custom instruction not working in 13.1.3

I just found the problem. The custom instruction slave translator terminates the 'b' input when 'readrb' is not present. So you might need to add readrb to the custom instruction and just not use it so that the 'b' signal gets hooked up correctly.

I just looked at the Nios II custom instruction userguide and there is very little information about which signals need other signals to be present so if adding readrb doesn't solve the problem then I suspect you'll have to add 'readra', 'a', 'writerc', and 'c'. The slave translator makes it look like a, b, and c are all independent but I'm not sure if the tools keep them seperate or if it's an all or nothing paramerization that it performs.

Either way I'll create a bug report since at a minimum this behavior should be at least documented.