Re: [myhdl-list] Tristate bus to external SRAM
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jandecaluwe
From: George P. <ge...@ga...> - 2006-09-01 14:53:33
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>> Maybe I should be more clear. I'm looking to create a >> *bidirectional* >> bus to an external SRAM chip. I suppose somehow the output driver >> needs to get tristated when the the bus is in input mode. I'm not >> sure how to bring this about, or if the fpga software tool will infer >> this for me, etc. > But you are talking about off-chip of course. Let's separate > the issues: > Verilog conversion support > -------------------------- > > Nothing has been done. At least 2 things would be needed: > 1) convert a None constant value to 'Z' > 2) infer inout ports at the top-level interface when > an interface signal is used as such. > > In addition, it would be nice to know what templates are > exactly supported by the mainstream fgpa synthesis tools > to infer tristates, tristate ports, and bidirectional ports. > This may influence Verilog conversion choices. > > Because of 2), you cannot simply use the user-defined verilog > feature to specify the verilog code you want yourself. > I fear the workaround at this point is a manually written > top-level Verilog wrapper, as suggested elsewhere. > Great to hear from you again Jan! I will try out your and Gunter's suggestions. What I'd like is an automatic way to combine the myhdl code with a user-supplied top-level Verilog wrapper. This might be doable with shell scripting and/or make, but being able to specify the wrapper filename inside the myHDL code sounds like a better way right now. MyHDL could automatically incorporate the wrapper into its Verilog output. I'll have to experiment a bit to be sure, but what do you think? > For a possible implementation of the features discussed > above, I need feedback from users to find out and specify > exactly what needs to be done, and how urgent it is. > I'll be glad to give you any feedback I can. I'm starting to create a VGA controller in my FPGA, and in a while, I'll need to access external RAM := ) Peace, George Pantazopoulos http://www.gammaburst.net |