Hi all,
I have designed my own PCB with LPC11U68. Here is the schematic:
We cannot read well but the capacitors attached to the crystal are 18pF and the crystal is this one: http://www.digikey.com/product-detail/en/7M-12.000MEEQ-T/887-1316-1-ND/2207898
The ISP is expected to be through USB (I cannot change to UART). I have a 12Mhz external crystal.
When I plug the board to USB, I can see the USB be enumerated by Linux:
[46830.963165] scsi79 : usb-storage 2-1.3:1.0
[46831.436294] usb 2-1.3: USB disconnect, device number 68
[46831.634474] usb 2-1.3: new full-speed USB device number 69 using ehci-pci
[46831.729533] usb 2-1.3: New USB device found, idVendor=1fc9, idProduct=0017
[46831.729542] usb 2-1.3: New USB device strings: Mfr=1, Product=2, SerialNumber=3
[46831.729548] usb 2-1.3: Product: LPC1XXX IFLASH
[46831.729553] usb 2-1.3: Manufacturer: NXP
[46831.729557] usb 2-1.3: SerialNumber: ISP
[46831.730339] usb-storage 2-1.3:1.0: USB Mass Storage device detected
But I could only access the USB mass-storage the first time I plugged it. But I did not have time to do anything else, after few seconds the mass-storage disappeared and since then every time I plug the device it constantly enumerated but without mounting the mass-storage; even after leaving the device unplugged for an hour.
The only one time the LPC was successful mounted I had this output:
[234963.388167] usb 1-1.1: new full-speed USB device number 113 using ehci-pci
[234963.483203] usb 1-1.1: New USB device found, idVendor=1fc9, idProduct=0017
[234963.483210] usb 1-1.1: New USB device strings: Mfr=1, Product=2, SerialNumber=3
[234963.483215] usb 1-1.1: Product: LPC1XXX IFLASH
[234963.483218] usb 1-1.1: Manufacturer: NXP
[234963.483222] usb 1-1.1: SerialNumber: ISP
[234963.483994] usb-storage 1-1.1:1.0: USB Mass Storage device detected
[234963.484215] scsi122 : usb-storage 1-1.1:1.0
mtp-probe: checking bus 1, device 113: "/sys/devices/pci0000:00/0000:00:1a.0/usb1/1-1/1-1.1"
mtp-probe: bus: 1, device: 113 was not an MTP device
[234964.485934] scsi 122:0:0:0: Direct-Access NXP LPC1XXX IFLASH 1.0 PQ: 0 ANSI: 0 CCS
[234964.486568] sd 122:0:0:0: Attached scsi generic sg2 type 0
[234964.487081] sd 122:0:0:0: [sdb] 516 512-byte logical blocks: (264 kB/258 KiB)
[234964.488418] sd 122:0:0:0: [sdb] Write Protect is off
[234964.488427] sd 122:0:0:0: [sdb] Mode Sense: 03 00 00 00
[234964.492817] sd 122:0:0:0: [sdb] No Caching mode page found
[234964.492827] sd 122:0:0:0: [sdb] Assuming drive cache: write through
[234964.497456] sd 122:0:0:0: [sdb] No Caching mode page found
[234964.497465] sd 122:0:0:0: [sdb] Assuming drive cache: write through
[234964.506426] sdb:
[234964.511600] sd 122:0:0:0: [sdb] No Caching mode page found
[234964.511607] sd 122:0:0:0: [sdb] Assuming drive cache: write through
[234964.511613] sd 122:0:0:0: [sdb] Attached SCSI removable disk
udisksd[2678]: Mounted /dev/sdb at /media/olivier/CRP DISABLD on behalf of uid 1000
I tried on a different computer and it also continuously enumerated without mounting the mass-storage.
I can briefly do a `lsusb` and Linux seems to return the appropriate info:
Device Descriptor:
bLength 18
bDescriptorType 1
bcdUSB 2.00
bDeviceClass 0 (Defined at Interface level)
bDeviceSubClass 0
bDeviceProtocol 0
bMaxPacketSize0 64
idVendor 0x1fc9 NXP Semiconductors
idProduct 0x0017
bcdDevice d.01
iManufacturer 1
iProduct 2
iSerial 3
bNumConfigurations 1
Configuration Descriptor:
bLength 9
bDescriptorType 2
wTotalLength 32
bNumInterfaces 1
bConfigurationValue 1
iConfiguration 0
bmAttributes 0xc0
Self Powered
MaxPower 100mA
Interface Descriptor:
bLength 9
bDescriptorType 4
bInterfaceNumber 0
bAlternateSetting 0
bNumEndpoints 2
bInterfaceClass 8 Mass Storage
bInterfaceSubClass 6 SCSI
bInterfaceProtocol 80 Bulk-Only
iInterface 4
Endpoint Descriptor:
bLength 7
bDescriptorType 5
bEndpointAddress 0x81 EP 1 IN
bmAttributes 2
Transfer Type Bulk
Synch Type None
Usage Type Data
wMaxPacketSize 0x0040 1x 64 bytes
bInterval 0
Endpoint Descriptor:
bLength 7
bDescriptorType 5
bEndpointAddress 0x01 EP 1 OUT
bmAttributes 2
Transfer Type Bulk
Synch Type None
Usage Type Data
wMaxPacketSize 0x0040 1x 64 bytes
bInterval 0
I am trying to think about potential issues:
- Software: Unlikely as it is still in the NXP ROM Bootloader
- Design: Possible, I discovered after sending my design to the PCB manufacturer that NXP has added many more capacitors on the voltage lines: https://www.lpcware.com/system/files/LPC11U68_Xpresso_v2_Schematic_RevC_1.pdf .
- Soldering: Why not (I am not necessary an expert in SMD soldering) but it would not explain why it "almost" work
With a logic analyzer, the crystal signals XTALIN and XTALOUT look like that: 
I confirm XTALOUT has a frequency of 12MHz.
The USB signals look like that (I removed the crystal signals):
I compare both last packets before the interruption of the USB signals and they are different.
