LPC1788 DMA Delay Problem

[Persian_Men]

Hi Everyone
i have a problem with LPC1788 DMA
i want transfer data linked list from sram to gpio port by DMA.
i try this code and work correctly
but i have a big problem
in data logger result you can see huge time gap between each transfer completed.

test code:

void DMA_IRQHandler (void)
{
	static uint32_t regVal;
	regVal=LPC_GPDMA->IntTCStat;
	LPC_GPDMA->IntTCClear |= regVal;
	regVal=LPC_GPDMA->IntErrStat;
	LPC_GPDMA->IntErrClr |= regVal;
	
	// check GPDMA interrupt on channel DMA_CHANNEL_NO
	//if (GPDMA_IntGetStatus(GPDMA_STAT_INT, DMA_CHANNEL_NO)){ //check interrupt status on channel DMA_CHANNEL_NO
		// Check counter terminal status
		//if(GPDMA_IntGetStatus(GPDMA_STAT_INTTC, DMA_CHANNEL_NO)){
			// Clear terminate counter Interrupt pending
			//GPDMA_ClearIntPending (GPDMA_STATCLR_INTTC, DMA_CHANNEL_NO);
			//Channel0_TC++;
		//}
	//}
}

GPDMA_LLI_Typd					GPDMA_LLI;

void DMA_Setup()
{
		uint32_t	i=0;
		GPDMA_Channel_CFG_Type	GPDMACfg;
	
		for (i=0;i<512;i+=2)
		{
			DMASrc_Buffer[i]=0x00;
			DMASrc_Buffer[i+1]=0xff;
		}
		
		NVIC_DisableIRQ(DMA_IRQn);
	
		NVIC_SetPriority(DMA_IRQn, ((0x01<<3)|0x01));
	
		GPDMA_Init();
		//Setup DMA Channel
	
		GPDMA_LLI.SrcAddr=(uint32_t)DMASrc_Buffer;
		GPDMA_LLI.DstAddr=(uint32_t)&(LPC_GPIO0->PIN);
		GPDMA_LLI.NextLLI=(uint32_t)&GPDMA_LLI;
		GPDMA_LLI.Control= DMA_SIZE 
											|		(2<<18) //SW=32Bit
											|		(2<<21)	//DW=32Bit
											|		(1<<26) //source incr
											|		(1<<31) ;
		
		GPDMACfg.ChannelNum=DMA_CHANNEL_NO;
		GPDMACfg.SrcMemAddr=(uint32_t)DMASrc_Buffer;
		GPDMACfg.DstMemAddr=(uint32_t)(&LPC_GPIO0->PIN);

		// Transfer size
		GPDMACfg.TransferSize = DMA_SIZE;
		// Transfer width
		GPDMACfg.TransferWidth = GPDMA_WIDTH_WORD;
		// Transfer type
		GPDMACfg.TransferType = GPDMA_TRANSFERTYPE_M2M;
		// Source connection - unused
		GPDMACfg.SrcConn = 0;
		// Destination connection - unused
		GPDMACfg.DstConn = 0;
		// Linker List Item - unused
		GPDMACfg.DMALLI = (uint32_t)&GPDMA_LLI;
		// Setup channel with given parameter
		GPDMA_Setup(&GPDMACfg,0);

		// Enable GPDMA channel DMA_CHANNEL_NO
		GPDMA_ChannelCmd(DMA_CHANNEL_NO, ENABLE);
		
		/* Enable GPDMA interrupt */
		NVIC_EnableIRQ(DMA_IRQn);

}

my problem is huge time between each transition.
you can see in this picture
A section period time and B section is same.
i don't know why this time gap happened.
thanks for your help