Arria V Hard Processor System Technical Reference Manual

ID 683011
Date 12/02/2022
Public
Document Table of Contents

20.5.6.6. Receive FIFO Buffer Underflow

Setting the source transaction burst length greater than the watermark level can cause underflow where there is not enough data to service the source burst request. Therefore, the following equation must be adhered to avoid underflow: †

DMA burst length = DMATDLR + 1

If the number of data items in the receive FIFO buffer is equal to the source burst length at the time of the burst request is made, the receive FIFO buffer may be emptied, but not underflowed, at the completion of the burst transaction. For optimal operation, DMA burst length should be set at the watermark level, DMATDLR + 1. †

Adhering to this equation reduces the number of DMA bursts in a block transfer, which in turn can improve bus utilization. †

Note: The receive FIFO buffer is not be empty at the end of the source burst transaction if the SPI controller has successfully received one data item or more on the serial receive line during the burst. †
Figure 105. Receive FIFO Buffer