Raspberry Pi - Hardware Flaws and Fixups?

Now that people have actually started receiving the boards so the design in final, is the schematic close to being posted?  I looked around again in various likely places just now, but haven't spotted it yet.

actually, the design may not be quite final yet.  Liz said: "Happily, we’ve found it doesn’t need a shielded enclosure to reach Class B, although it will require a (very minimal) redesign." http://www.raspberrypi.org/archives/978, page 3, April 10, 2012 at 7:04 pm.

It hasn't been announced when such a change might be implemented, but probably better sooner rather than later, given the large production runs planned, perhaps along with a change to fix the SD card voltage issue.

cookiemonster,

  It's a bit confusing because there are 2 separate changes needed.

The software (gpu blob) change for the HDMI that you mention was needed

for Class A certification.   A completely separate hardware redesign change

was found to be needed for Class B certification as Liz described in the

linked forum.   Since there obviously wasn't time to make the hardware change,

only Class A certification was obtained.

We haven't been told exactly what the hardware change involves, or when it

will be implemented.  Maybe PeteL can enlighten us soon.

cookiemonster,

  There are a variety of reasons for wanting to see a schematic besides wanting

to modify a board.  For example, a schematic might be useful for explaining what

modification is needed for the Class B issue Liz mentioned above, or for explaining

what modifications might be needed to get I2S functionality back..

I'm the proud owner of a 'pi.

Broadcom has released the "Arm peripherals" datasheet of the BCM2835 chip. First things first, I wanted to see something from the UART. So I search the data sheet for UART and find that there are three uarts, two different designs. The pins connected to the GPIO are labeled: "UART RX" and "UART TX" not "UART 2 TX". Which one is it?

Turns out I was able to figure it out without crashing my 'pi. Good!

However next in line is my I2C interface. This too is labeled on the GPIO port as: I2C SDA, I2C SCL, and I'll have to guess which of the several I2C interfaces is connected to the GPIO pins and that by attempting to send a byte there I don't crash or break things if I happen to pick the wrong one....

These are things that a schematic tells you.

Similarly, a schematic can answer questions like:

• If I want to power my 'PI, can I do so from the 5V pin on the GPIO port?
• What will happen if I want to save power and directly provide 3.3V on the GPIO port? (*)
• In that case, should I leave teh 5V floating, short it to 3.3V, or provide a diode between 3.3V and 5V?

Those are just the questions that I have come across on my first day of owning a raspberry pi that a schematic would have answered.

(*) eventually I might install a RPI in my car. Maybe it will stay on 24/7. In that case saving power is important, to prevent draining the starter battery. A 12V->3.3V switching powersupply will do better than a 12V->5V switcher and then letting the linear converter on the board do the 3.3V conversion.

PeteL, are you still reading this thread?

You mentioned using a high quality micro USB connector with through-hole pins.

It seems the chinese were able to substitute a cheaper component for the microUSB. I don't seen any through-holes on the connector. (the holes are there on the board, but there is no metal sticking through the board!)

Roger & all

I am - but just got home after a 12 hr flight (family holiday).  Will start to respond to all the issues (including Pins and Schematics) as soon as I'm awake enough to make sensible comments. We are working on mods and I would like to make sure that on any released schematics you have an idea what is vunerable to change.

Sorry for the blackout - did post on my e14 status but I don't think it is really visible!

Cheers

Pete

Thanks Pete.  But don't bother improving the schematic further before initial release.  The board is already in the hands of customers, so whatever you managed to work from, that'll be good enough as a starting point for those who need it.  Release it as is, as version 1.0.  Subsequent v1.1 etc releases can carry the improvements.

"Release early, release often" applies as much to schematics as it does to open source software.  Others will help you improve it, both with suggestions and with actual updates if you're using some standard schematic tool.

Morgaine.

Pete: great to hear you are back from a well-earned vacation! Hope to hear more soon once you've rested up from the trip. 

I think as long as the date and the version are clearly marked on the schematic, that's all you should need to do for now.  A "wish list" for the next board spin is fine, but not as high a priority for those of us on the outside just now, in my opinion.

As you'll see from the RasPi forums, seems like a lot of issues which may be related to cheap USB cables having high resistance (would you believe up to 4 ohms? that would drop your 5V down to 3V, at 500 mA). Also a lot of SD card questions which in some cases have been pilot error (incorrect use of 'dd' utility) and sometimes apparently incompatible cards. And if the below claim is true, it certainly doesn't help finding a reliable card:

http://www.petapixel.com/2011/05/20/one-third-of-the-sandisk-memory-cards-on-earth-are-counterfeit/

Hi  All

Schematics - Yes we have had a discussion on this and there are a set in the release pipe and they reflect the current status of the delivered boards as of today.  Will post back here as soon as they are ready for download on the raspberrypi main site ( I know Liz and Eben are still running round like mad things).

The Pi board has a set of 4 hard links that can be read by the firmware so it knows which version of the board it has and can configure accordingly.  However, anyone who is doing something more than just software needs to know what may change (e.g. GPIO) so they can plan for it. We have a candidate list and this will be published soon but now separately from schematics.

Bright LEDs - They are, we will look at dimming them down but some people who are designing cases want to use light pipes of some sort and this makes them harder to see if they are not 'bright'.  Guess we could save some power?

Cables - we have not seen a problem with any of the ones we have been using - or reports from developers, BUT now we have a population of more than a few hundred I can see issues like this appearing.  We just need to work together to pass around knowledge.

More later - need to dash.

Pete

Roger,

  That's an interesting observation that the micro USB connector may have been

substituted for a cheaper surface-mount one.  Paul Maunders, with beta board #8,

commented on how rugged the power connector felt:

but GizmoB73, with a production road-test unit commented just the opposite.

Now that apparent conflict makes sense.

After the ethernet jack issue, it makes you wonder if any other substitutions were made.

FYI, I've powercycled my RPI about 100 times yesterday, but I always use the connector on the other side of the power cable. This way my RPI doesn't wear down, and I can start over with a new $3 USB-power-cable after the second insertion on the RPI....

FYI, I've powercycled my RPI about 100 times yesterday, but I always use the connector on the other side of the power cable. This way my RPI doesn't wear down, and I can start over with a new $3 USB-power-cable after the second insertion on the RPI....

I power cycle mine a lot too, and I really wouldn't want to put all that strain on the Pi's power connector either.  I always disconnect the power further down the line.

Pete, I guess the schematics would tell me this, but do you know if the Pi supports the type of high current connections that Ipod/Ipad do?  i.e. a resistive connection to the D+ and D- pins?  If so, there might not be so much of a voltage drop if we have current going through all four wire (albeit smaller on the D- and D+ wires).

Gizmo,

Those voltages on D+ and D- are not power-carrying.
Apple wanted to make a powersupply that provided 1A of charging current, but didn't want to be breaking any 500mA standard-USB power-sources. So they decided that 2.0V on D+ and 2.7V on D- will indicate that this is a 1A capable apple charger.

This is an easy and cheap way to identify the charger. It's just identification.

The D+ and D- lines on the Micro USB connector are not connected to anything on the RPI.

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Pete, Not sure if you've heard about this, but some people are a bit disappointed that I2S has been dropped. So those are planning on using those strapped pins as access points for the I2S hardware on the SOC.

If another "board revision" possibility presents itself, that might lead to less problems for those people.

I was thinking about: The GPU already knows its serial number/MAC address. So could that be used? You guys have 1M mac addresses, right? So if you reserve the top two bits for board revision, you're leaving some 150k mac addresses unused if the current "batch" of 100k boards are rev 0, and the next will be rev 1.

Or if that sounds wasteful, the mechanism for "personalizing" the SOC that is used for the MAC address can also be used for passing BOARDREV=XXX on the kernel commandline.

On the other hand, that would require a ROM firmware upgrade to the SOC, right? Is that really ROM? Flash? OTP?