ADLINK aTCA-6250 - Manual (Page 80)

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Interrupt 19 is the software interrupt that handles the boot disk function. When set to
Enabled, this item allows the option ROMs to trap interrupt 19.
CSM Support
Use this item to enable or disable CSM support. For legacy OS application, CSM is
non-EFI environment for proper operation.
Boot Option Priorities
It shows the boot priority of boot devices. User can adjust the order to make
customized boot priority of found bootable devices.