I developed an universal SPI driver for XMEGA line of MCU for a battery powered device, where power efficiency was important. To get anything started on new hardware I have started with a simpler code first which uses interrupts and then I began looking at using XMEGA’s DMA controller (that was totally new to me) to improve speed and make the MCU sleep longer. This is a complete driver that can work with any kind of SPI peripherals.

It is also a nice practical introduction to DMA, because XMEGA DMA controller is one of the most simple you can find in microcontrollers (comparing let’s say to Kinetis Cortex-M), yet has all the necessary features.
Continue reading “XMEGA high-performance SPI with DMA” →

Character LCD are one of the easiest and cheapest way of adding output to a microcontroller system. The world of character LCDs has mainly standarized on HD44780 controller chip, which was designed to be interfaced with the rest of the system by a parallel bus, but today simple bit-banging does the job.

One of the obstacles to using HD44780 with XMEGA are different supply voltages. Displays usually require 5V, while XMEGA is 3,3V-only. Continue reading “XMEGA and HD44780 LCD” →

Embedded systems often require permanent storage of some configuration parameters eg. radio channel, volume in a radio etc. All settings must be saved and read reliably, otherwise the device may become unpredictable. Imagine a variable frequency drive (an “electric motor controller”) set to a certain speed, that after a power cut reads bad data from it’s memory and overspeeds an expensive piece of moving machinery leading to physical damage.
Continue reading “Reliable storage of settings in EEPROM” →

CRCs are useful for checking if data received from outside or read from memory is not corrupted. This is especially important in embedded systems, as it could take just a single bit-flip to drastically change the configuration of the system. I needed to protect configuration structure of my new project when it is being saved and read from EEPROM. To make sure that the data I read from EEPROM is exactly what I have written I decided to use CRC-16 CCITT across the whole structure.

Continue reading “Using XMEGA hardware CRC generator for CRC-16 CCITT” →

Fuses in AVR microcontrollers have a bad reputation among beginners, because a wrong setting can lock you out of accessing the chip. With the right tools they are not scary. 🙂

Fuses are just a special name for three bytes of EEPROM-like memory (they are not “conventional OTP” fuses at all) that set the most low-level features of an AVR like:
Continue reading “AVR fuses for beginners” →