Intel® Arria® 10 Hard Processor System Technical Reference Manual

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

21.5.5.1. Transmit FIFO Underflow

During I2C serial transfers, transmit FIFO requests are made to the DMA controller whenever the number of entries in the transmit FIFO is less than or equal to the value in DMA Transmit Data Level Register (IC_DMA_TDLR), also known as the watermark level. The DMA controller responds by writing a burst of data to the transmit FIFO buffer, of length specified as DMA burst length. †

Note: Data should be fetched from the DMA often enough for the transmit FIFO to perform serial transfers continuously, that is, when the FIFO begins to empty, another DMA request should be triggered. Otherwise, the FIFO runs out of the data (underflow) causing the maser to stall the transfer by holding the SCL line low. To prevent this condition, you must set the watermark level correctly.†