The Usage of Custom_boot Pin

[Yuan Dai]

Hi,

I found a pin named "custom_boot" in the ChipTop, but I don't know the usage of it. In addition, it is set to 0 most of the time, including Simulation flow and FPGA prototype. It seems there is no document to introduce this usage of "custom_boot," so I'm kindly asking about it.

Thanks & Regards,
 
Yuan

[Jerry Zhao]

If driven, CustomBootPin will write an alternative physical address (specified at elaboration time) into the BootAddrReg, providing an easy way to select between two boot paths.
The default value in BootAddrReg is usually the base of DRAM (0x80000000). 
The default alternate physical address is also usually the base of DRAM (0x80000000) (meaning that in default configs asserting custom_boot will cause no difference in behavior).

You can override the default alternate address of CustomBootPin with some configuration fragment. See the source code for CustomBootPin in testchipip for details.

-Jerry

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[Yuan Dai]

Hi Jerry,

Thanks for your reply, which is helpful. I will learn more about the source code of it.

Best regards,

Yuan