1

Issues surrounding Lab. 3 and Lab. 4

Lab. 3 – Accurate timing to measure temperature

Lab. 4 – Accurate timing signals to send temperature value to LCD screen

2

How accurate does the temperature sensor timings need to be?

T = 255 – 400 * T1 / T2

If T = 25 then T1 / T2 = 230 / 400Where T1 + T2 is around 1 / 30 s so T1 around 1/90 s

Can use these ideas to validate CalculateTemp( ) task Part of the testing procedure for Lab. 3 – T is a float 25.4 etc whereas T1 and T2 are “counts” – see last lecture

3

How accuracte do we need to measure T1 and T2

T = 255 – 400 * T1 / T2 – Differentiate to get error estimates

Worse case -- all errors add updT = 400 * dT1 / T2 + 400 * T1 * dT2 / T2 ^ 2

Percentage error calculations dt / T, dT1 / T1, dT2 / T2dT / T = 400 * dT1 / T2 / T + 400 * T1 * dT2 / T2 ^ 2 / T

For T = 25 C and T1 and T2 around 1 / 60 s – If 1% error in T1 and T2 what is accuracy in T

4

Back of envelope calculationCLICKER RESPONSE 1

Percentage error calculations dT1 / T1, dT2 / T2 = 1%dT / T = 400 * dT1 / T2 / T + 400 * T1 * dT2 / T2 ^ 2 / T

dT / T = dT1 / T1 * 400 * T1 * / T2 / T + dT2 / T2 * 400 * T1 / T2 / T

= 1% * 400 * (1/90) / (1/45) / 25 + 1% * 400 * (1/90) / (1/45) / 25

What is accuracy in dT / T for 1% accuracy in T1 and T2A) Better than 1% B) around 2% C) around 4% D) worse than 6%

5

We need to find the rising edge of TMP03 signal shape – better than 1%

• Rising edge is “looked for” every PERIOD where period is fraction of milliseconds– TTCOS(MeasureTemp, NO_DELAY, Milli-Seconds)

• If another task gets executed then accuracy of Measure Temp( ) is lost– TTCOS(FlashLED, NO_DELAY, 1/20 S)– TTCOS(MeasureTemp2, NO_DELAY, Milli-Seconds)– TTCOS(MeasureTemp3, NO_DELAY, Milli-Seconds)

6

Solve this problem by“time multiplexing tasks – pre-schedule”

TTCOS(LED6, NODELAY, EVERY_SECOND / 2)TTCOS(LED5, NODELAY + 1ms, EVERY_SECOND / 2)TTCOS(AllTasks, NODELAY + 2 ms, EVERY_SECOND)TTCOS(Lab4_SPI_LCD

where AllTasks( ) isTTCOS(Temp1, NODELAY, RUN_ONCE) // Measure 4 or 5 TimesTTCOS(Destroy_Temp1, 180MS_DELAY, RUNONCE)TTCOS(Temp2, 360MS_DELAY, RUN_ONCE) TTCOS(Destroy_Temp2, 450MS_DELAY, RUNONCE)

SEE “SMITH” ARTICLE IN CLASS NOTES (ARTICLE 1) – POSSIBLE MIDTERM QUESTION

0 ms 1 ms 2 ms 182 ms 362 ms 452 ms 500 ms 501 ms 502 ms

LED6 LED 5 Temp1 Destroy Temp1

Temp2 DestroyTemp2

LED6 LED5 SPI_LCD(Lab. 4)

7

NOW MOVING PAST MIDTERM QUESTIONS(Up to and including Lab. 2)

And into Post Lab Quiz 3 and Final exam material

REMINDER: ENCM511 MIDTERMTHURSDAY 5th NOVEMBER 6:30 till 8 PMENA 103

8

Loss of battery power

• Basically the TemperatureMeasuring tasks are running every 0.1 ms– Use a lot of battery power– Basically waiting for something to happen

• Measure more accurately using “Hardware” – Blackfin has 3 GENERAL PURPOSE TIMERS to solve

this problem – (automotive industry and other embedded applications

9

TTCOS using GP TimerTTCOS(AllTasks, NODELAY + 2 ms, EVERY_SECOND)

Where AllTasks( ) launches the 2 tasks TTCOS(ActivateTimer, NO_DELAY, RUN_ONCE) TTCOS(CheckTimer, DELAY_100ms, RUN_ONCE)

Where CheckTimer( ) is the task If GP Timer DONE-FLAG is set, read T1 and T2 values

(to an accuracy of 1 / 1,000,000 s accuracy)else TTCOS(CheckTimer, DELAY_100ms, RUN_ONCE)

Check again in a short while that timer has completed

See article 3 in the class notes

10

Where are the inputs to the GP Timersfor use in Lab. 3?

• Input to 2 of the general purpose timers are on the logic lab break-out panel between the PF pins

• Question – First year these are used – how can we test if they work?

PF1

PF5

PF6

PF7

PF8

PF9

PF10

PF11

RST

GP 2 GP 1

11

Reference material for TimersChapter 15 Blackfin Hardware manual

– see class notes

12

13

Timer behaves like McVASH in principle, but not in detail

14

Q2 Watch out how access registers fromC and assembly code

15

Watch out how access registers fromC and assembly

Next question is clicker

16

Q2 -- Which instruction will cause Blackfin to crash

A) *pTIMER_ENABLE = 0x3456;

P0.L = lo(TIMER_ENABLE);P0.H = hi(TIMER_ENABLE); R0 = 0x3456;

thenB) [P0] = R0;C) W[P0] = R0;D) B[P0] = R0;

17

Task_ActivateTimerStart AFTER setting other registers

• Used to start timer -- use OR operation

• Stop timer – W1C – DO NOT USE OR, DON’T USE AND

18

Task_Has_Timer_Captured_SignalRun once – ignore, use second result

• Timer changes these bits from 0 to 1• You must write 1 into these bits to change to 0

POLL FOR THISBIT TO CHANGE

19

TIMER0_CONFIG, TIMER1_CONFIG

DISABLEINTERRUPTSAS WEARE POLLINGTHE TIMERS

20

Read the PERIOD and WIDTH – ONLY after device has indicated it is ready

21

How are we going to test?• Hook up PF7 (output) to PF8 (input)• Hook up PF7 (output) to “Timer 0” (input)

• InitGPIOFlags( ); (Lab. 1)• ChangePF7_to_Output( );• Switches = Read GPIOFlags( ); Lab. 1• CHECK(PF8 (SW1) == 0);• WriteGPIOFlags(PF7) – turns PF8 on• Switches = Read GPIOFlags( ); Lab. 1• CHECK(PF8 (SW1) == 0);• THIS CHECKS THAT PF7 works as an output

PF1

PF5

PF6

PF7

PF8

PF9

PF10

PF11

RST

GP 2?GP 1?

GP 1?GP 0?

22

Write a Routine that activates all timers in Pulse capture mode

• InitGPIOFlags( )• TurnPF7 to output ( )• Turn on all timers( ) • For count = 1 to 8

– WaitAWhile(4000);– WritePFFlags(PF7); -- pulse on– WaitAWhile(8000);– WritePFFlags(0); , pulse off

• Turn off All timers ( )• Check the Timer status register to see which timer is being

pulsed – its IRQ request should be set

23

Q3 -- If timer 2 is active and captured signalWhat value when read STATUS?

A) 0x02 B) 0x04 C) 0x22 D) 0x44

24

Q4 -- If both timer 1 and timer 2 are active, what operation clears "timer 1 done flag" (bit 1 TIMIL1 -- W1C)?

A) Read STATUS, AND with ~0x2, Write STATUSB) Write STATUS with 0x2C) Read STATUS, OR with 0x1, Write STATUS D) Read STATUS, OR with 0x2, Write STATUS

25

For Lab. 3 need to slightly modify“time multiplexing tasks – pre-schedule”

TTCOS(LED6, NODELAY, EVERY_SECOND / 2)TTCOS(LED5, NODELAY + 1ms, EVERY_SECOND / 2)TTCOS(AllTasks, NODELAY + 2 ms, EVERY_SECOND)TTCOS(Lab4_SPI_LCD

where AllTasks( ) isTTCOS(Temp1, NODELAY, RUN_ONCE) // Measure 4 or 5 TimesTTCOS(Destroy_Temp1, 180MS_DELAY, RUNONCE)

SEE “SMITH” ARTICLE IN CLASS NOTES (ARTICLE 1 AND ARTICLE 3)

0 ms 1 ms 2 ms 182 ms 362 ms 452 ms 500 ms 501 ms 502 ms

LED6 LED 5 Temp1 Destroy Temp1

LED6 LED5 SPI_LCD(Lab. 4)