Lab 0: Introductory Lab, Rev D

Transcription

1 Lab 0: Introductory Lab, Rev D I. INTRODUCTION This lab is to familiarize students with the tools required to compile and download C code to the UM003 microcontroller board. It is also intended to ensure students have the prerequisite knowledge of C to build embedded code. At the end of the lab students should have all the necessary tools, drivers and patches downloaded to build and execute C programs. Students should be able to successfully write simple code in C to blink an LED. This lab is also intended to refresh the student s memory of pointers and gain familiarity with programming the ATMega128. II. DOWNLOADS To compile C code for the Atmel microprocessor students will need WinAVR, a gnu-c programming environment for the Atmel AVR microprocessor series, which can be obtained at Click on downloads on the left side of the page. This will direct you to a new webpage where the most current version can be downloaded. Select the WinAVR package and follow the prompts to download and install WinAVR. This package includes Programmers Notepad which is what should be used for all labs. WinAVR is a customized version of avr-gcc for Windows. WinAVR includes Programmer s Notepad, which is the integrated development environment (IDE) we will use to compile the C code for this class. AVRStudio is another IDE from Atmel, the developer of the ATMega128. We will use AVRStudio only to download executable code (in the form of hex files) to the UM003 development board. Students will need the latest version of both AVRStudio and the AVRStudio Service Pack. Presently, these are AVR Studio 4.18 (build 684) and AVR Studio 4.18 SP2 (build 700) and can be found here, You will need to register to download the AVR Studio. NOTE for Vista 64-bit users only and AVR Studio 4.15 (not sure if this applies to 4.18): There is a patch students will need to download to be successful in compiling code. Without the patch students will get an error such as sync_with_child or something similar. The download for the patch can be found at Scroll all the way to the bottom of the page and at the top of the screen students will see a paragraph that starts with If students are using Vista 64-bits. Ignore the comment that the latest version of AVR has the patch included. Students will need the patch even with the latest version of WinAVR. Students will need to extract the msys-1.0-vista64.zip to the following location: C:\WinAVR \utils\bin. Students will need to rename the existing msys-1.0dll to something else to save for recovery if needed. NOTE: If students are using Vista 32-bit, a patch may or may not be needed. If students get an error such as sync_with_child or something similar students will need to follow the instructions for the VISTA 64-bit users. A link to the ATMega128 user guide and the schematic for the UM003 board can be found on the class website under the link PBO/RT Help. III. Using Pointers and Volatile Variables If students are not familiar with pointers, they should refer to the various tutorials on the web or consult a textbook on C programming. C programming is a prerequisite of this class. The instructors are happy to help students, but it is not the intent of this lab to teach pointers. This section is only for review.

2 A pointer is an address to a memory location. Anything that resides in memory has an address associated with it. Variables reside in memory, as do arrays, and functions. Therefore, variables, arrays and functions can all have pointers declared that point to them. For embedded systems, registers, memory-mapped I/O and other hardware components can also have pointers declared that point to them since they have addresses associated with them. When students declare a variable, for example, with the statement: int var; /* declare an integer variable */ students are setting aside (allocating) memory for the variable var with the number of bytes reserved for an int. To find out the address of these reserved bytes, we use the address of operator &, which returns the address (the pointer ) to the variable: &var; /* returns the address of var */ It is also possible to declare a pointer variable with the statement: int *varpointer; /* declare a pointer variable */ The * character is the value of operator. It indicates students are declaring a pointer variable for an address that points to an int. varpointer is a variable that students can use to hold an address that points to an int, it does not hold a data value. For example, students can use it to hold the address (the pointer) to var with the statement: varpointer = &var; /* varpointer now points to var */ To read the value of var, students can use the value of operator, *, to get the value that a pointer points to: *varpointer; /* returns the value of var */ It is important to realize that when students declare a pointer variable students are not actually reserving memory to hold a value. Students must always initialize the pointer to point to some valid region of memory before students try to access the value of the pointer. For example, the following code will cause an error (though the effects of the error may not be immediately apparent): int *varpointer; /* declare a pointer variable */ *varpointer = 10; /* set the value of varpointer to 10 */ The code above is erroneous because varpointer is not initialized to point to a valid memory location. It may be pointing to something, but students don t know what. Therefore, students are writing the value 10 to some unknown location. If students declare an array variable, for example, with the statement: int vararray[10]; students can retrieve the address of the beginning of the array in one of two ways:

3 varpointer = vararray; /* get addr of vararray */ varpointer = &vararray[0]; /* get addr of vararray[0] */ In both cases, varpointer points to (is the address of) the first element of the array. Likewise, if students declare a function, for example, with the following code fragment: int func5() { return (5); } students can retrieve the address of the function with just its name: varpointer = (int *) func5; /* get addr of func5() */ In the case above, varpointer is declared as a pointer to an int, not a pointer to a function that returns an int. Therefore, it is proper to type cast the pointer-to-a-function-that-returns-an-int to a pointer-to-an-int before storing it in a pointer-to-an-int variable. Even better, instead of using varpointer, students should declare a pointer-to-a-function-that-returns-an-int and store it there. For example if PortC was the variable that points to port C it must first be defined as a pointer as follows. volatile uint8_t *PortC_ptr; This defines PortC_ptr as a volatile pointer. The unit8_t type is an ATMEL-specific declaration for unsigned integer 8-bit. Then later in the code when PortC is used, the address must follow as this example shows. PortC_prt = (uint8_t *)0x40; //in this made up example, 0x40 is the address Recall that volatile variables are those whose value may change spontaneously or may be changed by an external entity. External devices which can change a variable s value can be those things which provide user input like a keyboard, or devices which can change based on the environment such as sensors. When a variable is not defined as volatile and it is changed by an external device, the program will not detect the changes made by the external device. The complier assumes only the program will change the value of the variable. If the desire is for the variable to change to reflect the external device, the variable must be defined as volatile. Like many other compilers, avr-gcc will attempt to optimize any code that it compiles. This may cause problems for code using simple loops to generate time delays. By declaring index variables as volatile, students will ensure that the compiler will not optimize away the delay loops students write. Try including volatile in the declaration of index variables and then removing it to see the difference. An oscilloscope can be used to verify the behavior of the LED when not using volatile variables. IV. BIT MASKING In this lab students must toggle an LED on and off. This LED is wired to a particular pin on the development board. The pin is part of an 8-bit port on the ATMega chip. Individual pins cannot be accessed singularly; instead the entire port must be accessed. Bit masking is used to change only one

4 pin in the port. As a refresher, remember that a value ORed with 0 will remain unchanged. A value ANDed with 1 will also remain unchanged. This can be used to ensure that only the desired pin is changed when turning on or off the LEDs. V. LED WIRING Figure 1 is a schematic of the UM003 development board. The circled portion is enlarged in Figure 2. If students compare this schematic to the one linked on the class webpage, students will notice that LEDs and resistors have been added for this class. Figure 1: UM003 schematic

5 Figure 2: LED schematic VI. PREPARATION Read the section I/O Ports of the ATmega128 user guide starting on page 66. On the course website under the link PBO/RT Help select ATmega128 to open the user guide for the CPU or UM003 to open the board schematic. Look up the memory map (register summary) for the ATMega128 on page 362 of the Atmel user guide. Find the relevant memory locations for Port B and Port E. These are found on the far left side of the chart and are in parentheses. (ATmega103 compatibility mode is shown outside of parentheses.) These addresses are required to blink the LEDs. In the lab write-up include the following. The ports needed to turn on and off the LEDs The location in memory (addresses) of the ports. What is the default state of the I/O ports? Input or output? Why would that be? VII. PROCEDURE With the knowledge gleaned from the User Guide, write a C program that blinks the red LED at 2 Hz and blinks the green LED at 1 Hz. Be sure to use pointers and bit masking to control the LED states so that only the bits that control the LEDs are toggled while all other bits remain unchanged. You must explicitly set the data directions and data values. DO NOT include avr/io.h and DO NOT USE the predefined macros in that file (PORTB, PORTE, DDRB or DDRE or any others) for this part of the lab.

6 Make sure to include inttypes.h, which defines the Atmel variable types. Use a stopwatch to measure the time for 30 blinks of each LED. If the LEDs do not blink at exactly 1 Hz and 2 Hz, adjust the code to get as close as possible. Include this source file as an appendix in the lab report. When in doubt, over-comment or risk losing points. You will be graded on commenting of your code. Include your measurements for the blink rate of each LED in your lab write-up. //Simple code outline #include <stdio.h> #include <inttypes.h> int main (void) { // Local variable declarations here // What should be volatile and what does not care? // Since this microcontroller has an 8-bit data path, don t use // ints. Use the special types defined in inttypes.h: // unit8_t and int8_t for 8-bit quantities, int16_t, int32_t, etc. } while(1){ { (/* toggle LEDs */) } { (/* include delay loops */) } { (/* toggle LEDs again as necessary*/) } } /* endwhile */ I recommend using WinAVR and Programmer s Notepad for compilation. The new version of AVR Studio includes a C compiler and is fully integrated. I have not tested object code compatibility with AVR Studio and future labs will involve linking compiled object files, which may not work with AVR Studio. You are welcome to try, however. VIII. DOWNLOADING CODE Once students have compiled their code using WinAVR and Programmer s notepad and are ready to download their code to the board, follow these steps. 1. Connect AVRISP to board. 2. Connect AVRISP to USB on computer. 3. Plug in power supply for board. Check for two green lights on programmer. 4. Open AVRStudio. The following figure will open. Select Cancel. It is not necessary to select a project, name or location.

7 Figure 3: Select AVR GCC 5. Select the small black AVR button shown in Figure 4. Figure 4: Select the small black AVR button 7. If AVR Studio 4.18 asks you to upgrade your ISP to version 1.12 or later, please do so. Beware of some previous versions as these can cause the AVRISP to fail to connect. This window can be seen in Figure 5.

8 Figure 5: Make sure to press CANCEL if Version 1.10 is available. 8. Look for OK at the bottom of the window under the Program tab. This means everything is communicating properly. 9. STUDENTS ONLY NEED TO DO THIS ONCE: Click on the fuses tab then click Read. Make sure the following items are as noted which are demonstrated in Figure 6: M103C is unchecked JTAGEN is unchecked SUT_CKSEL is set to Ext Clock startup time 6 ck + 4ms

9 Figure 6: Fuses tab on AVRISP setup 10. Under program tab follow these steps verify device is AtMega128 programming mode = ISP check Erase device check Verify device 11. Students are now ready to download code. In the Flash input box of the Program tab, specify the hex file to download Click Program Wait for the light on the ISP to flash green.

10 Note that there are ATMega-specific ways for declaring unsigned integer variables. For instance, unsigned 8-bit integers are declared with uint8_t, while 16-bit and 32-bit unsigned integers are declared with uint16_t and uint32_t, respectively. These are defined in the header file inttypes.h. IX. REPEAT USING ATMEL MACROS WinAVR pre-defines access to the registers of the ATmega128 through a collection of convenient macros. The point of the above exercise is to make sure we all understand how to access the microcontroller directly. From now on, we will use the pre-defined macros defined in avr/io.h. Repeat the LED code in section VII using the pre-defined macros in avr/iom128.h. (You will include avr/io.h, which automatically includes the proper header file, found at WinAVR/avr/include/avr. DO NOT INCLUDE avr/iom128.h explicitly.) With avr/io.h included, you may now use the macros such as PORTB and DDRB. Note how the macros in avr/iom128.h have the same names as the register names in the user guide. What does the code DDRA = 1 << DDA6 1 << DDA3; do? What are the alternate functions for Port F? How would you disable pull-up resistors for Port A if Port A was used as an input? X. SERIAL COMMUNICATION Students will now configure the setup for serial communication. The driver for the Acroname UART to USB chip can be found on the Silicon Labs website at the following location, Students may need to download the VCP Driver Kit appropriate for the operating system as can be seen in Figure 7. Once the VCP Driver Kit is downloaded and extracted, click on the icon to install the driver. When installing the driver, make sure to select, Launch the CP210x VCP Driver Installer as seen in Figure 8 below.

11 Figure 7: Selecting the appropriate VCP driver kit.

12 Figure 8: Make sure to select Launch the CP210x VCP Driver Installer NOTE for Vista 64-bit users: students must obtain hypertrm.exe and hypertrm.dll and install these onto the computer under C:\Windows\system32. The easiest way to get the hypertrm files is by coping them from a computer that is running XP. Open HyperTerminal located under Accessories\Communications. The Location information window will open. Enter 303 for the area code and press enter. The next window can be seen in figure 9. In this window choose a name as the communication port for the UM003. Students may also select an icon of their choosing (Vista users will not have this option). The next window is shown in Figure 10. The area code and phone number can be left blank. Students must, however, choose the correct port. With the board powered on and the USB cable connected to the computer and the brainstem (Acroname UART to USB chip), open the device manager. For Vista Users the device manager can be accessed just from the control panel. For XP users the path is control panel/system/hardware/device manager. As seen in Figure 11 under Ports students can see which port to select. In this example students can see COM5 is the port which talks to the Silicon Labs CP210x. The final figure, 12, shows the appropriate settings to communicate with the Acroname chip. Follow this example.

13 Figure 9: Hyperterminal connection description Figure 10: Hyperterminal connection window

14 Figure 11: Com port is located in the device manager (may just say USB )

15 Figure 12: Port settings Students will make use of serial communication in future labs. Here, only the setup is required. XI. DELIVERABLES On the course website students will find a lab report format. This format is what is expected for each lab. For this lab, only minimal requirements are included, but it is necessary to go through the exercise of completing the lab report to understand what is expected on future labs. Pay particular attention to commenting your code. Follow the Coding Style link on the website for more information. The questions asked in the body of the lab should be answered in the appropriate sections of the lab report. Upload your report to the Digital Drop Box on BlackBoard.