JTAG write to Node Config registers?

[steveM]

I can use JTAG on a startkit to read/write tile configuration (pswitch) registers (giving access to debug etc), and can read from node configuration (sswitch) registers, but writing fails. I've also tried with the same outcome on a couple of G4s, and have tried (again unsuccessfully) using Segher's excellent jtag tools.Has anyone successfully written node configuration registers over JTAG? What does it require (other than changing the read command '0b01' to the write command '0b10' in the 10 bit IR register)?