Custom LPC11U35 dev board - Device Descriptor Request failed w/ MSC bootloader

[lpcware]

Content originally posted in LPCWare by twiddle on Sat Feb 28 16:20:26 MST 2015
So I've put together a simple dev board intended for USB use and modelled after the schematics in the datasheet as well as the "ARM Pro Mini" project.
However, I don't appear to be getting any response out of the chip, when I connect the device to USB.
I get "Device Descriptor Request failed" from my Win8 machine, which I suspect is due to the fact, as per the datasheet's suggestion for a bus powered device, I've connected a pullup directly between USB_DP and 3V3 directly rather than using USB_CONNECT, so my computer is seeing an attached device regardless of whether the chip is actually initializing properly. USBView shows nothing being received for the device descriptor at all, which leads me to think that my chip is not functional at all.
Bearing this in mind I am posting my schematic/layout in case I've got some rudimentary error in my design, in the hopes I can get some insight into what I'm doing wrong.
Any input would be appreciated! Thanks.

Here's the layout (schematic attached below as PDF):
[img]http://i.imgur.com/ZhXxIdn.png[/img]

[lpcware]

Content originally posted in LPCWare by twiddle on Sun Mar 01 16:58:37 MST 2015
I *did* manually route this layout, to be honest, so I will compare with the autorouter output.
Maybe it's time to get off my butt and learn KiCad or something.

[lpcware]

Content originally posted in LPCWare by R2D2 on Sun Mar 01 16:56:13 MST 2015
Schematic and layout are not consistent  :O   :quest:   J)

Time to change the CAD   :)

[lpcware]

Content originally posted in LPCWare by twiddle on Sun Mar 01 16:31:31 MST 2015

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Quote: R2D2

'LPC11U35 board' and of course, 'LPC11U36 board', 'LPC11U37 board'...

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Ah... I was overcomplicating this, looking for 'minimal LPC11U3 circuit' etc etc. Kinda kicking myself, that's sorta obvious.

Talking of obvious, if you  have a look at the layout above, you'll see R1, R2, and R8 are in series rather than parallel. This essentially turns them into a voltage divider, so the MCU is only getting 1/3 of my 3V3 regulated output voltage, because my routing happens to direct 3v3 through VBUS (after R8) and then through to the other pins. So that's the first thing I will have to address. Your checklist was rather handy for reminding me to check :)

[lpcware]

Content originally posted in LPCWare by R2D2 on Sun Mar 01 07:08:27 MST 2015

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Quote: twiddle
In the interests of improving my google-fu, what query did you use to find that? I am wondering if half my problem is using the wrong search queries..

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'LPC11U35 board' and of course, 'LPC11U36 board', 'LPC11U37 board'...

So you'll find a lot of similar boards like:

http://www.blackramelectronics.com/products/dev/DEV0004/DEV0004.php

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Quote: twiddle

Is there a specific checklist that you're referring to?

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Of course my own  :D

As part of initial startup, it's of course necessary to check all MCU pins. This NXP MCU isn't very difficult to connect, so after measuring correct supply voltages it's time to flash it.

So my next checklist step is to test SWD. Since MCU is empty and therefore booting into ISP this should work without problems.
If so, the basic things are working.

Next step: a test program with crystal.

If SWD isn't working, UART bootloader is the next option. Just connecting a working UART-USB converter and FlashMagic can flash the MCU. If FlashMagic isn't working, there's usually a hardware problem...

It's useful to practise this things with a working board before, so buying a simple (LPCXpresso) board before drawing own boards usually pays off  :) 

(And no, I'm not selling LPCXpresso boards. I'm not paid for advertisement and NXP isn't paying me to write (or not write) stuff here  :O )

[lpcware]

Content originally posted in LPCWare by twiddle on Sun Mar 01 05:17:57 MST 2015

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Quote: R2D2

Google is your friend  :)

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In the interests of improving my google-fu, what query did you use to find that? I am wondering if half my problem is using the wrong search queries..

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Quote: R2D2

So you've no idea if your hardware is working at all?

Then it's time to process your hardware checklist

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As I mentioned in the OP, I made the mistake of omitting the transistor on USB_CONNECT (that is to say, the pullup on USB_DP is connected directly), which means that the device will always appear to connect to the computer regardless of whether the MCU is functional. This, quite evidently, makes it difficult to see if the MCU is functioning (I don't currently have a scope).
I've gone through with a multimeter and checked my board for shorts, and checked that all the parts seem to be functioning correctly (in that they give me the correct resistances, etc).

Is there a specific checklist that you're referring to? I've seen some manufacturers provide general PCB checklists, for example, or is this something I derive myself from my specific board implementation?

[lpcware]

Content originally posted in LPCWare by R2D2 on Sun Mar 01 04:14:48 MST 2015

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Quote: twiddle
However, looking at it it's a little difficult to ascertain what's essential for a relatively minimalist implementation such as mine...

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:quest:

Google is your friend  :)

http://shop.ngxtechnologies.com/download/Schematics/BBLPC11UXX/BB_LPC11U37_schematic.pdf

Now you should be able to see what's useful to implement and what's additional protection  :O

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Quote: twiddle
...what's actually causing my layout to not function.

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So you've no idea if your hardware is working at all?

Then it's time to process your hardware checklist  ;-)

[lpcware]

Content originally posted in LPCWare by twiddle on Sat Feb 28 21:38:53 MST 2015
Thanks for the link to that particular dev board.
However, looking at it it's a little difficult to ascertain what's essential for a relatively minimalist implementation such as mine - for example, that design contains a PRTR5V0U2X protection diode, as well as a reset supervisor. I don't recall the datasheet mentioning either of these as requirements for successful operation, though of course they should probably be present in a commercial device.
I could simply copy the circuit from that board, of course, but in order to further my own learning I'd really like to try to determine what's actually causing my layout to not function.

[lpcware]

Content originally posted in LPCWare by R2D2 on Sat Feb 28 16:43:50 MST 2015

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Quote: twiddle
Any input would be appreciated!

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http://www.embeddedartists.com/sites/default/files/support/qsb/lpc11u35/LPC11U35_QSB_rev_PA1.pdf