Fastest Arduino DUE timer interrupts?

so found code on here utilizing due's timers create interrupt. after messing around see how fast can due flip portd values, switching high low on 1 pin @ 680.0 nanoseconds. wondering if there faster way this?

i have attached code , pasted below. apologize in advance if didn't provide enough information , simple copy , paste of code below. first post.

  void setup() {
  // put setup code here, run once:
  pinmode(14, output);
  pinmode(9, output);
  reg_piod_ower = 0x0060;
 
  starttimer(tc1,0,tc3_irqn, 100000);
 
}

void tc3_handler(){
    tc_getstatus(tc1, 0);
     
     reg_piod_odsr = reg_piod_odsr ^ 0x00000010;
     
}

void loop() {
}

void starttimer(tc *tc, uint32_t channel, irqn_type irq, uint32_t frequency){
   
    //enable or disable write protect of pmc registers.
    pmc_set_writeprotect(false);
    //enable specified peripheral clock.
    pmc_enable_periph_clk((uint32_t)irq);
     
    tc_configure(tc, channel,tc_cmr_wave|tc_cmr_wavsel_updown_rc|tc_cmr_tcclks_timer_clock1);//|tc_cmr_cpcstop);
    uint32_t rc = 1;//variant_mck/128/frequency;
     
    tc_setra(tc, channel, rc);
    tc_setrc(tc, channel, rc);
    tc_start(tc, channel);
     
    tc->tc_channel[channel].tc_ier = tc_ier_cpcs;
    tc->tc_channel[channel].tc_idr = ~tc_ier_cpcs;
    nvic_enableirq(irq);
}

that sounds entirely plausible, given overhead of calling interrupt routine.

what trying do?

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