Raspberry Pi User Guide. Eben Upton

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СКАЧАТЬ to the original 8-bit microcomputers. It was hard to imagine these machines capturing the imaginations of kids used to modern games consoles and iPads.

      There had been discussions at the University Computer Lab about the general state of computer education, and when I left the Lab for a non-academic job in the industry, I noticed that I was seeing the same issues in young job applicants as I’d been seeing at the University. So I got together with my colleagues Dr Rob Mullins and Professor Alan Mycroft (two colleagues from the Computer Lab), Jack Lang (who lectures in entrepreneurship at the University), Pete Lomas (a hardware guru), and David Braben (a Cambridge games industry leading light with an invaluable address book), and over beers (and, in Jack’s case, cheese and wine), we set up the Raspberry Pi Foundation – a little charity with big ideas.

      Why “Raspberry Pi”?

      We get asked a lot where the name “Raspberry Pi” came from. Bits of the name came from different trustees. It’s one of the very few successful bits of design by committee I’ve seen, and to be honest, I hated it at first. (I have since come to love the name, because it works really well – but it took a bit of getting used to since I’d been calling the project the “ABC Micro” in my head for years.) It’s “Raspberry” because there’s a long tradition of fruit names in computer companies (besides the obvious, there are the old Tangerine and Apricot computers – and we like to think of the Acorn as a fruit as well). “Pi” is a mangling of “Python”, which we thought early on in development would be the only programming language available on a much less powerful platform than the Raspberry Pi we ended up with. As it happens, we still recommend Python as our favourite language for learning and development, but there is a world of other language options you can explore on the Raspberry Pi too.

      In my new role as a chip architect at Broadcom, a big semiconductor company, I had access to inexpensive but high-performing hardware produced by the company with the intention of being used in what were then very high-end mobile phones – the sort with the HD video and the 14-megapixel cameras. I was amazed by the difference between the chips you could buy for $10 as a small developer, and what you could buy as a cell-phone manufacturer for roughly the same amount of money: general purpose processing, 3D graphics, video, and memory bundled into a single BGA package the size of a fingernail. These microchips consume very little power, and have big capabilities. They are especially good at multimedia, and were already being used by set-top box companies to play high-definition video. A chip like this seemed the obvious next step for the shape the Raspberry Pi was taking, so I worked on taping out a low-cost variant that had an ARM microprocessor on board and could handle the processing grunt we needed.

      We felt it was important to have a way to get kids enthusiastic about using a Raspberry Pi even if they didn’t feel very enthusiastic about programming. In the 1980s, if you wanted to play a computer game, you had to boot up a box that went “bing” and fed you a command prompt. It required typing a little bit of code just to get started, and most users didn’t ever go beyond that – but some did, and got beguiled into learning how to program by that little bit of interaction. We realised that the Raspberry Pi could work as a very capable, very tiny, very cheap modern media centre, so we emphasised that capability to suck in the unwary – with the hope that they’d pick up some programming while they’re at it.

      After about five years’ hard grind, we had created a very cute prototype board, about the size of a thumb drive. We included a permanent camera module on top of the board to demonstrate the sort of peripherals that can easily be added (there was no camera when we launched because it brought the price up too much, but we’ve now made a separate, cheap camera module available for photography projects), and brought it along to a number of meetings with the BBC’s R&D department. Those of us who grew up in the UK in the 1980s had learned a lot about 8-bit computing from the BBC Microcomputer and the ecosystem that had grown up around it – with BBC-produced books, magazines and TV programmes – so I’d hoped that they might be interested in developing the Raspberry Pi further. But as it turned out, something has changed since we were kids: various competition laws in the UK and the EU meant that “the Beeb” couldn’t become involved in the way we’d hoped. In a last-ditch attempt to get something organised with them, we ditched the R&D department idea and David (he of the giant address book) organised a meeting with Rory Cellan-Jones, a senior tech journalist, in May 2011. Rory didn’t hold out much hope for partnership with the BBC, but he did ask if he could take a video of the little prototype board with his phone, to put on his blog.

      The next morning, Rory’s video had gone viral, and I realised that we had accidentally promised the world that we’d make everybody a $25 computer.

      While Rory went off to write another blog post on exactly what it is that makes a video go viral, we went off to put our thinking caps on. That original, thumb-drive-sized prototype didn’t fit the bill: with the camera included as standard, it was way too expensive to meet the cost model we’d suggested (the $25 figure came from my statement to the BBC that the Raspberry Pi should cost around the same as a text book, and is a splendid demonstration of the fact that I had no idea how much text books cost these days), and the tiny prototype model didn’t have enough room around its periphery for all the ports we needed to make it as useable as we wanted it to be. So we spent a year working on engineering the board to lower cost as much as possible while retaining all the features we wanted (engineering cost down is a harder job than you might think), and to get the Raspberry Pi as useable as possible for people who might not be able to afford much in the way of peripherals.

      We knew we wanted the Raspberry Pi to be used with TVs at home, just like the ZX Spectrum in the 1980s, saving the user the cost of a monitor. But not everybody has access to an HDMI television, so we added a composite port to make the Raspberry Pi work with an old cathode-ray television instead. Since SD cards are cheap and easy to find, we chose them as our storage medium: the original Model A and Model B used full-size cards, while more recent iterations have moved to the now more common microSD standard. And we went through several iterations of power supply, ending up with a micro USB cable. Recently, micro USB became the standard charger cable for mobile telephones across the EU (and it’s becoming the standard everywhere), which means the cables are becoming more and more ubiquitous, and in many cases, people already have them at home.

      By the end of 2011, with a projected February release date, it was becoming obvious to us that things were moving faster, and demand was higher, than we were ever going to be able to cope with. The initial launch was always aimed at developers, with the educational launch planned for later in 2012. We had a small number of very dedicated volunteers, but we needed the wider Linux community to help us prepare a software stack and iron out any early-life niggles with the board before releasing into the educational market. We had enough capital in the Foundation to buy the parts for and build 10,000 Raspberry Pis over a period of a month or so, and we thought that the people in the community who would be interested in an early board would come to around that number. Fortunately and unfortunately, we’d been really successful in building a big online community around the device, and interest wasn’t limited to the UK, or to the educational market. Ten thousand was looking less and less realistic.

      Our Community

      The Raspberry Pi community is one of the things we’re proudest of. We started with a very bare-bones blog at www.raspberrypi.org just after Rory’s May 2011 video, and put up a forum on the same website shortly after that. That forum now has more than 170,000 members – between them they’ve contributed nearly a million posts of wit and wisdom about the Raspberry Pi. If there’s any question, no matter how abstruse, that you want to ask about the Raspberry Pi or about programming in general, someone there will have the answer (if it’s not in this book, you’ll find it in the forums).

      Part of my job at Raspberry Pi involves giving talks to hacker groups, computing conferences, teachers, programming collectives, and the like, and there’s always someone in the audience who has talked СКАЧАТЬ