XHRA-2HPA and usb enumeration

Technical questions regarding the XTC tools and programming with XMOS.
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mon2
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Post by mon2 »

Hi virtex.

1) R802 is the wrong value as shown in the schematic.The value should be 43R2 = 43.2 ohms 1%. Schematic is showing 43k2 = 43.2k. Suspecting this to be the root cause of your USB enumeration issues.

Image

2) Be sure to protect VBUS against in rush current damage which a number of developers have reported. Respectively, XMOS has now documented a small filter circuit to prevent such future issues. However, we believe a more elegant solution is to place one of the many USB load switches which offer this same feature along with many others. Hoping there is some ESD transient protection on the USB interface. USB isolation will be a bonus.

3) Do not leave pin 1 on the CMOS oscillator to always drive your clock oscillator. While this should hold true, we dealt with the mfr that supplies FOX in Asia and did get stung with a QC issue where we "assumed" pin 1 can be left open since internally, there is a pull-up. Well this failed on 2-3 boards out of thousands we assembled. Summary, it was a pain to resolve so best to add a trace onto pin 1 of your SMD oscillator to 3v3 to be 110% sure of this ENABLE.

4) Be sure your firmware is correct. Compare against our dumps posted here:

https://axxonshare.s3.amazonaws.com/xmo ... backup.zip

During our review, we programmed the QSPI flash target using standard SPI commands (took forever) using StartKit. At the end of the painful 7-10 minutes of SPI programming, then enabled the QPSI bit and soldered back onto the XMOS ref design. Worked fine. Hope this helps.


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