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Or any other suggestions to implement ISP function?
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It depends on whether you want remote update of your SPI.
Daixiwen's suggestion assumes that your SPI flash has been configured once, so that your FPGA configures, or that you have JTAG to configure your FPGA.
If you want to ensure that your SPI flash can be programmed regardless of whether the FPGA is configured, then your microcontroller needs to be able to "take over" the SPI interface.
You can deassert nCE and assert nCONFIG to "reset" an FPGA. This is what the AS cable does.
Your design can attach the SPI flash directly to your microcontroller, or through a tri-state buffer. When you want to program the SPI flash, your micro can reset the FPGA, and then program the SPI flash directly.
Ideally you should connect both the SPI flash and the FPGA JTAG to your microcontroller, as then both options are available, and you will be able to access JTAG debug components.
Cheers,
Dave
Honored Contributor
