter is reloaded from its register and then starts
to count down again.