6.6 Dependencies

The Boot ROM uses the user-configured boot settings defined in the Boot Configuration (BOOTCFG) fuses. No external hardware connections are required for Boot ROM operation, provided the device operates within the Electrical Specifications.

Note: Users must ensure that the pin selected for configuring the BOOTCFG.BOOT_GPIOSEL fuse is configured in a way that does not interfere with the overall hardware functionality of the application. Refer also to the BOOTCFG - Boot Configuration Fuses chapter.

Clocks

When the Boot ROM transitions the device to the first mutable application executable, the clock system is configured to use OSCHF at 4 MHz as the source for GCLK0 and, consequently, MCLK. This ensures consistent and deterministic behavior after the boot phase. Any clock configuration changes are performed by the user application after control is transferred from the Boot ROM.

Configuration Flash Memory (CFM)

The Boot ROM reads the Boot Configuration (BOOTCFG) fuses and writes their configuration information, such as Boot Loader Size or Watchdog Timer parameters, to the respective peripheral registers. These user-defined fuse values must be correctly programmed using the supported device programmer to ensure proper device operation. Refer to the BOOTCFG - Boot Configuration Fuses section for additional information.

Note: Incorrect fuse settings may prevent the device from booting successfully. In extreme cases, invalid fuse configurations may render the device permanently non-functional.

Memories

The Boot ROM may use the SRAM during start-up. Before transferring control to the user application, all locations of the SRAM are written to 0x0000. Do not rely on any pre-initialized data in this region when developing the first mutable application code.

Debug Operation

The device supports both hot-plugging and cold-plugging. The interaction between the external debugger and the device is controlled by the Debugger Access Level (DAL0 or DAL2). See the Functional Description for more details.