I/O View and Other Bare-Metal Programming References

This section describes how you would typically write code in Studio 7, independent of a software configuration tool or framework, i.e. bare-metal. This is covered both as video (linked below) and hands-on document. The main focus is on each of the relevant programming references, how each is accessed, and what each is used for. The project context is to turn ON an LED, then blink with a delay. Although the ATtiny817 Xplained Pro is used the principles are general enough to use with any kit in Studio 7, though the principles apply to most devices supported in Studio 7.

Getting Started Topics

Video: I/O View and Bare-metal programming references

The list below is an overview of the programming references which are typically used. Particular emphasis is placed on I/O View, which provides a way to navigate data sheet register descriptions when editing or debugging, as well as to understand the current configuration when debugging. This second use of I/O view when debugging is also used to test new register configurations.

This topic is closely related to both Debugging 3: I/O View Memory View and Watch as well as Editor: Writing and Re-Factoring Code (Visual Assist).

In the process the following code is written. Although the code is simple, the decision process, using the list of programming references above, is described. 
#include <avr/io.h>
#define F_CPU 3333333
#include <util/delay.h>

int main(void)
{
	PORTB.DIR = PIN4_bm; 	

    while (1) 
    {
		_delay_ms(500);
		PORTB.OUTTGL = PIN4_bm;		
    }
}
Warning: Be sure to keep the #include <avr/io.h> line at the top of main.c. This header file will include the correct register map for the selected device, and without this statement, the compiler will not recognize any of the macros referenced in the code above.

Device Data Sheet (PDF)

Although I/O View allows easy access to navigate the data sheet at a register level, the PDF version still has a role. The device data sheet, in PDF format, tends to be used at least to get an understanding of the peripheral, through the block diagram and functional description. For example, to understand the PORT peripheral of the ATtiny817, we consulted the PORT Block Diagram and Functional Description > Principle of operation sections of the data sheet. These two sections together, connecting the description to the diagram, give a basic understanding of the PORT peripheral.
Figure 1. PORT Block Diagram from the PDF Data Sheet
Figure 2. Principle of Operation from the PDF Data Sheet of ATtiny817
Note: We used the device data sheet for the peripheral block diagram, as well as a description of the PORT DIR and OUT registers.

I/O View Data Sheet

Studio 7 allows to easily access the data sheet register descriptions by clicking F1 on the relevant register description. The HTML version of the data sheet opens online (by default). The data sheet will open in the context of the relevant register description.
Note: In this way we use the Data sheet from I/O View to understand that:
  1. 1.Writing a '1' to PORT.DIR[n] configures and enables pin n as an output pin.
  2. 2.If OUT[n] is written to '0', pin n is driven low.
Figure 3. Opening an Online Data Sheet from I/O View

I/O View (Debugging)

This functionality can directly be tested by starting a debug session, using Start Debugging and Break. So we are now able to begin testing functionality, as shown in the image below.
I/O View is covered in more detail in Debugging 3: I/O View Memory View and Watch.
Note: I/O View when debugging is used to:
  1. 1.Verify that writing a '1' to PORT.DIR4, sets pin as OUTPUT, LOW by default to LED turns ON.
  2. 2.Verify that writing a '1' to PORT.OUT4, turns OFF the LED.
Table 1. Atmel Studio Button Functionality (Programming and Launching Debug Sessions)
Button Functionality Keyboard Shortcut
Start Debugging and Break Alt + F5
Attach to Target  
Start Debugging F5
Break All Ctrl + Alt + Break
Start Without Debugging Ctrl + F5
Figure 4. Turning ON/OFF Kit LEDs Through Manipulating I/O View Registers when Debugging

Downloading Studio 7 Documentation

The data sheet can also be downloaded by using the Studio 7 help system. In this case, a similar functionality will work offline. This is described here: Downloading Offline Documentation.

Atmel Studio 7 Editor (Visual Assist)

The Studio 7 Editor, powered by Visual Assist has powerful features to help you write and refactor code, as well as easily navigate large projects. Suggestion functionality is shown in Figure 5, while an overview of the code navigation is shown in Figure 6. In the next section, Editor: Writing and Re-Factoring Code (Visual Assist), the editor features are covered in more detail.
Figure 5. Suggestion Functionality in the Studio 7 Editor for Writing Code
Figure 6. Atmel Studio 7 Editor Navigation Overview

Specifically in the video related to this section, the editor is used for the following.

Device Header Files

Through the Goto Definition functionality of the editor, it is easy to access the MCU device header files, i.e. by clicking on any register and then clicking on the goto button, or typing Alt+G. Writing PORTB. gives a suggestion list of potential registers, from the PORT structure, shown in figure Suggestion lists and the MCU device header files. For more information about how the AVR header files are structured, see AVR1000 for more information.

Figure 7. Suggestion lists and the MCU device header files

Kit Schematics and User Guide

The kit schematics and user guide are useful to understand the MCU pin connections on the kit. Full schematics and kit design files, such as Gerbers, are available on www.microchip.com, on the kit's product page.
Figure 8. How to Find Schematics for a Particular Development Board
The LED and button are connected to the pins as per the table below, from the ATtiny817 Xplained Pro User Guide.
Table 2. ATtiny817 Xplained Pro GPIO Connections
Silkscreen Text ATtiny817 GPIO Pin
LED0 PB4
SW0 PB5
The ATtiny817 Xplained Pro design documentation schematic shows the connections for the LED and button, as in the figure below.
Figure 9. ATtiny827 Xplained Pro GPIO Connection Schematics
From the schematics, it is concluded that:

AVR Libc

All the references covered to this point are just as relevant for SAM as for AVR, however, as the name suggests, this one is specific to AVR. AVR Libc is a Free Software project whose goal is to provide a high-quality C library for use with GCC on AVR microcontrollers. Together, avr-binutils, avr-gcc, and avr-libc form the heart of the Free Software toolchain for the AVR microcontrollers. Further, they are accompanied by projects for in-system programming software (avrdude), simulation (simulavr), and debugging (avr-gdb, AVaRICE).

The library reference is usually a quick interface into AVR Libc, as shown in Figure 10. One can quickly search the page for a relevant library. Relevant header files, which should be added to the project, are indicated in the module name. For example searching for 'interrupts', the relevant include will be #include <avr/interrupt.h>. Clicking into the module, a list of available functions and relevant interrupt callbacks can be found, as shown in Figure 11.

Figure 10. AVR Libc Library Reference
Figure 11. Using Interrupts with AVR Libc

Atmel START

Atmel START is a web-based software configuration tool, for various software frameworks, which helps you getting started with MCU development. Starting from either a new project or an example project, Atmel START allows you to select and configure software components (from ASF4 and AVR Code), such as drivers and middleware to tailor your embedded application in a usable and optimized manner. Once an optimized software configuration is done, you can download the generated code project and open it in the IDE of your choice, including Studio 7, IAR Embedded Workbench, Keil μVision, or simply generate a make-file.

Although Atmel START is a tool for MCU and software configuration, it can still be useful even in bare-metal development, i.e. writing code from scratch using the list of programming references described in this section. Creating a new project for the kit you are using, can be a useful alternative to the board schematic, using the PINMUX view. In addition, the CLOCKS view can be useful to check the default clocks of a device. Furthermore, viewing the configuration code, useful pieces can be pasted back into your project. For example, the AVR Libc delay functions require that the clock frequency is defined, as shown in Figure 14. For the ATtiny817 this default value would be: #define F_CPU 3333333.

Figure 12. Using START to Creating a New Project for a Relevant Board
Figure 13. Showing Board Labels in START as an Alternative to the Kit Schematic
Figure 14. Checking Default Clock Configuration and Using VIEW CODE to Find F_CPU Define
Parent topic: Getting Started