30 Jun
2012
30 Jun
'12
11:56 a.m.
On 29 June 2012 23:15, Tony Duell <ard at p850ug1.demon.co.uk> wrote:
Then it would cost significantly more than =C2=A330.
True. But a prodcut I can't use is surely a total waste of money.
IMHO documentation is not an option, it's essential. If you can't work
out how to use something, it's *(by defintion) useless.
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
Origianlyl it was climed ot be 'open'. I have now relaised that this
'open' is not what I would call it.
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.
For an embeeded use, presumably you don't; need all that once it's
working...
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 thos=
e
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=CF=80 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.
Right... It is presumably powerful enough for the application I've just
suggested (given that hte origianl HP drive units used a 68B09, albeit
with supporting hardware).
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.
Is that fully docuemtned? In otehr wordsm if you don't want video
functions at all, can you work with the bare metal?
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.
THat makes little differnece practically, I do realise it's essnetially
one big 'chip' in the middle (I had heard it was actually deveral
silicon dice in the package, but that makes no practical difference either).
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 fr=
om
C (I assuem there's a C vompiler included
with the OS).
Don't know.
Wikipedia says:
Low-level peripherals: 8 =C3=97 GPIO, UART, I=C2=B2C bus, SPI bus with tw=
o 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
I wonder how much of it is easily accessible from Linux. Are there
supplied libraries to talk to I2C devies, etc?
Anyway, the problems for me now are hte lack of docuemntation, the
closed-source OS (not somethign I want on any machien I have to debug)
and the fact it appears you can't actually get one without a long wait.
-tony