Lab6-Prelab

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Embedded Systems International Lab 6 Prelab Name : Lab Partner Name (if you worked together and are submitting the same document or mostly the same answers): Lab Section : Submit your prelab document as a PDF file in Canvas under the corresponding prelab assignment. Every student submits their own prelab. Lab partners are allowed to work on the prelab together and submit the same document (if there is actual collaboration on the document). For full credit, the prelab must be submitted prior to the start of lab. Text responses should be typed or printed neatly. You can draw a sketch by hand, or you can use a drawing tool. Try to have started a rough draft of the prelab when you come to class on Tuesday. Questions 1-7 were included in the Lab 5 Prelab. You selected 4 questions to be graded. The other 3 questions will be graded for this prelab. Circle the questions selected for Prelab 5 and Prelab 6. If none are circled, questions 5-7 will be graded. The same questions cannot be circled for both prelabs 5 and 6. Help your TA by circling the questions properly. 4 questions selected and graded for Prelab 5 : 1 2 3 4 5 6 7 3 questions selected and graded for Prelab 6 : 1 2 3 4 5 6 7 In addition, answer the remaining questions, 8 - 10, in this prelab. 1. Port pins for UART1 transmit (TX) and receive (RX) UART1 is an alternate function, or peripheral, that uses GPIO Port B pins. a) Which Port B pin is used for the UART1 transmit (TX) signal? CPRE 288, ELECTRICAL AND COMPUTER ENGINEERING DEPARTMENT , IOWA STATE UNIVERSITY 1

PB1 b) Which Port B pin is used for the UART1 receive (RX) signal? PB0 2. Use the GPIO port worksheet below to indicate which Port B pin is used for UART1 TX and which Port B pin is used for UART1 RX: write TX and RX in the DATA row of the worksheet under the corresponding pin numbers. What values must be initialized in the other GPIO port registers to configure the UART1 alternate function for the port. Put an “x” in cells that you are not using and should preserve their values. GPIO Port Registers Bit >>> vvv Register 7 6 5 4 3 2 1 0 Description DATA (or PORT pins for alternate functions) X X X X X X U1TX U1RX 0, 1: bit values (or alternate functions) DEN 0 0 0 0 0 0 1 0 1: enable digital AFSEL 0 0 0 0 0 0 1 1 1: enable alternate function PCTL field field field field field field field field Each column in this row is a 4-bit field in the 32-bit PCTL register Refer as needed to the examples on pages 19-28 of the mtg10-notes-concepts-GPIOaltfunc-UART.pdf file and Bai book Table 8.1 (in the notes and slides) (see also Tiva datasheet section 23.4 GPIO Pins and Alternate Functions, Table 23-5, for PMCx Bit Field Encoding). 2

3. Refer to the GPIOAFSEL register description in the Tiva datasheet (Register 10). Refer to the macro definition for the GPIO Port B AFSEL register in the header file, tm4c123gh6pm.h. a. Write the full #define macro definition for the PORTB_AFSEL register as given in the header file. #define GPIO_PORTB_AFSEL_R (*((volatile unsigned long *)0x40005420)) GPIO_PORTB_AFSEL_R |= (0x3); b. What is the 32-bit memory address of this AFSEL register (in hex)? 0x40005420 c. Explain how to determine the register address, i.e., your answer to part b (the memory address for the Port B AFSEL register), from the Tiva datasheet register description (pages 671-672). Hint: Pay attention to the following information from the datasheet pages. Recall that we are using the APB bus on the microcontroller. On the datasheet, it has the base hex value for GPIOAFSEL: 0x4005.9000, and also it says it is offset by 0x420. So, by adding the offset, we get 0x40005420 3

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4. For a baud rate of 115,200, what values should be loaded into the IBRD and FBRD registers? UART Integer Baud Rate Divisor (UARTIBRD), e.g., UART1_IBRD_R UART Fractional Baud Rate Divisor (UARTFBRD), e.g., UART1_FBRD_R Note: A 16 MHz system clock for the TM4C123 microcontroller is used in lab. Also ClkDiv = 16. Refer to any of the following resources about setting the baud rate for a UART on the TM4C123:  In the Bai book, see sections 8.5.3.7 and 8.5.5.2 (also in mtg10-slides-UART.pdf, page 29).  In VY ES book, see section 11.2.2 and information about IBRD and FBRD (remember, we are using the 16 MHz system clock).  In the Tiva datasheet, see section 14.3.2. 5. Consider the UART Line Control register (UARTLCRH). a. Look up this register in the Tiva datasheet (p. 916, try to find it without using the page number). Read the descriptions for the bits. Identify which bits correspond to the following serial communication parameters: 8 data bits, 1 stop bit, no parity, FIFOs disabled, no interrupts For these parameter values, fill in the register bit values in this blank register (assume default/reset values if not specified): Bit 7 6 5 4 3 2 1 0 Value Write a line of code to initialize the UART Line Control register : UART1_LCRH_R = b. What is the 32-bit memory address of UART1 LCRH register (in hex)? 6. Consider the flowchart from Figure 11.8 in section 11.2.3 in Chapter 11 of Valvano and Yerraballi ES online book, http://users.ece.utexas.edu/~valvano/Volume1/E-Book/C11_SerialInterface.htm . This shows a busy-wait or polling approach to receiving data by a UART. 4

The RXFE flag is a bit in one of the UART registers. What is the name of the register? What is the bit number for the RXFE flag? 7. System information - sketch Refer to Video 12.2a (UART Background and Launchpad Support) in Chapter 11 of Valvano and Yerraballi ES online book, http://users.ece.utexas.edu/~valvano/Volume1/E-Book/C11_SerialInterface.htm (section 11.2 UART). Video 12.2a: https://www.youtube.com/watch?v=wdOqQCNWC3c&feature=youtu.be The authors sketch three scenarios for using a UART on the TM4C123 LaunchPad board. Note that we have a version of the third scenario that uses a MAX3232 driver chip (you can see this chip in the Cybot baseboard schematic, photo, or actual board near the DB9 serial socket). Sketch your own version of the third scenario, similar to that shown in the video. Your sketch should specify UART1 and the actual GPIO port pins used to communicate with the PC in the lab. 5

Answer the remaining prelab questions, 8 - 10. 8. I/O synchronization behavior Read section 11.1, I/O Synchronization, in the VYES book, stopping before Interactive Tool 11.3 http://users.ece.utexas.edu/~valvano/Volume1/E-Book/C11_SerialInterface.htm (note that the interactive tools in this chapter may only work in the Firefox browser, and if so, ignore them). Read about the synchronization mechanisms shown in figures 11.1 and 11.2. See also Figure 12.2 from the VYES book, which shows the third (interrupt) mechanism as well as how a main program executes other tasks. Instead of polling (i.e., waiting in a loop) to receive data, an interrupt approach can be used. This lets the main program do other tasks. A separate interrupt handler function (interrupt service routine, ISR) is executed whenever a character is received by a UART. The main program doesn’t have to busy-wait and instead just gets data when it needs it. 6

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For example, think about an analogy of a classroom: suppose the instructor is like a processor executing a main program of teaching, including receiving student questions. Briefly explain the difference between polling and interrupts with this or another similar analogy. For example, explain how the instructor receives questions in relation to doing other tasks when a) polling, or b) using interrupts. Polling – the teacher will wait for questions to answer and then answer as they show up Interrupt – the teacher continues along until interrupted by a question to answer and then goes back to what they were doing 9. I/O synchronization - UART registers Consider some of the UART registers used when programming the mechanisms shown in question 8. UART Data (UARTDR): UARTx_DR_R UART Flag (UARTFR): UARTx_FR_R UART Interrupt Mask (UARTIM): UARTx_IM_R UART Raw Interrupt Status (UARTRIS): UARTx_RIS_R UART Masked Interrupt Status (UARTMIS): UARTx_MIS_R UART Interrupt Clear (UARTICR): UARTx_ICR_R Refer to VYES Figure 11.1. Assume we are using UART1 as in Lab 6. Identify one register from the list above for each question below. A register will be used for only one answer. a. Which register would be read in the “Read data” box in Figure 11.1? UART Data (UARTDR): UARTx_DR_R b. Which register would be tested in the “Status” decision box in the figure? UART Flag (UARTFR): UARTx_FR_R c. Which register indicates that there has been a trigger for an interrupt, such as receiving a character into the UART (one of the conditions necessary to get to the “Interrupt” in the figure)? UART Raw Interrupt Status (UARTIS): UARTx_RIS_R d. Which register is set during initialization to allow (or enable) an interrupt signal from the UART (one of the conditions necessary to get to the “Interrupt” in the figure)? UART Interrupt Mask (UARTIM): UARTx_IM_R 7

10. UART Interrupt Mask Register Refer to the UARTIM register description in the Tiva datasheet. Refer to the macro definition for the UART1 Interrupt Mask register in the header file, tm4c123gh6pm.h. d. Write the full #define macro definition as given in the header file. #define UART1_IM_R (*((volatile unsigned long *)0x4000D038)) e. Write the line of code for the IM register to enable RX interrupts from the UART1 device. UART1_... UART1_IM_R | = 0b0000000000010000 UART1_IM_R | = 0x10 8