On Sun, Nov 10, 2013 at 8:16 PM, joem joem@martindale-electric.co.uk wrote:
Hmmmppp...... The is another outstanding issue that needs resolving before the next batch goes into production - this time to do with the RS232 RX line. When connected, the entire board is able to power up through the RX line. The cubieboard1,2 and iteaduino plus and EOMA-A20 boards all have same defect because I assume all of them were designed and tested by the same engineering team from Wits with no peer review input onto the process.
| ... well, the schematics for the EVB and also the schematics for the |GPL-licensed EOMA68-A10/20 CPU Card have been publicly available for |nearly two years. unfortunately we've not had you around until |recently joe... *rueful*...
If you are doing another batch, make sure the CPU board RX line doesn't power up the entire board through that line.
| not going to happen, for exactly the same reason that the RGB/TTL |lines are not going to be modified: it's too late. the PCB design |went out to the factory over two months ago when the first 30 samples |were made, and the gerbers cannot now be changed. a) it would make |the factories nervous (no way we're doing that) b) someone needs to
Don't believe in such things. Most good factories are only too glad to help down to the wire. I've changed stuff after 1st day of production.
joe you're not listening. the scale of the production facilities we're dealing with is enormous. at their *current* capacity our client is capable of making *TWENTY MILLION* CPU Cards PER WEEK. there is flat-out absolutely zero chance that we will be telling them "sorry we made a mistake, we have to change what we're delivering". our reputation would be immediately destroyed.
| so - no. no changes to the CPU Card.
If its gone to production, it not end of world.
joe - you're not listening. this is the first CPU Card. it's a MODULAR system. it's too late. there will be no changes.
if however this was a single-board system you would be absolutely right. it would be perfectly reasonable to just go and redesign the next release of the PCB.
... but this isn't a single-board system, is it?
Just more revisions are due next batch. The revision to fix RX line problem will likely be transparent to end user.
no it will not. think it through. there's due to be a batch of 2500 CPU Cards followed by another batch of 10k. these two batches are the ones that cannot be modified.
what then happens if any one of those 12500 CPU Cards is plugged into an I/O board that doesn't have the RX line-protection?
the venn diagram is as follows:
cpu card Rx-fixed IO board Rx-fixed combination OK n n N y n Y n y Y y y Y
can you see, using karnaugh mapping, that "fixing the CPU Card" is completely and totally irrelevant? the CPU Cards *have* to go out without UART-RX being fixed [for reasons already stated]. the I/O Boards therefore *have* to go out with UART-RX hardware fixes.
therefore "fixing the CPU Card" *afterwards* is not only completely irrelevant but is also *dangerous* because it will give I/O board developers the false impression that they do not need to take care of the problem.
and if that ever happens they're f*****d.
so it has to be the way that i've said it has to be, for the reasons that i've already stated that it has to be. i've looked at all the options: this is the only option. therefore we go with it.
Learn from this - always make in batches of 10 to iron out problems.
the circumstances are different. 30 samples or 10 samples, it doesn't make any difference: one of those went to our client. due to the number of fuck-ups that have already occurred (from using Wits Tech) there was absolutely no way unless it was yet another serious fuckup that we could say "i'm sorry, we have to make some minor changes".
if we did not have such large clients, or if we did not have a modular system, matters would be entirely different.
so - there's a solution: that's what we go with for the next 10 years. end of story.
l.