Legacy mode is selected when the Enable Performance Mode option in the Vivado Integrated Design Environment (IDE) is disabled. Legacy mode uses the AXI4-Lite interface and is fully backward compatible with all the older versions of the AXI Quad SPI core in terms of functionality, register bit placement, and register access.
The AXI Quad SPI core, when configured in standard SPI mode, is a full-duplex synchronous channel that supports a four-wire interface (receive, transmit, clock, and slave-select) between a master and a selected slave. When configured in Dual/Quad SPI mode, this core supports additional pins for interfacing with external memory. These additional pins are used while transmitting the command, address, and data based on the control register settings and command used.
The core supports the manual slave select mode as the default mode of operation for slave select mode. This mode allows manual control of the slave select line with the data written to the slave select register, thereby allowing transfers of an arbitrary number of elements without toggling the slave select line between elements. However, before starting a new transfer, the slave select line must be toggled.
The other mode related to slave select is automatic slave select mode. In this mode, the slave select line is toggled automatically after each element transfer (when FIFO is disabled). This mode, which is supported only in standard SPI mode, is described in more detail in SPI Protocol Slave Select Assertion Modes.
The core functionality is divided into standard SPI mode and dual and quad SPI mode. The functionality for each mode differs in the way the slave memory works.