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Digital Signal Processing
with DSK6713
EE433Session 12
4th
May 2009
Department of Electrical Engineering
Air University
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Todays Agenda
Introduction to timer / counter
Using the timer on DSP C6713
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Timer / Counter
Most of the embedded systems (microcontrollers, DSPs, etc.)
have built-in timers / counters.
These are hardware modules usually comprised of T flip flops.
These modules can take clock frequency from outside or inside
of the chip.
When clock frequency is fed from outside, it is called
counter.
When the clock is given from inside, it is timer.
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Timer / Counter When you like to run a certain function after a
specific time
interval, you configure this module as timer.
It is very much similar to a timer in a washing machine. You
set
the timer at a value after which you like to stop the
machine
automatically.
If you like to count the number of pulses generated by some
external hardware, you configure the same module as counter
and it counts the number of pulses received at a particular
pin
of the chip.
It is very much similar to the counter in ATM machine. If
you
enter your PIN wrong three times, it captures your card.
There
is a counter inside, that counts your wrong entries for PIN.
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Timer / Counter Apparently a T flip flop behaves as counter. If
you cascade 4 flip
flops you can count from 0 to 15. If 6 flip flops are cascaded
you
can count up to 26 -1 (=63).
Then how a counter becomes a timer when clock is generated
internally?
Its just an interpretation. When the clock is generated
internally you know the frequency.
When you set counter / timer for a certain target value you
can
easily determine, how long will it take to reach that target
value.
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Timer Example We like to light a LED after 10 ms. The timer is
16-bit (16 flip flops
cascaded) and the internal clock frequency is 1 MHz.
The real problem is that how the processor or controller will
know
that 10 milliseconds have passed away.
If we set the target count as 10000, the timer will generate
an
interrupt when its value equals 10000.
The time taken to count up to 10000 =
= 10 ms
If we have configured the timer to generate an interrupt when
it
reaches the target count, it will generate interrupt after exact
10 ms.
At the interrupt, the processor will know that now its time to
light the
LED.
6101
10000ValueCount
=
CLKf
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Timer Module on DSP C6713
DSP TMS320C6713 has two timer modules, each 32-bits,
Timer 0 and Timer 1.
Timer 0 is reserved for the processor itself.
Timer 1 is available to the system designer.
Timer module can be configured to take clock internally or
externally. C6713 operates on clock frequency 225 MHz. Timer
module
can be configured to take one-fourth or one-eighth of this
frequency as input. The target values of timer can be set from 1
to 232-1( 4.3 x
109).
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Example Problem
How will you configure timer 1 of the DSP
C6713 if you want to generate interrupt after100 ms.
fCLK
= ________ (options: 225/4 MHz, 225/8 MHz)
Target count = _________ (options: 1 to 232-1)
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Announcements
Next Monday you may have a quiz.
Final viva has been scheduled next week. Date and time
will be announced shortly. The last two assignments are due on
12th May 2009 (FIR
filter assignment and todays assignment).
Distribution of marks for DSP lab is as under.
Assignments: 10
Quiz: 2.5
Practical Exam: 2.5
Final Viva: 5
