GAP8 E-FUSE SETTINGS FOR RELIABLE BOOT Application Note
●INTRODUCTION
■By default, GAP8 expects code to be downloaded into its internal RAM through its JTAG interface and will boot from there.
■Whilst this is convenient for initial board bring-up, in a product GAP8 would normally boot from another source.
■Three main alternative boot mechanisms are offered with GAP8:
▲boot from an external HyperFlash connected to GAP8’s HyperBus interface
▲boot from an external SPI Flash connected to GAP8’s SPIM0 interface (this would typically be a Quad-SPI capable Flash to get decent throughput)
▲boot from SPI Slave interface (this is an unsecured boot, although it may be handy in some cases – more details later).
■Upon power-up, a primary boot code located in ROM is executed. This code performs a number of initial checks and configurations and then gets a secondary boot code (start of user’s application) from the selected external source, copies it into the internal L2 RAM and executes it.
■Selection of the source for booting is done through the programming of a specific e-fuse. In addition, a minimal set of additional e-fuses must be programmed for reliable boot, they control the behavior of some important checks and configurations performed by the primary boot code.
■Programming an e-fuse bit consists of burning the associated fuse; once burnt the e-fuse is permanently set to the selected value and cannot be modified anymore. Fuse programming typically occurs at board production or commissioning. Some ‘user” fuses are also available to be used freely by the application.
■GAP8’s SDK includes a fuse programming utility that enables the user to specify an array of fuses to be burnt.
■The next sections in this document detail what fuses should be programmed for proper boot. Reference is made to e-fuse bits listed in a map provided as Appendix. In the interest of clarity, only those e-fuses useful to customers are made explicit. Others are marked “Reserved”; they typically correspond to options reserved for alternative configurations of GAP8 or for future use. The table will be updated if some of those reserved fuses actually need to be activated in the future.
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Application note & Design Guide |
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Please see the document for details |
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English Chinese Chinese and English Japanese |
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Feb.2021 |
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Version: Rel.1.2 |
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AN004 |
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464 KB |
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