On Sun, 26 May 2013 00:12:58 +0000 li...@lazygranch.com wrote: > If you go arm cortex
A little note here: Arm Cortex are multiple families of processors for different uses. And they vary a lot! Cortex-M: This family is ment to replace the old ARM7TDMI chips that are so ubiquitous. They are microcontrollers optimized for low power consumption with still a lot of peripherals and enough computation power to do things that recently needed a much larger and power hungry chip. They usually are run with the application writtend directly for the bare metal, ie without an OS. Or at most with a very thin layer of an RTOS. This family currently splits into three types of cores: Cortex-M3: this is the wast majority of todays new Arm uC chips. General purpose, does fit for most of the projects that require an uC. Cortex-M4: an upgraded version of the M3 that can run at higher clocks (i've seen up to 180MHz) and contains a single precision floating point unit. Mainly thought for projects that need a little bit more computing power or those that would benefit from floating point arithmetic. Cortex-M0: This can be seen as a shrunk down version of the M3. It is optimized for lower power applications than the M3 and meant to replace the 16bit uCs with a more versatile and easier to code for 32bit uC. Cortex-A: This family are the so called "application processors" and are the replacement for the venerable ARM9 and ARM11 families. They are supposed to run Linux, QNX or something similar, and on top of that your application. These parts start from 500MHz clock and go to 1.5GHz, from single core to quad core. So you have a damn lot of computation power. The usual use case for those is to control a user interface on an LCD with touch screen, do complex network protocols and stuff like that. Anything you wouldnt want to code yourself but a modern OS provides you for free. Big disadvantage of those cores is, that they are only available in BGA cases (i've not yet seen one available in QFP, if you are limited to that, choose from an ARM9), hence you usually want to buy a board that contains such a processor including its power supply and basic peripherals. E.g. the beaglebone black. Cortex-R: This family goes also into the category of application processors, but are optimized for real time applications. I did not have the chance to have a deeper look into them, yet. Thus i cannot say much about them. > and linux, you will need to make your code a "service." > You will want it to start up by itself and if for some reason it crashes, > you will want it to restart itself. The buzzword is "harden" and the > techniques vary depending on the distribution. The advantage of running within an OS is that you can do that easily. You don't have to rely on external components like watchdogs to catch you in case something goes wrong. Also debugging is a lot easier as you are working in user space instead of on bare metal. Unfortunately, this makes people to code more sloppy, and together with more code that is run on such systems, the application gets a lot more fragile. But if you keep writing clean code, such applications are as stable and "hard" as on microcontrollers. > > You should check the architecture of the system. I didn't realize many of > these boards run the ethernet off the usb hub. My recollection is the a10 > used by Allwinner does not do that. I think you mean the Raspberry Pi here. It's the only one i'm aware of that provides an ethernet interface on board, although it doesn't have an ethernet MAC on-chip. I especially want to point out here that the processor of the RPI was originally designed as a setop box processor. That's why it looks like a huge GPU with a tinsy CPU attached. It also explains the lack of documentation (everything is under NDA) and why the interfaces are so quirky. For most projects, i would advise against the use of the RPI unless you are building something that relies heavily on a GPU and needs little else. There are other, better boards to choose from that are in the same price range or even cheaper. Examples are the aformentioned beaglebone black (using an Ti AM3359), or the two olixino boards (one featuring a Freescale i.MX23 and the other an AllWinner A10). Attila Kinali -- The people on 4chan are like brilliant psychologists who also happen to be insane and gross. -- unknown _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.