On ATs, INT 0aH is a hardware-generated interrupt (IRQ 2) forced by any
occurrence of IRQ 7 through IRQ 15.  These are cascaded into the secondary
interrupt controller.

The actual handler for IRQ 2 is IRQ 9, handled by INT 71H.  Normally, no
device uses IRQ 2, but an EGA or VGA may be programmed to use it to
interrupt at the start of vertical retrace (see EGA I/O Ports).

  CPU Exception Interrupt  
286+ computer execute INT 0aH when the CPU is in protected mode and it
detects an Invalid Task Segment State during a JMP, CALL, IRET, or INT

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INT 0aH: IRQ 2 Cascade / Invalid Task State