ME 4447/6405 Interrupts and Resets Suzanne Price Scott Gilliliand Greg Graf

Overview Polling Interrupts Vector Tables Highest Priority Interrupt Register ADC Example with Interrupts Resets Standby Modes Suzanne Price

Waiting for an Event : Polling Program can “poll” for a value to change We saw this in our ADC lab: Prevents processor from running other code We could not easily control LED’s while checking the ATDC. WATCHLDAAATDSTAT1;Load the ADC register ANDA#$80;Get only the conversion complete flag BNEWATCH;Loop if conversion is not complete Suzanne Price

Waiting for an Event: Interrupts User defined section of code that runs automatically when an event occurs Completion Flag Change in Pin Voltage Errors Others Suspends main program execution while interrupt is serviced Can happen at any time (when enabled) Maskable and Non-Maskable Interrupts Suzanne Price

How Interrupts Work: Review Event occurs Current instruction finishes If interrupts are enabled: Push registers to stack Set interrupt bit(s) in CCR Run Interrupt Service Routine (ISR) until RTI Pull register values back from stack Main program continues to run Suzanne Price

Non-Maskable Interrupts 6 Non-Maskable Interrupts Higher Priority than maskable interrupts Can interrupt Maskable Interrupt ISRs X=1 ONLY disables XIRQ interrupt (and all other interrupts are still enabled when X=1) 1.POR of RESET pin 2.Clock monitor reset 3.COP watchdog reset 4.Unimplemented instruction trap 5.Software interrupt (SWI) 6.XIRQ interrupt Suzanne Price

Non-Maskable Interrupts At Reset or during Non-Maskable interrupt X=1 and I=1 Interrupts cannot be serviced Clear X bit TAP instruction ANDCC #$40 instruction Software cannot set X bit once cleared unless non-maskable interrupt occurs RTI restores X and I bits to pre-interrupt state Suzanne Price

Non-Maskable Interrupts XIRQ Externally triggered PE0 pin low = XIRQ interrupt SWI Allows an interrupt without an event MON12 in use: jumps back to DBug12 Unimplemented Instruction Trap CPU is given code with invalid opcode Generates interrupt request to unimplemented instruction trap vector Suzanne Price

Maskable Interrupts 27 Maskable Interrupts Global Masking: controls execution of all maskable interrupts (ie. I bit =1, no maskable interrupts occur) Local Masking: controls execution of interrupt on a peripheral device (ie. ATD) 1.IRQ 2.Real-Time Interrupt 3.Standard Timer Channel 0 4.Standard Timer Channel 1 5.Standard Timer Channel 2 6.Standard Timer Channel 3 7.Standard Timer Channel 4 8.Standard Timer Channel 5 9.Standard Timer Channel 6 10.Standard Timer Channel 7 11.Standard Timer Overflow 12.Pulse Accumulator A Overflow 13.Pulse Accumulator Input Edge 14.SPI transfer Complete 15.SCI system 16.ATD 17.Port J 18.CRG PLL Lock 19.CRG Self Clock Mode 20.Flash 21.CAN Wakeup 22.CAN Errors 23.CAN Receive 24.CAN Transmit 25.Port P 26.PWM Emergency Shutdown 27.VREG LVI Suzanne Price

Maskable Interrupts IRQ Only external maskable interrupt signal IRQE bit on IRQCR Register IRQE=1: Falling Edge Sensitive IRQE=0: Low Level-Sensitive Peripheral Subsystems (all other Maskable Interrupts) Flag bit and interrupt enable bit ATD, Timers, PWM, serial communications, etc. Suzanne Price

Highest Priority Interrupt (HPRIO) Register HPRIO register moves one maskable interrupt to top of priority list Cannot change priority of non-maskable interrupts Procedure to increase priority of maskable interrupt: Set I bit to disable maskable interrupts Write low byte of interrupt vector to HPRIO Clear I bit to re-enable maskable interrupts Address: $001F Suzanne Price

Highest Priority Interrupt Register (HPRIO) Address: $001F Bit 7Bit 6Bit 5Bit 4Bit 3Bit 2Bit 1Bit PSEL7PSEL6PSEL5PSEL4PSEL3PSEL2PSEL1- PSEL[7:1] – Priority Select Bits Selects one interrupts source to be elevated Can only be written while I-bit in the CCR is set and maskable interrupts turned off Write the low byte of the maskable interrupt vector to HPRIO to elevate that maskable interrupt to the highest priority Ex: writing $DE to HPRIO elevates the Standard Timer Overflow to highest priority (Standard Timer Overflow vector = $FFDE) Suzanne Price

Interrupt Vector: stores starting address of ISR Interrupt Vector Table List of all interrupt vectors used by processor Stored at $FF00 - $FFFF Interrupt Vector Table

MON12 and Interrupt Vector Tables MON12 stores its own interrupt vectors in $FF00-$FFFF In order to have an interrupt vector called, it must be placed in second table, stored in $0F00-$0FFF because user cannot write to EEPROM This table is found in the CML-12C32 reference manual that came with the board The MON12 Interrupt Table showing both the actual Vector Table addresses, and the Ram Vector Table addresses Scott Gilliland

MON12 and Interrupt Vector Tables On an interrupt under MON12: The microcontroller calls the ISR in the $FFxx range MON12’s calls the ISR specified by the user in the $0Fxx range The user’s ISR is run from the address specified in $0Fxx To the user, it appears that the Interrupt Vector Table has moved to $0F00-$0FFF Scott Gilliland

ADC Interrupt Example : ISR Write an Interrupt Service Routine to be run whenever an ADC interrupt occurs ISR stores latest value in memory for later use Ensure that Sequence Complete Flag is cleared Needed to allow the next interrupt to happen Write $80 to ATDSTAT0 to clear flag Scott Gilliland

ADC Interrupt Example : ISR *Interrupt Service Routine ORG$2000 LDAA ATDSTAT0 LDAAATDDR0H STAALSTCONV LDAA#$80 STAA ATDSTAT0 RTI Define a starting address Read Status register Read Result register Store Value to a reserved memory location Reset SFC flag by writing a ‘1’ to it Ensures that we will get the next interrupt Finally, call RTI to return from the ISR and pull register values back from the stack Scott Gilliland

ADC Interrupt Example: Setup Set up Interrupt Vector Table for the ADC Interrupt Needs to be the address of the first instruction of the ISR Set up ADC Including ASCIE bit to enable ADC interrupts Enable global maskable interrupts Processor is now free to run other code Print the value stored into memory by the ISR Scott Gilliland

ADC Interrupt Example: Setup ORG $1000 SEI LDX #$2000 STX $0FD2 LDAA #% STAAATDCTL2 LDAA #% STAAATDCTL4 LDY#41 DELAY1DEY BNEDELAY1 CLI Setup the ADC, including setting the ASCIE bit to enable local ADC interrupts Set I bit to make Interrupt Vector Table changes safe Store the address of our ISR ($2000) to the Interrupt Vector for the ADC ($0FD2) Wait for the ADC to fully power up, and then clear the I-bit to enable all maskable interrupts Scott Gilliland

ADC Interrupt Example: Full Code ATDCTL2 EQU$0082 ATDCTL4EQU$0084 ATDCTL5EQU$0085 ATDDR0HEQU$0090 LSTCONVEQU $800 OUTSTRGEQU$FF5E ATDSTAT0EQU$0086 ORG$802 STRING1FCC"The voltage is " V1RMB1 FCC". " V2RMB1 FCC" Volts" FCB$0A,$0D,$04 ORG $1000 SEI LDX #$2000*Start of ISR STX $0FD2*ATD Service Routine Vector LDAA #% *ADPU = 1, ASCIE=1, ASCIF=0 STAAATDCTL2 LDAA #% *SRES8=1, Prescaler bits = STAAATDCTL4 LDY#41*STD Converter Startup Delay DELAY1DEY BNEDELAY1 CLI Loop ******* *Many other calculations may be performed here ****** LDAA#$00*Load D with LSTCONV LDABLSTCONV LDX#51*Load x with #51 IDIV *Divides D by X ->D:X XGDX ADDB#$30 STABV1*Stores B to v1 XGDX LDAA#10*Load A with 10 MUL*Multiply A and B (low byte of D) LDX#51 IDIV XGDX ADDB#$30 STABV2*Stores B to v2 LDX #STRING1 JSR OUTSTRG LDAA#% *Scan=0, MULT=1, cc:CA=000 STAA ATDCTL5 *Start Conversion JMP Loop *Interrupt Service Routine ORG$2000 LDAA ATDSTAT0 LDAAATDDR0H STAALSTCONV LDAA#$80*Scan=0, MULT=1, cc:CA=000 STAA ATDSTAT0 *Start Conversion RTI END Define Constants (ex: ATDCTL4) Define Strings and reserve memory Setup ADC and ADC Interrupt Run any other code Convert value and print to serial Interrupt Service Routine Scott Gilliland

Resets Forces MCU to: Assume set of initial conditions Begin executing instructions at an assigned starting address Like interrupts, resets have a vector to define the starting address of code to be run Unlike interrupts, they do not return to original code location Resets have different vectors to allow execution of individualized code Greg Graf

Resets: Process Flow When a reset is triggered: The address from the vector is loaded into the program counter S, X, and I bits are set in the CCR MCU hardware is initialized to reset state Check for any interrupts that have occurred Greg Graf

Resets: POR, External, Low Power Power on Reset (POR) Triggered when Vdd is applied Timing circuit is initialized, and allowed to settle for 4064 cycles External Reset (RESET) Same vector as POR Reset pin must be pulled low for a total of 6 cycles Low Power Reset Same vector as POR Triggered when Vdd drops below acceptable limit Greg Graf

Resets: COP, Clock Monitor Computer operating Properly (COP) Reset Protects against software failures (infinite loops, etc) When enabled (NOCOP bit in CONFIG register), resets if free-running watchdog timer rolls over $FFFF Timer rate is set in the OPTION register. System E- clock is divided by 2 15 and further scaled by 1, 2, or 4 Clock Monitor Reset Protects against clock failure Set by CME control bit If enabled, system resets if no clock edges are detected within a set period. Greg Graf

Standby Modes Suspends CPU operation until reset or interrupt occurs Reduces power consumption CPU registers are stacked to speed up recovery into interrupts Two modes: Wait, Stop Greg Graf

Standby Modes: WAIT (WAI) Suspends CPU Processing On-chip crystal oscillator remains active Peripherals keep running Wait mode is exited through IRQ, XIRQ, or any internally generated interrupts Greg Graf

Standby Modes: Stop (STOP) All clocks and peripherals stopped I/O pin levels remain static Stop is exited through external interrupts, edge-triggered IRQ or RESET pin XIRQ always exits stop mode, but XIRQ interrupts are only executed if X bit is clear Otherwise, code continues from STOP command If S-bit in CCR is set, STOP is treated as NOP Greg Graf

References ME 4447/6405 Interrupts and Resets Lecture HCS12 Reference Manuals

Appendix: Full Code ATDCTL2 EQU$0082 ATDCTL4EQU$0084 ATDCTL5EQU$0085 ATDDR0HEQU$0090 LSTCONVEQU $800 OUTSTRGEQU$FF5E ATDSTAT0EQU$0086 ORG$802 STRING1FCC"The voltage is " V1RMB1 FCC". " V2RMB1 FCC" Volts" FCB$0A,$0D,$04 ORG $1000 SEI LDX #$2000*Start of ISR STX $0FD2*ATD Service Routine Vector LDAA #% *ADPU = 1, ASCIE=1, ASCIF=0 STAAATDCTL2 LDAA #% *SRES8=1, Prescaler bits = STAAATDCTL4 LDY#41*STD Converter Startup Delay DELAY1DEY BNEDELAY1 CLI Loop ******* *Many other calculations may be performed here ****** LDAA#$00*Load D with LSTCONV LDABLSTCONV LDX#51*Load x with #51 IDIV *Divides D by X. Stores remainder to D and the result in X XGDX ADDB#$30 STABV1*Stores B to v1 XGDX LDAA#10*Load A with 10 MUL*Multiply A and B (low byte of Remainder in D) LDX#51 IDIV XGDX ADDB#$30 STABV2*Stores B to v2 LDX #STRING1 JSR OUTSTRG LDAA#% *Scan=0, MULT=1, cc:CA=000 STAA ATDCTL5 *Start Conversion JMP Loop *Interrupt Service Routine ORG$2000 LDAA ATDSTAT0 LDAAATDDR0H STAALSTCONV LDAA#$80*Scan=0, MULT=1, cc:CA=000 STAA ATDSTAT0 *Start Conversion RTI End

Interrupt Flow Interrupt condition is met Restore Registers w/ org. Values Standard Interrupt Table Analyze Priority Store all registers on the Stack Global Masking Local Masking Continue Program Complete Current Instruction A Set (I) or (X) to prohibit another Interrupt Load Address in appropriate vector YES NO YES ISR instruction Clear I or X bit in CCR RTI YES NO B B A Note: Local mask must be cleared prior to performing RTI