How to read back the AES key from eFuse?

[f.m.dostoevsky-the-embedder]

Subject is clear.

My board is a 7020; and AES key is in eFuse registers. I've not programmed the R_EN_B_Key (Disables reading of AES key); so I assume I must be able to read it back. But how?

Thanks,

Dosto

[ddn · Accepted solution]

Hi @f.m.dostoevsky-the-embedder ,

Xilinx doesn't recommend AES Key readback.

For security reasons, there is no Vivado Tcl command to read the 7 series AES key.

eFUSE registers can be read through JTAG ports. Table 5-18 lists eFUSE-related JTAG instructions. Refer page 104 of UG470 (v1.13.1).

Hope this helps.

Regards,

Deepak D N

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[f.m.dostoevsky-the-embedder]

Thank you @ddn!

Why it is not recommended?

I'm trying to get it through JTAG according to your reply. It looks like I have to deal with `jtag sequence`s which I couldn't make happen so far. This is the TCL I wrote using so few examples around the web; which prints 8 byte random data followed by ff's (like 1122334455667ffffffffffffffffffffffffffffffffffffffffffffffff) as the output eventhough I try it for different registers and bit sequences.

set seqname [jtag sequence]
$seqname state RESET
$seqname irshift -register fuse_cts_slr0
#$seqname irshift -bits 6 110001
$seqname drshift -capture 256
set result [$seqname run -hex]
puts $result
$seqname delete

Could you please guide me through reading it back? I cannot boot my module and have to check whether the key is properly written or not.