![]() ![]() The AVR doesn’t overlap instructions, the ARM does. The much more complex ARM instructions, makes cycle counting harder. Note that cycle counting AVR instructions is easy. You could use external latches clocked off of an atomic clock to reduce the jitter here too. ![]() The timing precision there would probably be limited by the logic between the CPU and GPIO pins. On the other hand, software running on the Raspberry Pi bare metal, would be running about 70 instructions for every one instruction on the atomic clock controlled Arduino. If you need more precision, you might want to add some external latches that are clocked directly off of the atomic clock. You can check the AVR data sheet to see the timing details on the I/O pins. So you need a bit of code to detect that single cycle slop, and correct for it, otherwise, you’ve wasted $400 on your atomic clock. An interrupt during a two cycle instruction would be 100ns later. Note that instructions on the Arduino take one or two clock cycles. Such an Arduino would be slower than ones with a 16Mhz ceramic resonator or the ones with a 16.000Mhz crystal, but the jitter would be hard too measure. Many atomic clock modules have a 10.000000Mhz output which could be suitably buffered and used instead of the Arduino’s crystal. However, for applications, where the goal isn’t to learn how to write a device driver, most people will probably just use an Arduino, bare AVR chip, or other microcontroller for the actual real time bit twiddling, even after it becomes well documented. Even the peripherals that are connected “directly” to the CPU, like the GPIO pins, are connected with packetized busses, so the timing is more complex than on an Arduino.īecause the Raspberry Pi is inexpensive, mass produced, and will be widely available, it will be a good choice for learning how to write device drivers in Linux. ![]() To access those in new ways, requires new GPU code (which we lack the tools and information to write). To further complicate things on the Raspberry Pi, some peripherals are connected to the GPU. Not a good first project for a 17 year old. Then you need a bunch of infrastructure to manage the communication between your driver and userspace, plus all the initialization. One common technique for low jitter realtime stuff, in simpler embedded Linux systems, is to do the most timing sensitive parts in the bottom half of a device driver, the less timing sensitive parts in the top half of a device driver. (But, you can get it to mess up the audio, or lose mouse events, if you get enough other stuff going on at high enough priority.) Plenty of Linux systems with far less resources than the Raspberry Pi manage to do audio and video without skipping, but it took a lot of effort to make that work right. The Raspberry Pi does that stuff already. It is impossible on any multiuser/multitasking system to do tasks with realtime constraints, such as track a mouse in a window system, record or playback audio, or play HD videos at 1080P without skipping… Usually, an Arduino is running just one program at a time, often without interrupts. ![]() With the stock software, a Raspberry Pi is running a multiuser/multitasking operating system. I’m looking forward to see the types of applications the Pi-Duino Community creates. For those who may be interested I’ve included a matrix comparing the two platforms’ various attributes: I have to agree that pairing the Raspberry Pi with the Arduino Uno will help to unleash a lot of creative ideas on how to use these two systems together. I do not like that term at all.) So here’s to a happy partnership between the two boards – I hope they’ll be good friends! Ultimately, we hope that successful sales of Raspberry Pi will encourage people to buy Arduinos too, and vice versa: the two have what I believe business school-types call “good synergy”. Prototype schematics and layout are on his website already do go and have a look. It’s currently in development, and it’ll be open hardware when he’s done with it. This is incredibly exciting for us, given the enormous range of shields that are out there in the ecosystem already (I think the number stands at about 280 at the moment). You can either use it as a link between your Arduino and your Raspberry Pi, or use it to connect Arduino shields directly to your Raspi. Meanwhile, Omer is working on a new device called Ponte, which acts as a bridge between Raspberry Pi and Arduino or its shields. There are instructions on his blog, which seasoned Arduino hackers should find easy enough to follow. Simon Monk has been getting his Raspberry Pi and Arduino talking using Python. ![]()
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