USBHid | Handle multiple USB HID compatible devices in C | Change Data Capture library

Yes, you are looking for the -P flag, it needs the path to the serial device of the AVR when it's in its bootloader. As long as it is a normal itsybitsy, and not one that's been modified to work without the bootloader, you need to get it into the bootloader by hitting the reset button twice withing 750ms, and within 8 seconds you need to run the avrdude command.

For the -P flag, you posted your dmesg output, and it's the same as my machine, /dev/ttyACM0.

So, my dance to get mine is to hold reset for a count of 5 (to let Linux notice it's gone and free the device it was assigned), hit the reset button again quickly, wait for a second (but not too long; Linux needs to reallocate the tty but you cannot miss the bootloader window), then run the avrdude command:

So it turns out there is a short somewhere between the RX pin and the +3.3V pin which is not allowing me to send anything to the board. Thank you to those who have commented.

There's 2 questions here:

a) How to execute INVD (unsafely)

For this, you need to be running at CPL=0, and you have to make sure the CPU isn't using any "processor reserved memory protections" which are part of Intel's Software Guard Extensions (an extension to allow programs to have a shielded/private/encrypted space that the OS can't tamper with, often used for digital rights management schemes but possibly usable for enhancing security/confidentiality of other things).

Note that SGX is supported in recent versions of Linux, but I'm not sure when support was introduced or how old your kernel is, or if it's enabled/disabled.

If either of these isn't true (e.g. you're at CPL=3 or there are "processor reserved memory protections) you will get a general protection fault exception.

b) How to execute INVD Safely

For this, you have to make sure that the caches (which includes "external caches" - e.g. possibly including things like eDRAM and caches built into non-volatile RAM) don't contain any modified data that will cause problems if lost. This includes data from:

• IRQs. These can be disabled.

• NMI and machine check exceptions. For a running OS it's mostly impossible to stop/disable these and if you can disable them then it's like crossing your fingers while ignoring critical hardware failures (an extremely bad idea).

• the firmware's System Management Mode. This is a special CPU mode the firmware uses for various things (e.g. ECC scrubbing, some power management, emulation of legacy devices) that't beyond the control of the OS/kernel. It can't be disabled.

• writes done by the CPU itself. This includes updating the accessed/dirty flags in page tables (which can not be disabled), plus any performance monitoring or debugging features that store data in memory (which can be "not enabled").

With these restrictions (and not forgetting the performance problems) there are only 2 cases where INVD might be sane - early firmware code that needs to determine RAM chip sizes and configure memory controllers (where it's very likely to be useful/sane), and the instant before the computer is turned off (where it's likely to be pointless).

Guesswork

I'm guessing (based on my inability to think of any other plausible reason) that you want to construct temporary shielded/private area of memory (to enhance security - e.g. so that the data you put in that area won't/can't leak into RAM). In this case (ironically) it's possible that the tool designed specifically for this job (SGX) is preventing you from doing it badly.

It was variable scope, and it's because the PROPERTY_ENTRY_REF() macro does define a new variable:

It looks like the problem was introduced by the patch: regulator: stpmic1: Usb boost over-current protection workaround.

• The "boost" interrupt handler stpmic1_boost_irq_handler calls regulator_lock(usb_data->boost_rdev);
• The "boost" interrupt handler (stpmic1_boost_irq_handler) is set up by the stpmic1_boost_register function, but usb_data->boost_rdev is still null at this time.
• usb_data->boost_rdev is set to the return value of the stpmic1_boost_register function by thestpmic1_regulator_probe function.
• If the "boost" interrupt handler stpmic1_boost_irq_handler gets called before usb_data->boost_rdev has been set by the stpmic1_regulator_probe function, then the crash occurs.

A workaround would be to set usb_data->boost_rdev = rdev; in the stpmic1_boost_register function after it has set rdev but before it sets up the interrupt handler.

This should be reported to the author of the patch. See the "Signed-off-by:" line in the patch for the email address.

It turns out OHCI driver is needed to handle low speed peripherals even if they're connected to USB2 (EHCI) controller.

Actually MT7628 has a "secondary" OHCI controller not even advertised in Data Sheet.

This means that, on top of selecting CONFIG_USB_OHCI_HCD=m and CONFIG_USB_OHCI_HCD_PLATFORM=m also the following patch is needed:

In the meantime I did some testings and find out, that we already need a Kernel driver for this ethernet card:

As you can see in the dmesg output:

[ 5.379690] usb 1-1: New USB device found, idVendor=10c4, idProduct=ea60

Looking that up, e.g. here: https://www.google.com/search?q=usb%20vendor%20id%2010c4

Tells you that it's a "Silicon Labs" USB device, who also make the CP2102.

The log does not identify other devices (ignore the linux kernel root hub). So either you have also a CP2102 attached (and the FTDI is not properly connected) or the device you think is a FTDI based device, is not.

In addition you can identify currently enumerated devices using the lsusb command.

The automatic loading is usually done by udev or a similar user space daemon/mechanism. A decent explanation can be found e.g. here: https://lwn.net/Articles/740455/

Thanks to the comments. I have added copy_from_user and copy_to_user.

Now it works.