This answer record contains supplemental information to describe new parameters introduced to the SEM v3.5 (in ISE) example designs EXT shim to support larger densities of SPI Flash.
For the Vivado core, this information is in the SEM v4.0 Product Guide. For ISE, the information is provided in this answer record. Also, included at the bottom of the document is the list of SPI Flash devices which have been used in SEM hardware testing. For the Vivado core, this information is in the SEM v4.0 Product Guide in the Verification section.
The External Interface consists of four signals implementing a SPI bus protocol compatible, full duplex serial port. This interface is only present when one or both of the following controller options are enabled:
The implementations of these functions require external storage. The system-level design example provides a fixed-function SPI bus master in the EXT shim to fetch data from a single external SPI Flash device.
The EXT shim uses the fast read command (0x0b) and can be configured to support one of several different families of SPI Flash. The family supported by default depends on the external storage size requirements. In the EXT shim system-level example design module, there are three parameters that control the command sequence sent to the SPI Flash device.
For storage requirements less than or equal to 128 Mbits, the EXT shim supports M25P devices by default (B_ISSUE_WREN = 0, B_ISSUE_WVCR = 0, B_ISSUE_EN4B = 0). These devices are not capable of four-byte addressing mode.
For storage requirements greater than 128 Mbits, the EXT shim supports higher-density N25Q devices by default (B_ISSUE_WREN = 1, B_ISSUE_WVCR = 1, B_ISSUE_EN4B = 1). These devices are capable of four-byte addressing mode.
Other supported devices include lower-density N25Q devices for storage requirements less than or equal to 128 Mbits (B_ISSUE_WREN = 1, B_ISSUE_WVCR = 1, B_ISSUE_EN4B = 0) and higher-density MX25 devices for storage requirements greater than 128 Mbits (B_ISSUE_WREN = 0, B_ISSUE_WVCR = 0, B_ISSUE_EN4B = 1).
The SPI Flash devices used in the SEM core hardware verification platform include: