ECE 271 Microcomputer Architecture and Applications University of Maine

Transcription

1 ECE Microcomputer Architecture and Applications Lab : Pulse Width Modulation Instructor: Prof. Yifeng Zhu Spring Goals. Understand the concept of Pulse Width Modulation (PWM). Use PWM to control the LED brightness Pre-Lab Assignment. Read Chapter. Complete the pin and timer configuration tables Lab Demo. Periodically dimming a LED. Use an oscilloscope to measure duty cycles.. Something cool. Note that dimming another LED does not count as something cool. The following gives a few example of something cool. a. Use PWM to control stepper motors to perform micro-stepping b. Use PWM to generate a music tone (a -Hz sine wave, tone A) c. Adjust PWM accuracy by calibrating the accuracy of MSI. Post-Lab Assignment. Complete the post lab report and write your answer in Readme.md Timer Control for Channel of Timer X: External Trigger input (ETRF) slave mode control register OCREF clear selection Output Compare Reference (OCREF) Capture/Compare output Polarity: : OC active high : OC active low capture/compare enable register Capture/Compare output enable : Off - OC is not active : On - OC signal is output on the corresponding output pin capture/compare mode register Output compare mode : Frozen : Toggle : Force inactive level : Force active level : PWM mode : Up counting: active if CNT < CCR, else inactive Down counting: active if CNT > CCR, else inactive : PWM mode Up counting: inactive if CNT < CCR, else active Down counting: inactive if CNT > CCR, else active TIMx PWM Mode TIMx_APR (Auto-Reload register): frequency TIMx_CCRx (Capture/Compare register): duty TIMx_CCMRx (Capture/Compare Mode register): OCxM for PWM mode or OCxPE to enable preload TIMx_EGR (Event Generation register): UG to Re-initialize the counter and generates an update of the registers TIMx_CCER (Capture/Compare Enable register): CCxP for polarity and CCxE for enabling TIMx_CR (Control register ): ARPE: Auto-reload enable: CMS for edge-align mode or center-aligned mode TIMX_DIER (DMA/Interrupt Enable register)

2 USER All PINs for touch sensors are not extended. USER Pushbutton: PA GREEN LED: PB BLUE LED: PB Touch sensor: PA, PA (group ), PC, PC (group ), PB, PB (group ) If JP is on, PC is used for DD_CNT_EN DAC_CH DAC_CH Touch sensor ST- Link Touch sensor Touch sensor Boot BLUE LED GREEN LED Reset Free I/O Pins: PA, PA, PA, PC, PD Figure. PIN Connection of STML-Discovery Board The above diagram shows the functions of each pin. The blue and green LED is connected to the PB pin and the PB pin, respectively. The following table shows the alternative functions available for these two pins. This shows: LED Pin Available Alternative Functions Blue PB IC_SCL/TIM_CH/USART_TX Green PB IC_SDA/TIM_CH/USART_RX/PVD_IN PB pin can be programmed to connect to Channel of Timer, and PB pin can be connected to Channel of Timer.

3 Comments about comments Properly documenting is especially important for assembly programs. Thumb of Rule: If you are able to easily and quickly modify your codes one year after your initial development, then your code comments are excellent. When writing comments, you can assume that readers of your codes know the assembly syntax but do not know your program goals, logic, and methodology. Give meaningful name to registers Recommend to using corresponding C code to make comment Instruction Bad comment Good comment add r, r, # ; add one to a register ; array_index++ sub r, r, # ; r = r - ; counter++ mul r, r, r ; r = r * r ; distance = speed * time Specific Requirements For each subroutine (also called function or procedure), your program should have a comment header. Your program should include a register usage page. Give each register a meaningful name. Here is an example. ; Name: strcat ; Description: Concatenate two strings ; Input: r pointer to the first string ; r pointer to the second string ; Returns: r pointer to the resulting string ; usage: ; r array index i of the second string ; r array index j of the resulting string ; r temporary value to hold a char loaded from memory strcat PROC... ENDP

4 Lab : Pre-Lab Assignment NOTE: The Blue LED (PB ) is connected to the Channel of Timer. The Green LED (PB ) is connected the Channel of Timer.. Configure RCC_AHBENR to enable the clock of GPIO Port B Student Name: AHBENR Mask FSMCEN AESEN DMAEN DMAEN FLITFEN CRCEN GPIOPGEN GPIOPFEN GPIOPHEN GPIOPEEN GPIOPDEN GPIOPCEN GPIOPBEN GPIOPAEN Write your assembly code below to enable the GPIO B clock:. Configure RCC_APBENR to enable the clock of Timer APBENR Mask COMPEN DACEN PWREN USBEN ICEN ICEN USARTEN USARTEN USARTEN USARTEN SPIEN SPIEN WWDGEN EN TIMEN TIMEN TIMEN TIMEN TIMEN TIMEN Write your assembly code below to enable the Timer clock:

5 . Configure PB (Blue LED), PB (Green LED) as Alternative Function Mode GPIO Mode: Input (, reset), Output (), AlterFunc (), Analog () GPIOB MODER MODER MODER MODER MODER MODER MODER MODER MODER MODER MODER MODER MODER MODER MODER MODER MODER Mask GPIOB Mode MASK = x (in HEX) GPIOB Mode = x (in HEX). Configure and Select the Alternative Function for PB (Blue LED), PB (Green LED) GPIOx_AFRL[:] defines the alternate function for pins to, and GPIO_AFHL for pins to. GPIOB AFR[] AFRL[:] AFRL[:] AFRL[:] AFRL[:] AFRL[:] AFRL[:] AFRL[:] AFRL[:] MASK VALUE GPIOB AFR[] AFRH[:] AFRH[:] AFRH[:] AFRH[:] AFRH[:] AFRH[:] AFRH[:] AFRH[:] MASK VALUE GPIOB Alternative Function [] MASK = x (in HEX) GPIOB Alternative Function [] = x (in HEX) GPIOB Alternative Function [] MASK = x (in HEX) GPIOB Alternative Function [] = x (in HEX)

6 . Complete the following table to configure the PWM output for Channel of Timer TIMx_CR CKD ARPE CMS DIR OPM URS UDIS CEN TIMx_CR TIS MMS[:] CCDS Reserve d TIMx_CCMR Output Compare mode OCCE OCM [:] OCPE OCFE CCS OCCE OCM [:] OCPE OCFE CCS TIMx_CCMR Output Compare mode OCE OCM [:] OCPE OCFE CCS OCCE OCM [:] OCPE OCFE CCS TIMx_CCER value CCNP CCP CCE CCNP CCP CCE CCNP CCP CCE CCNP CCP CCE TIMx_CCR CCR[:] (TIM only, reserved on the other timers) CCR[:] value TIMx_PSC value PSC[:] TIMx_ARR ARR[:] (TIM only, reserved on the other timers) ARR[:] value

7 ECE Microcomputer Architecture and Applications Lab : Pulse Width Modulation Lab Demo Demo : Diming an LED Demo : Use an oscilloscope to measure duty cycles. Keep TIM_ARR fixed but set TIM_CCR to three different values. TIM_ARR = TIM_PSC = Student Name: Case TIM_CCR Pulse Width Measured # TIM_CCR = /* TIM_ARR Pulse Period Measured Duty Cycle Measured # TIM_CCR = /* TIM_ARR # TIM_CCR = /* TIM_ARR ECE Microcomputer Architecture and Applications Lab : Pulse Width Modulation Post-Lab Assignment. Suppose the HSE (high-speed external clock) of MHz is selected the clock of a timer. In order to generate Hz square wave with duty cycle of %, how would set up the timer? Indicate your counting mode and show the value of ARR, CRR, and PSC registers.. Do you have any suggestions or comments for this lab, the textbook or the lab?