Intel® Agilex™ Hard Processor System Technical Reference Manual

ID 683567
Date 2/14/2023
Public

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20.5.5.3. Transmit FIFO Overflow

Setting the DMA burst length to a value greater than the watermark level that triggers the DMA request might cause overflow when there is not enough space in the transmit FIFO to service the destination burst request. Therefore, the following equation must be adhered to in order to avoid overflow: †

DMA burst length <= FIFO_DEPTH - IC_DMA_TDLR

In case 2: IC_DMA_TDLR = 48, the amount of space in the transmit FIFO at the time of the burst request is made is equal to the DMA burst length. Thus, the transmit FIFO may be full, but not overflowed, at the completion of the burst transaction. †

Therefore, for optimal operation, DMA burst length should be set at the FIFO level that triggers a transmit DMA request; that is: †

DMA burst length = FIFO_DEPTH - IC_DMA_TDLR

Adhering to this equation reduces the number of DMA bursts needed for block transfer, and this in turn improves bus utilization. †

The transmit FIFO may not be full at the end of a DMA burst transfer if the I2C controller has successfully transmitted one data item or more on the I2C serial transmit line during the transfer. †