Yes the interrupt number is 77 on A8 for mailbox interrupt. You need to call request_irq() function with interrupt number and your callback funtion. Look at implementation of syslink_x_xx_xx_xx\packages\ti\syslink\utils\hlos\knl\osal\Linux\OsalIsr.c. especially OsalIsr_install() also look at OsalIsr_create(), it creates the your callback as a kthread based bottom half function where you can do rest of the processing (execution of callback) when scheduled.