The Top 25 ATtiny Interview Questions for Embedded Systems Jobs

Landing an embedded systems job often requires mastery of microcontroller programming. ATtiny microcontrollers from Microchip are a popular choice for many embedded applications. As such expect ATtiny-related questions if you’re interviewing for an embedded software role.

In this article, we’ll explore the top 25 ATtiny interview questions and sample answers to help you ace your next job interview Whether you’re a hobbyist tinkerer or a seasoned professional, understanding the key concepts behind these tiny yet mighty chips is essential

1. Compare ATtiny Microcontrollers to Arduino and Raspberry Pi

Frequency of Entities:
attiny: 4
arduino: 2
raspberry pi: 2

Arduino, Raspberry Pi and ATtiny are all microcontroller platforms, but with varying complexity, size, cost and use cases:

• ATtiny – Family of low power compact 8-bit AVR microcontrollers made by Microchip. Well-suited for simple embedded applications.

• Arduino – Open source electronics platform based on ATmega MCUs. More powerful than ATtiny with built-in support for peripherals.

• Raspberry Pi – Credit card-sized single board PC capable of running Linux. Most complex and flexible option, but also more expensive and power hungry.

2. Program an ATtiny Chip Using Arduino as ISP

Frequency of Entities:
attiny: 3
arduino: 3

To program an ATtiny with Arduino as the in-system programmer (ISP):

1. Connect Arduino to computer and upload the ArduinoISP sketch.

2. Wire up ATtiny to Arduino based on pinout for the ATtiny model.

3. In Arduino IDE, select ATtiny board, processor and clock speed.

4. Under Programmer, choose Arduino as ISP.

5. Write sketch compatible with ATtiny’s resources.

6. Upload using Sketch > Upload Using Programmer.

The Arduino will compile and flash the program to the ATtiny via SPI.

3. Coding Considerations for the ATtiny

Frequency of Entities:
attiny: 3

When writing code for ATtiny microcontrollers:

• Optimize for the limited memory and flash storage.

• Avoid memory-hungry libraries.

• Use pin-efficient techniques like multiplexing.

• Account for lower maximum clock speed.

• Ensure your development environment supports ATtiny programming and debugging.

Tight resources on ATtiny forced careful, efficient code. Plan pin usage, memory allocation and timing factoring the target chip specs.

4. The Role of Watchdog Timers in ATtiny

Frequency of Entities:
attiny: 3
watchdog timer: 2

The watchdog timer (WDT) on ATtiny chips provides:

• An independent timer to recover from crashes.

• System reset generation if software fails to periodically service WDT.

• A way to escape infinite loops and hangs.

For example, in a weather station project, I used the WDT to sleep and periodically wake the ATtiny for sensor sampling. If the chip hangs, the WDT timer reset lets it resume operation.

5. Optimizing Power Consumption on ATtiny

Frequency of Entities:
attiny: 2

Strategies to minimize power consumption on ATtiny include:

• Using sleep modes when idle.

• Disabling unused modules.

• Choosing lower clock frequencies if possible.

• Operating at the lowest suitable supply voltage.

• Writing efficient code to reduce unnecessary computation.

The ATtiny’s event-driven sleep modes, paired with careful configuration and coding, enable low-power battery operation.

6. Interfacing with ATtiny via SPI

Frequency of Entities:
attiny: 2
spi: 4

To use the SPI interface on ATtiny:

1. Configure pins – Set MOSI, MISO, SCK, SS as outputs.

2. Initialize SPI Control Register for mode, clock rate, etc.

3. Enable SPI in master mode.

4. Write transmit data to the data register to start transmission.

5. Wait for transfer complete flag.

6. Read received data from the data register.

SPI provides synchronous serial communication with peripherals like sensors, SD cards, etc.

7. Example of a Complex Project with the ATtiny

For a weather station project, I used an ATtiny85 with the challenges of:

Frequency of Entities:
attiny: 2
weather station: 3
memory: 1

• Very limited memory – just 8KB flash and 512 bytes RAM.

• Difficulty implementing algorithms within memory constraints.

• Optimizing power consumption for battery operation.

To address the memory issue, I used bitwise operators, reduced variables, and efficient data structures. For power, I leveraged sleep modes and timed wakeups while maintaining timing accuracy. Despite its minimal resources, with careful coding the ATtiny85 proved capable of impressive functionality.

8. Built-in vs External ADCs with ATtiny

Frequency of Entities:
attiny: 2
adc: 4

Advantages of ATtiny’s built-in ADCs:

• Integration reduces complexity and saves PCB space.

• Faster conversion than external ADCs through direct data bus access.

However, external ADCs offer:

• Higher resolution and sampling rates.

• Better linearity and lower noise.

So if precision measurements are needed, an external ADC may be preferable. Otherwise the internal ADC saves money and PCB area.

9. Using PWM on ATtiny Microcontrollers

Frequency of Entities:
attiny: 2
pwm: 4

To utilize PWM on ATtiny chips:

1. Configure the TCCRx timer/counter registers for the desired PWM mode.

2. Set prescaler value through CSxx bits to scale the PWM frequency.

3. Define output compare behavior via COMxx bits to enable PWM output.

4. Adjust duty cycle by writing to OCRx registers. Higher OCRx values increase the PWM high time.

PWM outputs on ATtiny are useful for controlling motors, dimming LEDs, generating analog voltages, and more.

10. Debugging Code on an ATtiny

Frequency of Entities:
attiny: 2
debugging: 2

Debugging options for ATtiny include:

• Using a hardware debugger like Atmel-ICE which connects via JTAG or debugWIRE interfaces.

• Adding print statements to output key variables over serial connection to computer.

• Using an oscilloscope or logic analyzer to monitor pin states and timing.

• Simulating code execution on the ATtiny in Atmel Studio before deploying to physical chip.

• Ensuring your code is modular and readable for easier troubleshooting.

Debugging ATtiny poses challenges due to limited resources and interfaces. A combination of simulation, instrumentation, debugging hardware and good practices help.

11. Handling Interrupts on ATtiny

Frequency of Entities:
attiny: 1
interrupts: 4

To handle interrupts on ATtiny:

• Define ISR routines to run when specific interrupts trigger.

• Set/clear corresponding bits in interrupt mask registers to enable/disable interrupts.

• Use interrupts for timely response to events like sensor data updates, ADC conversions completion etc.

• Keep ISR code concise, avoid delay() and minimize variables shared with main program.

Interrupts make ATtiny suitable for real-time embedded applications by quickly responding to asynchronous external or internal events.

12. Interfacing ATtiny with Other Devices

Frequency of Entities:
attiny: 2

Interfacing the ATtiny with other devices involves:

• Using its GPIOs configured as digital inputs or outputs.

• Implementing communication protocols like I2C, SPI using dedicated hardware or bit-banged in software.

• Connecting analog sensors to ADC input pins and reading digitized values.

• Driving actuators like motors via PWM outputs.

• Triggering interrupts on state changes on input pins.

With a basic understanding of digital and analog I/O techniques, the diminutive ATtiny can interact with an amazing variety of electronics.

13. Addressing ATtiny Limitations in Projects

Frequency of Entities:
attiny: 2

When working within the ATtiny’s constraints:

• Use multiplexing and shift registers to expand limited I/O pins.

• Minimize memory usage through efficient coding and avoiding libraries.

• Implement bootloader for field firmware updates within small code space.

• Leverage prototyping boards and perfboards for interfacing, before designing custom PCB.

• Extensively simulate code on PC before deployment to reduce debugging time.

• Adopt a modular, iterative approach