Lecture 22 - Time Keeping II

- Recap
- Do demonstration
- Explain connectivity
- Explain board
- Input capture
- Interrupt

10:10 Recap

We are discussing Timer_A modules, with input capture and output compare.

- 16-bit Timer_A module
    Programmable divider
	Programmable counting mode (up/updown/continuous)
	
  TA0 .. TA3
  
- Input Capture/Output Compare channels
    TAxCCRy capture-compare register

	TAxCCR0 is special purpose; serves as period register
	in up/updown counting modes, as well as for output compare.
	
	TAxCCR1,2,3,4 are additional capture-compare registers

- Connectivity

		The timer IC/OC channels are marked as TAx.y

	Check the data sheet pin for port 2.6 -> TA0.3

	This means that GPIO 2.6 is multiplexed with TA0/3 (IC/OC)
	
	So this pin can serve:
		- as GPIO input
		- as GPIO output
		- as IC channel for TA0CCR3
		- as OC channel for TA0CCR3
		
	Question:
	
		What is the TA IC/OC channel for the Green LED
		
		Green LED on Boost XL is P2.4
		Pin P2.4 is attached to TA0.1
		
		So green LED is driven by IC/OC channel TA0CCR1

    J4.39       Red Led     TA0.3       P2.6
    J4.38       Green Led   TA0.1       P2.4
    J4.37       Blue Led    TA2.1       P5.6
    J4.36       not used    TA2.3       P6.6
    J4.35       not used    TA2.4       P6.7
    J4.40       Buzzer      TA0.4       P2.7
	
	Documentation needed:
		- Datasheet lists the pinout
		- BoostXL user guide and launchpad user guide explain connectivity

10:20 Output Compare events

				   When timer 		When timer 
				   reaches			reaches
				   TAxCCRn			TAxCCR0

	Set				Set				/
	Toggle/Reset	Toggle			Reset
	Set/Reset		Set				Reset
	Toggle			Toggle			/
	Reset			Reset			/
	Toggle/Set		Toggle			Set
	Reset/Set		Reset			Set
		
In continuous mode, the timer runs from 0 to FFFF.
  - When it hits TAxCCRn, it does the first activity
  - When it hits TAxCCR0, it does the second activity
  
- Example from previous lecture:

   msp432-compare-0
	
   TA0CCR0 is set at 0x8000
   TA0CCR3 is set at 0x1000
   Mode is SET/RESET

   So, timer runs from 0 to FFFF
   When it hits 0x1000, it is set
   When it hits 0x8000, it is reset

         +----------+
         |          |
   +-----+          +----------------+
  0x0   0x1000     0x8000         0xFFFF
 
- Why is it useful to have multiple TAxCCRy? 
  Because you can generate precisely related signals
  
  Example 2: msp432-compare-1
  
   TA0CCR0 is set at 0x3FFF
   TA0CCR3 is set at 0x0000
   TA0CCR1 is set at 0x2000
   Mode is SET/RESET
   
   What waveform will we see?
   
   +---------+     
   |         |          
   +         +-----------------------+
  0x0      0x3FFF                 0xFFFF

       +-----+     
       |     |          
   +---+     +-----------------------+
   0x0 0x2000  0x3FFF             0xFFFF
   
- We can also generate symmetrically related waveforms
  using the counter in updown mode

  Example 3: msp432-compare-2
  
    TA0CCR0 is set at 0x8000
	TA0CCR3 is set at 0x6000
    TA0CCR1 is set at 0x2000
    Mode is TOGGLE/SET
	
   What waveform will we see?
   
             +------:------+
             |      :      |
   +---------+      :      +---------------+
   0x0    0x6000 0x8000

        +-----------:-----------+
        |           :           |
   +----+           :           +----------+
   0x0 0x2000    0x8000
   
10:30 Input Capture

In the case of Input Capture, we copy the value of TAx into TAxCCRy

The input capture event can be tied to the rising edge, falling edge,
or both.

The classic application of input capture is frequency measurement:

        Capture                   Capture
        +---------------+         +--------------+
        |               |         |              |
  +-----+               +---------+              +------
  
        |||||||||||||||||||||||||||  => count number of cycles 
		                                between two edges
        |                         |
		|                         |
		Value1                    Value2
		
		Delta = Value2 - Value1

		If you know the clock period, you also know the physical
		time needed for Delta.
		
Of course, you can only measure the frequency of signals that are
much slower than the clock.

Other applications of Input Capture are phase measurement and
relative position of the upedge of one signal with respect to the next.

                        +------------------
                        |
	Signal 1  ----------+       +---------
	                            |
	Signal 2  ------------------+
	
	                    |||||||||
	
There are two possible input capture channels per TAxCCRy: CCIA and CCIB
You have to consult the data sheet to ensure that you are looking
at the correct connection.

The input capture example that we will discuss is attached to the
blue LED.

(schematic)

It measures the number of clock cycles that elapse between turn-on events
of the BLUE led.

We are using IC channel TA2.4

To configure the input capture, we have to:
- Configure timerA 2 to run in continuous mode
- Configure input capture TA2.4 to capture upedge
- Write an ISR tied to TA2.4 to read the input-capture value
- Configure the input pins for TA2.4 in IC mode
- Configure the TimerA in continous mode
- Configure the input capture channel in TA2.4

Example (msp432-inputcapture-0)

10:50 Motor Control

(Slides Texas Instruments Motor Compendium)

PWM control of brushless DC motor