This chapter provides a primary boot mode summary, selection considerations, and interface information.
Each boot mode uses a set of I/O pins and has a voltage requirement that can affect post-boot peripheral use of shared MIO signals on a bank. The best overall boot mode solution for an application considers the overall system requirements, performance, cost, and complexity.
The boot modes are categorized into autonomous or supervised boot modes. The autonomous boot modes automatically load the programmable device image from a memory source (SD, eMMC, QSPI, or OSPI). The autonomous boot modes provide a basic solution with easy setup. In autonomous boot modes, the POR_B pin release to the first fetch from a boot device is estimated at ~620 μs. This time guides how quickly the flash must be ready to respond to the BootROM. The supervised boot modes require an external processor or controller to load the programmable device image with a command set (JTAG or SelectMAP). An advantage of using a supervised boot mode is that the device image can reside almost anywhere in the host system or over a network connection. The supervised boot modes are multipurpose interfaces that can also be used for system debug.
For systems that require a low-cost solution, QSPI boot modes are ideal with a variety of second -source vendors. For applications that require faster boot times due to power-on latency constraints, the boot modes with wide bus widths are inherently faster. For the boot modes, the QSPI dual-parallel 8-bit or OSPI 8-bit is an optimal choice for a faster boot time.
For supervised boot modes, the SelectMAP 32-bit interface provides the fastest boot time option. For applications with large storage capacity requirements, the SD and eMMC boot modes support larger boot memory devices.
The MIO-at-a-glance tables should be reviewed to ensure that the requirements for boot and post-boot peripherals are satisfied. This chapter focuses on the primary boot mode options. However, the Versal adaptive SoC is capable of starting with a primary boot mode and then switching to a secondary boot option (that is, QSPI primary boot, followed by USB as a secondary boot option). See the Versal Adaptive SoC System Software Developers Guide (UG1304) for more information on secondary boot options. Boot modes that are secure boot capable support both asymmetric and symmetric Hardware Root of Trust modes.