NXP Semiconductors QorIQ LS1012A Reference Manual

26.7.2.2 Flexible AHB buffersIn order to reduce the latency of the reads for AHB masters, the data read from the serialflash is buffered in flexible AHB buffers. There are four such flexible buffers. The size ofeach of these buffers is configurable with the minimum size being 0 Bytes and maximumsize being the size of the complete buffer instantiated.The size of buffer 0 is defined asbeing from 0 to QSPI_BUF0IND. The Size of buffer 1 is from QSPI_BUF0IND toQSPI_BUF1IND, buffer2 is from QSPI_BUF1IND to QSPI_BUF2IND and buffer 3 isfrom QSPI_BUF2IND to the size of the complete buffer, which is given in the chip-specific QuadSPI information.Each flexible AHB buffer is associated with the following1. An AHB master. Optionally, buffer3 may be configured as an "all master" buffer bysetting the QSPI_BUF3CR[ALLMST] bit. When buffer3 is configured in such away, any access from a master not associated with any other buffer is routed tobuffer3.2. A datasize field representing the amount of data to be fetched from the flash on every"missed" access.The master port number of every incoming request is checked and the data is returned/fetched into the corresponding associated buffer. Every "missed" access to the buffercauses the controller to clear the buffer and fetch QSPI_BUFxCR[ADATSZ] amount ofdata from the serial flash.As such, there is no benefit in configuring a buffer size ofgreater than ADATSZ, as the locations greater than ADATSZ will never be used. For anyAHB access, the sequence pointed to by the QSPI_BFGENCR[SEQID] field is used forthe flash transaction initiated. The data is returned to the master as soon as the requestedamount is read from the serial flash. The controller however, continues to prefetch therest of the data in anticipation of a next consecutive request. Figure 26-3 shows theflexible AHB buffers.The QSPI_BFGENCR[SEQID] field points to an index of the LUT. Refer to Look-upTable for details.Chapter 26 Quad Serial Peripheral Interface (QuadSPI)QorIQ LS1012A Reference Manual, Rev. 1, 01/2018NXP Semiconductors 1481