A Play Core Timer Interrupts Acted by the Human Microcontroller Ensemble from ENCM415

6/3/2015 CORE Timer Interrupts -- a play, Copyright M. Smith, ECE, University of Calgary, Canada 2 / 21 Unanswered questions 1.What does “volatile” mean? 2.Why will “optimized code” probably not work if volatile is not used? 3.How do you tell C++ that this function is an ISR and not a standard function? 4.Why do you need to tell C++ that this function is an ISR and not a standard function? 5.What is the difference (in coding) between an ISR and a standard function? 6.How does an interupt get latched, why and where? 7.Why do I have to tell the timer that the interrupt has been serviced, and how do I do it? 8.Remind me to ask Googan to help me with the “human microprocessor example” on Thursday. Task 2 – file 2 (C++ or ASM) extern volatile int foo_flag; Tell “C++” that I am not a function but I am an ISR – interrupt service routine void ISR_count( ) { foo_flag--; Tell the timer that the interrupt has been serviced }

6/3/2015 CORE Timer Interrupts -- a play, Copyright M. Smith, ECE, University of Calgary, Canada 3 / 21 Timers available on Blackfin Watchdog timer – Hardware Reference Core timer – Hardware Reference General purpose timers 15-1 –Pulse Width Modulation –Pulse Width Count and Capture –External Event Application of timers to provide code safety and improved version of UseFixedTimeASM( ) Introduction to timer interrupts

6/3/2015 CORE Timer Interrupts -- a play, Copyright M. Smith, ECE, University of Calgary, Canada 4 / 21 Act 1 – The MAIN task

6/3/2015 CORE Timer Interrupts -- a play, Copyright M. Smith, ECE, University of Calgary, Canada 5 / 21 Main.cpp as assembly code Debug option Number of interrupts checked In loop

6/3/2015 CORE Timer Interrupts -- a play, Copyright M. Smith, ECE, University of Calgary, Canada 6 / 21 Main.cpp as assembly code Release option Number of interrupts NOT checked In loop

6/3/2015 CORE Timer Interrupts -- a play, Copyright M. Smith, ECE, University of Calgary, Canada 7 / 21 Main.cpp as assembly code Release option “Volatile” used

6/3/2015 CORE Timer Interrupts -- a play, Copyright M. Smith, ECE, University of Calgary, Canada 8 / 21 How NOT to add a C++ interrupt service routine Standard return From subroutine

6/3/2015 CORE Timer Interrupts -- a play, Copyright M. Smith, ECE, University of Calgary, Canada 9 / 21 How NOT to add a C++ interrupt service routine Since ISR’s can be caused to happen at “ANY” time by external signals you can’t code parameter passing or parameter returning

6/3/2015 CORE Timer Interrupts -- a play, Copyright M. Smith, ECE, University of Calgary, Canada 10 / 21 A proper C++ ISR Save and recover of all registers (volatile and nonvolatile) After recovering all registers we need to RTI -- return from interrupt NOT return from subroutine FP? ASTAT? Is saving all registers needed R7 and P1 enough?

6/3/2015 CORE Timer Interrupts -- a play, Copyright M. Smith, ECE, University of Calgary, Canada 11 / 21 The Core Timer Registers Core Timer Scale Register TSCALE –Requires ability to communicate with TCOUNT register Core Timer Count Register TCOUNT –Requires ability to count backwards in steps of TSCALE + 1 Core Timer Period Register TPERIOD –Requires ability to communicate with TCOUNT register Core Time Control Register TCNTL –Leadership role – has ability to put timer into low power mode, disable timer, enable auto reload feature which place TPERIOD into TCOUNT whenever TCOUNT reaches zero (causing an interrupts). Has a “sticky bit”

6/3/2015 CORE Timer Interrupts -- a play, Copyright M. Smith, ECE, University of Calgary, Canada 12 / 21 Core Timer Action You set Core timer register TSCALE to 0 (decrement by 0 + 1) You set register TPERIOD to 0x2000 You set register TCOUNT to 0x4000 You enable timer using control register TCNTL TCOUNT is decreased by 1 until it reaches 0 (0x4000 system clock ticks) When TCOUNT reaches 1, interrupt is caused and TCOUNT is reloaded with TPERIOD (0x2000) – counts down again

6/3/2015 CORE Timer Interrupts -- a play, Copyright M. Smith, ECE, University of Calgary, Canada 13 / 21 The play is about to start

6/3/2015 CORE Timer Interrupts -- a play, Copyright M. Smith, ECE, University of Calgary, Canada 14 / 21 Now we need to add the actors Main( ) -- 2 actors Doing something Number_Interrupts ISR routine – 1 actor

6/3/2015 CORE Timer Interrupts -- a play, Copyright M. Smith, ECE, University of Calgary, Canada 15 / 21 The play starts The main program and ISR operation will now be demonstrated

6/3/2015 CORE Timer Interrupts -- a play, Copyright M. Smith, ECE, University of Calgary, Canada 16 / 21 Now we need to add the actors Timer – 4 parts Core Timer Scale Register TSCALE Core Timer Count Register TCOUNT Core Timer Period Register TPERIOD Core Time Control Register TCNTL

6/3/2015 CORE Timer Interrupts -- a play, Copyright M. Smith, ECE, University of Calgary, Canada 17 / 21 Starting the play Attempt 2 Main( ) -- 2 actors Doing something Number_Interrupts ISR routine – 1 actor

6/3/2015 CORE Timer Interrupts -- a play, Copyright M. Smith, ECE, University of Calgary, Canada 18 / 21 Important system registers Core interrupt mask register IMASK –Must be super person with ability to stop / start all interrupts in the world –Controls IVTMR interrupt bit Core Interrupt Latch register ILAT –Has ability to remember if interrupt has occurred (been latched) but is being ignored – bits set to zero when interrupt has been accepted Core Interrupt Pending Register IPEND –Read but not written – indicates that interrupt is active or nested

6/3/2015 CORE Timer Interrupts -- a play, Copyright M. Smith, ECE, University of Calgary, Canada 19 / 21 Now we need to add the actors Timer – 4 parts Core Timer Scale Register TSCALE Core Timer Count Register TCOUNT Core Timer Period Register TPERIOD Core Time Control Register TCNTL CORE SYSTEM REGISTERS – 1 person with many hands Core interrupt mask register IMASK Core Interrupt Latch register ILAT Core Interrupt Pending Register IPEND

6/3/2015 CORE Timer Interrupts -- a play, Copyright M. Smith, ECE, University of Calgary, Canada 20 / 21 Real demonstration Main( ) -- 2 actors Doing something Number_Interrupts ISR routine – 1 actor Timer registers – 4 actors Core registers – 1 actor

6/3/2015 CORE Timer Interrupts -- a play, Copyright M. Smith, ECE, University of Calgary, Canada 21 / 21 Real demonstration Main( ) -- 2 actors Doing something Number_Interrupts ISR routine – 1 actor Timer registers – 4 actors Core registers – 1 actor