Raspberry Pi User Guide. Eben UptonЧитать онлайн книгу.
Pi 3
The latest model of Raspberry Pi to launch, the Raspberry Pi 3 (see Figure 1-5) builds on its predecessors with yet another new processor: the Broadcom BCM2837. The first to feature 64-bit, rather than 32-bit, support, the BCM2837 is significantly faster than the BCM2836 found in the Pi 2, which itself was a major upgrade from the BCM2835 of the original and Plus lineups. The Pi 3 is also the first model to get built-in wireless support, featuring a radio capable of connecting to 2.4 GHz Wi-Fi networks and Bluetooth devices.
FIGURE 1-5: The Raspberry Pi 3 board
As with the Raspberry Pi 2, though, little has changed with the layout: you'll find the same 40-pin GPIO header, four USB ports, 10/100 wired network port, and all other ports as with the previous models. The only wrinkle for compatibility is a minor change in the way the board communicates with certain add-on hardware; if you're unsure whether a device is compatible with the Raspberry Pi 3, contact the manufacturer or vendor before buying to ensure that software has been written with the change in mind.
A major advantage of the Raspberry Pi 3, beyond the improved performance and built-in wireless capabilities, is the 64-bit processor. Although little software exists to take advantage of this at present, a move to 64 bit promises to offer increased software compatibility, security, and performance over the 32-bit code the Raspberry Pi family runs today.
Raspberry Pi Zero
The Raspberry Pi Zero (see Figure 1-6) holds two accolades: it's by far the smallest Raspberry Pi, and it's by far the cheapest. Despite its size – roughly equivalent to a couple of sticks of chewing gum stacked one on top of the other – it loses little: the Pi Zero includes the same BCM2835 SoC and 512 MB of RAM as the Raspberry Pi Model B+, running at a slightly faster speed for improved performance.
FIGURE 1-6: The Raspberry Pi Zero board
Caveats apply to the use of the Pi Zero, however. Even compared to the Model A+, it’s cut down: the single micro-USB port and mini-HDMI port both require adapters before they can be connected to standard peripherals; the 3.5 mm AV jack is missing; there's no DSI port, and the CSI port requires an adapter; and the GPIO header, although present, requires pins to be purchased and soldered into place before it can be used.
If you are a Raspberry Pi beginner, the Pi Zero is not the best choice of starter board. When you're more experienced and are looking to add Pi-powered intelligence to embedded projects – especially where size, cost, and power draw are concerns – the Pi Zero should be the first board on your mind.
A Bit of Background
Before heading into Chapter 2, it's a good idea to familiarise yourself with some background details of the Pi and its creation. While the Pi is usable as a general-purpose computer, capable of performing the same tasks as any desktop, laptop, or server – albeit more slowly – it is designed as a single-board computer aimed at hobbyists and educational use, and as such differs from a “normal” computer in a couple of important ways.
ARM Versus x86
The processor at the heart of the Raspberry Pi system is a Broadcom BCM283x-series SoC multimedia processor. This means that the vast majority of the system’s components, including its central and graphics processing units along with the audio and communications hardware, are built onto that single component at the centre of the board.
It’s not just this SoC design that makes the BCM283x family different from the processor found in your desktop or laptop, however. It also uses a different instruction set architecture (ISA), known as ARM.
Developed by Acorn Computers back in the late 1980s, the ARM architecture is a relatively uncommon sight in the desktop world. Where it excels, however, is in mobile devices. The phone in your pocket almost certainly has at least one ARM-based processing core hidden inside. Its combination of a simple reduced instruction set computing (RISC) architecture and low power draw make it the perfect choice over desktop chips with high power demands and complex instruction set computing (CISC) architectures.
The ARM-based BCM283x family is the secret to the Raspberry Pi's capacity to operate on just the 5V power supply provided via the onboard micro-USB port. It’s also the reason why you won’t find any metal heat sinks on the device: the chip’s low power draw directly translates into very little wasted heat, even during complicated processing tasks.
It does mean, however, that the Raspberry Pi isn’t compatible with traditional PC software. The majority of software for desktops and laptops are built with the x86 instruction set architecture in mind, as found in processors from the likes of AMD, Intel, and VIA. As a result, it won’t run on the ARM-based Raspberry Pi.
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