Intel® Arria® 10 Hard Processor System Technical Reference Manual

ID 683711
Date 8/28/2023
Public
Document Table of Contents

22.5.6. Receive FIFO 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 = decoded watermark level of IIR_FCR.RT + 1

If the number of data items in the receive FIFO is equal to the source burst length at the time of the burst request is made, the receive FIFO 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, decoded watermark level of IIR_FCR.RT. †

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

The receive FIFO is not be empty at the end of the source burst transaction if the UART controller has successfully received one data item or more on the UART serial receive line during the burst. †

Figure 147. Receive FIFO Buffer