When a company chooses a CPU to be embedded, why are the typical choices PowerPC, ARM etc... Why not something like an AMD Athlon. On a similar vein to AMD processors, they seem to have embedded processors and the general consumer processors, why the difference? Finally, getting hold of the general CPUs is not an issue they're available everywhere, but how can a hobbyist get hold of a MIPS CPU, PowerPC CPU or an ARM CPU to use in a homebrew project?
Peripherals. The non-amd ones tend to have more built-in peripherals that are more suitable for an embedded device; the Athlon needs a lot of support chips. Now, AMD does make embedded CPUs (like the geode) but they're not athlons.
Digikey. Cirrus ARM9 cpu's are $13 to $27 quantity one, including LQFP and TQFP packages. Freescale PPC starts at $34 but they're all BGA.
Thanks for the fast reply! Also, I'm curious, with RISC processors costing just as much and in some cases more than a PLD (such as a FPGA or CPLD), why don't companies go with a PLD and just get the cores they require?
Some do, but most "standard" cores, like an ARM, need to be licensed at fairly high cost. Unless you are building a piece of consumer electronics that will sell in quantities of 100's of thousands, it may not be cost effective compared to a working, debugged, and documented processor.
Also consider the fact that a PLD capable of implementing and ARM5 is usually more expensive than a low cost ARM5 in the first place. Don't even begin to talk about more complex processors like the PowerPC.
Implementing off the shelf CPUs uses up lots of PLD space. The alternative, implementing special PLD friendly cut-down CPU like the Nios is more reasonable. But the tradeoff is there are fewer development tools for these cut-down CPUs are compared to mature off the shelf CPUs like the ARM or PowerPC.
So, use a custom CPU on a PLD and maybe* make your hardware developers happy or use an off the shelf CPU and definitely make your software developers happy -- that's the tradeoff. And remember, it is software that often slows down a project. Anything you do to slow down software development is not good for the project.
Note: *maybe, because it may not make the guy who has to implement the CPU happy for all the extra work he must do but it will certainly make the board-level guys happy for having less to route.
Your experience is actually the exact reverse of reality. This is to be expected because the embedded world, being embedded, runs quietly in the background without the world noticing.
VIA started out in the embedded business in the late 90s manufacturing
386 compatible CPUs for the embedded market where power and cost, not speed, is the main concern. There are a number of Taiwanese companies manufacturing x86 CPUs (one of my favourite is DM&P for the heavy peripheral integration they do -- no need chipsets if your app is small enough!). VIA just happened to grow large enough to be noticed by consumers.
Chances are the point of sale system at the local supermarket runs on VIA CPUs. Way back in 2000 I got involved in developing monitoring systems for electric substations. Those used VIA CPUs. I know companies manufacturing traffic lights using VIA CPUs as their master controller. VIA CPUs are all around you, you just don't notice them much. Their success in the embedded market is probably why they got brave enough to venture into the consumer market.
Typically embedded systems developers would buy them pre-soldered to motherboards. Even for non-x86 CPUs like the ARM or PowerPC. If you're looking for very small form factor motherboards (think credit card sized) check out Advantech.
Because they do not actually cost 'as much, and in some cases more'. If you do your maths right, you'll find Microcontrollers + peripherals + Code memory, come in cheaper than FPGA. The FPGA makes sense only in special (lower volume) cases. Such as a special combination of peripherals, or a special memory mapping of HW, or FPGA as FPU etc. It will always be cheaper to use sandard silicon, if that silicon is able to do the task.
VIA seem to be ramping their efforts in this area.
I suspect Intel are about to follow into the same power-envelope, as Intel recently sold off a chunk of their XScale business - the x86 stuff in the labs, will be more than power competitive. Looks like something of a resurgance of x86 into embedded, as for a while there, they chased the GHz at all costs, and Watts were secondary. Blade Servers, and ultra-mobile apps have pushed that along.
In general you don't see many fully custom x86-based designs because the only legitimate reason for designing in x86 is if you need to run a GP PC OS. This means you're designing a PC. There is a great deal of domain-specific knowledge in such a task, and so it's carried out by specialists.
Some years ago I ported Xfree86 to an embedded PowerPC platform. The colors and bitmap text was all wrong due to big/little-endian ordering. In theory I don't think it would have been more difficult to design a VIA based platform than than the PowerPC one, assuming VIA provide decent reference designs and support.
A: Because it messes up the order in which people normally read text.
Q: Why is top-posting such a bad thing?
Basically it's the cost. For instance I can get an ARM Cortex M3 for less than US$6. Also it's very easy (relatively) to design with embedded processors -- designing with an Athlon would lead to a very complex PCB layout.
If you're talking about one-off homebrew, then you can't go past a discarded PC motherboard. You'll even find them on the footpath when people throw them out.
If you want to use an ARM (for instance), then you'll have to go to a local distributor. The best value is to get an evaluation board but even these aren't cheap. A STM32 (Cortex M3) Evaluation Board from STMicroelectronics cost me US$250. It has:
- STM32 -- Cortex M3 core
- USB slave
- SD (MMC) card interface
- TFT Colour Graphics LCD
- Lots of I/O
- Simple keypad and joystick (lever)
- IAR Demo Compiler (limited to 32K) & IDE
- IAR J-Link JTAG Debugger
Alternatively you can order development boards from
--- I know they're in Bulgaria. But a few friends of mine have ordered their developments boards and are happy with them.
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