C62 and C67 are too large and cause too-slow crystal start to use system bootloader in DFU mode

[zbrozek]

The onboard system bootloader (BOOT0 set high, BOOT1 set low) present on the STM3240xxx series only waits 780 microseconds for the crystal to start. The SKR Pro 1.1 comes with 22 pF capacitors that over-load the crystal such that it can't start quickly enough to enable USB support within the system bootloader.

I replaced these capacitors with 12 pF capacitors and now the startup is fast enough that the SKR Pro 1.1 is able to enumerate as a USB DFU device.

[mqt0029]

Can someone @bigtreetech verify this is an issue with USB enumeration? Is this why my SKR Pro V1.1 USB-A USB-B port to OctoPi or Pronterface never worked (USB Descriptor Request Failed) no matter what I tried?

[zbrozek]

@mqt0029 This is only relevant if you're trying to use the DFU bootloader, which is unlikely if you're thinking about OctoPi. Also presumably you meant the USB-B connector?

[mqt0029]

Apologies was typing it up halfway through trying to get OctoPi to work with this board. And yes I meant the USB-B connector. So far trying all the firmware flashes which claims to have bootloader or USB serial does nothing:

• 115 .bin reads all F in ST-Link Util

• 72 brings it back to where it all started

• scrambling 1, -1, and 6 in latest Marlin, latest bugfix, and BTT Demo for SERIAL_PORT only works with ESP-01 and TFT 35 V2.0, USB Virtual COM never came up and error out in Windows. (from various issues on both Marlin and BTT repos)

Sorry for the wall of text. It is a long shot, but at this point I'm beginning to suspect everything possible, including bad USB setup from within the bootloader.