samd21_usbcdc_reboot

Summary

USB-CDC command initiated reboot to bootloader with an Atmel SAMD21G18. ArduinoCore-samd also implements this in its own way, but this is useful if you don't want to use Arduino libraries (e.g. for a custom board). Also implements some other necesities such as a printf_cdc and simple console that processes newline terminated commands.

ASF Project

samd21_usbcdc_reboot is a bare-bones AtmelStudio ASF project for the SAMD21G18 with the following modifications and additions:

• USB callbacks for checking for DTR/1200bps
• Custom reset function starts at flash segment 0x2000 (see Bootloader section below)
• A redirected printf_cdc for virtual serial port io

Configuration

All of this config is in the project in the repo. If you're doing this from scratch as an ASF project, you can use the notes below

• Add .text=0x2000 to the FLASH segment in the linker script (Linker config in Atmel Studio or your Makefile)
• Set up the 48Mhz GCLK needed for USB (hpl_gclk_config.h or the via the image below)

Snapshots of the ASF config if you prefer to set it up that way:

Bootloader

I utilized the ArduinoCore-samd bootloader for the MK-Zero (SAMD21) board. You'll need to make some small changes in the Makefile if going this route:

• add CRYSTALLESS to the extra definitions.
  • example: CFLAGS_EXTRA=-D__SAMD21G18A__ -DBOARD_ID_$(BOARD_ID) -D$(SAM_BA_INTERFACES) -DCRYSTALLESS
• change SAM_BA_INTERFACES to SAM_BA_USBCDC_ONLY
  • example: SAM_BA_INTERFACES?=SAM_BA_USBCDC_ONLY

Remember to change the flash segment app start address in the previous project, especially if using a smaller bootloader.

VID/PID/String description

By default your virtual serial port will enumerate with a text summary like ATMEL_CDC_ASF_EXAMPLE. If you want to change the text summary to something else, check the strings definitions in usb/class/cdc/device/atmel_devices_cdc.inf.