Onboard general purpose timer resolution for the ADSP-SC589

We need a 500ns interrupt to drive our software loop, and were wondering if the onboard general purpose timers for either the Arm processor or the Sharc boards on the ADSP-SC589 SOC could provide this ?

I have been experimenting with the general purpose timer for the Sharc board, and am getting some unexpected results.

I am using mode  ADI_TMR_MODE_CONTINUOUSE_PWMOUT, clock source ADI_TMR_CLKIN_SYSCLK, Irqmode ADI_TMR_IRQMODE_WIDTH_DELAY, Period = 200, width = 100, and delay =100.

I would expect an interrupt every 200 cycles, but am seeing one every 806 cycles.

Thanks !