09:07 <nengel> When instantiating 3rd-party verilog modules in migen, how do I put constants of a specific bit-width on inputs?

09:20 <ysionneau> you could declare a Signal(N) for instance which would be "N bits wide"

09:20 <ysionneau> and you can use that Signal as an input of the instanciation

09:20 <ysionneau> for an example of verilog instanciation from Migen : https://github.com/m-labs/misoc/blob/master/misoclib/lm32/__init__.py

09:21 <ysionneau> look at how it creates the self.interrupt Signal(32) and how it is passed to the lm32 instance

09:23 <ysionneau> it seems there is also this kind of syntax : https://github.com/m-labs/misoc/blob/master/misoclib/minimac3/__init__.py#L48

09:23 <ysionneau> I don't know which one is the preferred one

09:24 <ysionneau> and if your signal is constant, just put comb += yoursignal.eq(constante value)

09:48 <nengel> thanks. I assume the PreformattedParam only works for parameters (as they can be strings)?

11:21 <sb0> nengel, PreformattedParam is only required when you want to override the normal way Migen prints out constants

11:22 <sb0> here it's used to make sure the value of the p_eba_reset parameter is always 32-bit wide (because values other bit widths tickle bugs in the lm32 verilog)

11:22 <sb0> otherwise, migen would use the minimum number of bits required to represend eba_reset

11:25 <sb0> if your verilog design doesn't have such bugs, you should not need PreformattedParam

11:25 <nengel> yes, that is the exact problem I was having

11:26 <sb0> better use "wire [expected bit width] _parameter = parameter;" somewhere in the verilog

11:26 <nengel> it's a parameter (generic), not a wire

11:26 <sb0> then parameter is automatically zero- or sign-extended

11:27 <nengel> and I'm not writing the verilog

11:27 <sb0> yes but you can make it a wire before using it

11:27 <nengel> no because I don't use it

11:27 <sb0> but in some cases (like lm32) it's messy, which is why there's PreformattedParam

11:27 <sb0> which is also messy, but less

11:28 <nengel> I give a parameter to an instance, which copies that parameter to a sub-instance, which accesses a bitrange of the parameter.

11:28 <nengel> which gives an error if it's not at least 9 bit wide.

11:29 <sb0> yes. that's a common problem. you can assign it to a 9-bit wire in the sub-instance, and slice that.

11:29 <nengel> I'm not touching the sub-instance

11:29 <nengel> I'm not touching the instance

11:29 <nengel> not my circus, not my monkeys