BeagleBone Black GPIO Benchmark

Look what the mailman brought: It’s a shiny (or maybe matte?) BeagleBone Black, freshly arrived (actually it’s been over a month, but time sure flies…) from Newark element14! I’ve been doing Raspberry Pi related hacking for a while, but especially when the Pi was still fresh and new, I did from time to time consider if the grass would be greener on other side of the fence. Or blacker, in this case, as I mean BeagleBone Black.

BeagleBone was long very much more powerful than Raspberry Pi, but now that Pi2 has come out, price and specification-wise they are closer than ever. A quick personal comparison chart:

  BeagleBone Black Raspberry Pi 2 (B)
Price 46 € (Element14) 32 € (Element14)
Processor 1GHz single-core Cortex-A8 0.9GHz quad-core Cortex-A7
Memory 512MB DDR3 1GB
Connections USB host, USB device, micro-HDMI 4x USB, HDMI, 3.5mm Audio/analog video
GPIO 2x 46 pin headers (65 digital I/O) 40 GPIO pins (26 digital I/O)
Other 4GB integrated flash, works as USB device camera and display interface on board

When Pi1 was out, the BeagleBone Black with the more modern Cortex-A8 chip and higher clockrate was definitely the more powerful, but now with 4-core Pi2, the tables have somewhat turned. Still, the clockrate is higher and there’s more GPIO. And speaking of GPIO, my Raspberry Pi vs. Pi2 GPIO benchmark has gotten a lot of interest, so I thought the best way to take this black beauty for a test drive would be to benchmark BeagleBone Black GPIO in a similar way.

Test setup

Test bench

The test subject is the most recent revision C of BeagleBone Black. I followed the (a bit lacking in detail and readability) Getting Started guide and downloaded the latest Debian Jessie image (8.3, 2016-01-24), flashed it to card and ran apt-get update and apt-get dist-upgrade (2016-04-14).
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Adafruit Trinket USB keyboard without Arduino

Happy New Year 2016! After a long hiatus in electronics, I have been quite busy in the last month or so. I have a bigger (USB MIDI related) project posting coming up, but just wanted share a small nugget already.

I ordered a big chunk of things recently from Adafruit shop and Sparkfun. Among them was the lovely Adafruit Trinket (which actually came as a free bonus because I spent way too much on black friday :).

Now I am planning a project which involves transforming the very compact, but already USB-enabled Trinket into a USB MIDI device. However, there are two problems:

  1. Adafruit examples for USB come in Arduino form
  2. There are no USB MIDI examples

I somewhat dislike the high-level Arduino environment in cases where low-level performance is needed (and the V-USB implementation is one of those places), and for my later MIDI part, I will need fine-grained control to juggle serial communication and USB. Also, all USB MIDI examples are on “bare metal”, so the Adafruit example Arduino code would require deeper knowledge of Arduino inner workings than I have.

Time to do some chopping!

Slimming Down the TrinketKeyboard Example

I decided to adapt the excellent base code in Adafruit Trinket USB GitHub repository, but trim the keyboard example to bare essentials (my next step will be to transform it into a USB MIDI device, so the less code I have to adapt, the better). Turns out this was quite simple to do:
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Super Simple 50+ kHz Logic Analysis with ATtiny2313 and FTDI Friend

AVR & FTDI logic analyzer

While banging my head against the wall with debugging my PS/2 keyboard thingy, I really wished I had a dedicated logic analyzer (preferably with PS/2 decoder, but even raw binary data would’ve been fine). So I decided to try out a long hatched idea – combine an ATtiny2313 and FTDI for some unlimited-length logic capturing with a PC. You’ll only need:

  1. ATtiny2313
  2. 20 MHz crystal and caps (slower will also work, frequency just defines what baud rates you’ll achieve)
  3. FTDI USB/serial converter, like the FTDI friend from Adafruit
  4. Optionally, some power-stabilizing capacitors, reset pullup and ISP programming header for flashing the firmware

ATtiny2313 is ideal for this, as it has all eight port B pins on one side in numerical order – attaching up to 8 logic lines is really straightforward. With 20 MHz crystal, baud rates close to 1 Mbps can be achieved in fast serial mode. I used Adafruit’s FTDI Friend for really simple (and way faster than most cheap serial adapter dongles) serial to USB conversion – just connect ATtiny RXD pin to TX, and TXD to RX, and you can even get power from the Friend so you’re all set! For crystal and that other stuff, see my ATtiny2313 breadboard header post for schematic, the picture above should fill you in with the rest.

Firmware code

This device has some of the smallest firmware codebases ever (firmware is 128 bytes). All we need to do is to set up UART with desired speed, and have the AVR chip to fire up an interrupt whenever data has been sent, and then use that to send current state of port B (using PINB):

#include <avr/io.h>
#include <avr/interrupt.h>

void USARTInit(unsigned int ubrr_value, uint8_t x2, uint8_t stopbits) { 
  // Set baud rate
  UBRRL = ubrr_value & 255; 
  UBRRH = ubrr_value >> 8;

  // Frame Format: asynchronous, 8 data bits, no parity, 1/2 stop bits
  UCSRC = _BV(UCSZ1) | _BV(UCSZ0);
  if(stopbits == 2) UCSRC |= _BV(USBS);

  if(x2) UCSRA = _BV(U2X); // 2x

  // USART Data Register Empty Interrupt Enable

  // Enable The receiver and transmitter

int main() {
  // 230.4 kbps, 8 data bits, no parity, 2 stop bits
  USARTInit(10, 1, 2); // replace 10 with 4 to get 0.5 Mbps

  sei(); // enable interrupts

  while(1) {}
  return 1;


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Breakout Bonanza and DS1307 Realtime Clock

As if I didn’t have enough things on my “to try when I have the time” list already, I recently did a little shopping in both Adafruit and SparkFun. Both had several nifty breakout boards available that promised to speed up and streamline my breadboard projects a lot. In addition to some SMD breakouts that are still in their sealed bags, here’s what I got:

I had a lot of fun soldering the breadboard headers to these little guys. Many are for future projects, like the frequency generator which I’m planning to use for some RFID experiments, and some are just to avoid stripping apart stuff like the connector breakouts. As today’s main topic, I’m covering the DS1307 realtime clock (RTC) breakout in more detail. If you are interested in some of the other items, drop me a comment and I’ll get back to it!

DS1307 Realtime Clock

A realtime clock is simply something that keeps record of the time. Usually, these types of clocks are paired with a small coin cell battery that enables them to keep on counting even if the rest of the circuit is powered of. Such is the case with this breakout, too. Adafruit has an excellent tutorial covering the assembly of this device, all you need is some solder and an iron.

After getting it together, it took me a while to get it working. I used Bus Pirate to communicate with the chip, with the following connections:
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