Timer interrupt frequency Limit ?

[leeyoungjae]

HI

I am using Timer1 to generate an interrupt at every 0.125 us ( 8MHz timer counter )

I modify timer setup code of Periph_blinky in LPCOpen.

Problem : I couldn’t generate an INT at Every 0.125us even through modify timer match value

MCU : LPC4370

Test Board: LPC-Link2 (included LPC4370)

Please check the following code that is set up timer INT for 0.125us (micro second)

static void timer_setup(void)

{

       /* Enable timer 1 clock and reset it */

       Chip_TIMER_Init(LPC_TIMER1);

       Chip_RGU_TriggerReset(RGU_TIMER1_RST);

       while (Chip_RGU_InReset(RGU_TIMER1_RST)) {}

       /* Timer setup for match and interrupt at SAMPLERATE */

       Chip_TIMER_Reset(LPC_TIMER1);

       Chip_TIMER_MatchEnableInt(LPC_TIMER1, 1);

//     Chip_TIMER_SetMatch(LPC_TIMER1, 1, (Chip_Clock_GetRate(CLK_MX_TIMER1) / SAMPLERATE));

// Chip_Clock_GetRate(CLK_MX_TIMER1): 204000000

// SAMPLERATE : 5

// Modified code for 0.125us (8MHZ) timer INT

Chip_TIMER_SetMatch(LPC_TIMER1, 1, (Chip_Clock_GetRate(CLK_MX_TIMER1) / 25000000 ));

       Chip_TIMER_ResetOnMatchEnable(LPC_TIMER1, 1);

       Chip_TIMER_Enable(LPC_TIMER1);

       /* Enable timer interrupt */

       NVIC_EnableIRQ(TIMER1_IRQn);

       NVIC_ClearPendingIRQ(TIMER1_IRQn);

}

result frequency: 1.6MHz (maximum).

Question

1. Is there any limit for timer Interrupt frequency ?

- I want to generate 8Mhz timer Interrupt

2. How can I generate timer Interrupt at every 0.125us ( 8MHz ) ?

Thanks for you review.

[jamn]

Had you solved this Problem? I face the same question. Thanks!

[jeremyzhou]

Hi LEE Young Jae,

Thank you for your interest in NXP Semiconductor products and 

the opportunity to serve you.

1. Is there any limit for timer Interrupt frequency ?

    Yes, it's up to the CLK_M4_TIMER0, as illustrated in the Table 780 in the reference manual.

2. How can I generate timer Interrupt at every 0.125us ( 8MHz ) ?

    You need to increase the system clock frequency as quick as possible, the 204 MHz is maximum, then simplify the interrupt function as 00125us doesn't allow any extra operation.

Hope it helps.

Have a great day,

TIC

-----------------------------------------------------------------------------------------------------------------------
Note: If this post answers your question, please click the Correct Answer button. Thank you!
-----------------------------------------------------------------------------------------------------------------------

[jamn]

 My clock is 204MHz, but I get only 2MHz. Could you tell me anything to do? Thanks!

[frank_m]

Having an interrupt at a 8MHz rate is a very bad idea. Each interrupt invokes the saving and restoring of the context, which is 12 cycles each without FPU registers.

This eats away core performance. And even with a moderate handler routine, you will quickly reach the saturation point.

[jamn]

Thanks! That is right, I got it.