29 Jun
2012
29 Jun
'12
6:44 p.m.
On 29 June 2012 23:15, Tony Duell <ard at p850ug1.demon.co.uk> wrote:
Then it would cost significantly more than ?30.
But if that is what you wanted, then there are such devices out there:
various small Android-powered all-in-one ARM machines for under ?100.
Tony *might*
approve if the published documentation included detailed
instructions on how to mine your own copper ore, smelt it, build a
silicon refinery, fabricate your own CPU, spin glass fibre and
synthesize resin and then manufacture your own circuit board.
But I do emphasize the "might" here...
Actually, I'd be very likely to approve of it if :
It came complete, that is to say I could just plug it in and go without
having to pay to download and print manuals, download the OS, etc The docuemtnation let me figure out how to use the
thing.
It's a device to teach kids programming. The bulk of the information
is on the web. You'd need a Web-capable computer and a broadband
connection.
Given that, I might actualyl buy one.
It is really not a device for you, given your predilection for
vintage, technically-documented hardware. It's a closed-spec
undocumented system-on-a-chip with some supporting hardware, which
assumes that the owner has a basic set of 21st century equipment to
hand: USB hub, USB keyboard, USB mouse, USB power supply, SD media and
a host PC that can read/write SD media, an HDMI-capable
high-definition flatscreen TV and so on. None of which you own and
from what you have told me before none of which you
want to own.
A couple of serious questions :
1) AS has been confiremd the data sheet on the main 'chip' doesn't
include docuemtnation on certain parts of it (video-related?). Are those
parts simply not used by the standard linux for the Rpi, or are the
drives supplied as binary-only, or what?
Binary drivers for Linux only, no other OS. GPU is proprietary,
undocumented and protected Broadcom IP; they will not disclose
details. Even the Linux driver only exposes certain, limited APIs and
functions that the R? Foundation have paid for, such as H.264 video
decode. There are lots of other functions in the GPU that Linux cannot
access and never will unless someone pays quite a lot of license fees
to Broadcom.
The device /has/ no discrete CPU; the processor is a small, low-spec,
old-fashioned ARM core of a type long superseded and no longer
supported by most current Linux distributions, which has been masked
onto some spare gates on one corner of the GPU die.
The machine boots because the GPU reads a FAT filesystem on the SD
card, looks for files of certain names, loads them into RAM and then
boots the ARM core and starts it executing.
It's not a CPU with an attached GPU as most modern computers; it's a
GPU with an afterthought of a CPU bolted onto the side.
2) I understnad the's some kind of GPIO/user port.
How many lines, are
they individually selectable for direction? Can this be easilly used from
C (I assuem there's a C vompiler included with the OS).
Don't know.
Wikipedia says:
Low-level peripherals: 8 ? GPIO, UART, I?C bus, SPI bus with two chip
selects, +3.3 V, +5 V, ground
... If that means anything to you; it doesn't to me mostly.
It's accessible from Linux and therefore from any Linux programming
language, in principle. Distros available include a very elderly
version of Ubuntu, a more current Debian that can't use the FPU, a
work-in-progress Debian remix compiled for the
elderly-ARM-core-plus-hardware-floating-point called Raspbian (which
will be the one of choice once it's finished), and a not-all-there
Fedora.
It also runs Acorn RISC OS, in the Risc OS Open Ltd variant - but the
port is very new and experimental and unstable.
--
Liam Proven ? Profile: http://lproven.livejournal.com/profile
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