Custom Components and VHDL Code

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originally posted by shmueld@Mar 12 2006, 08:27 PM

i have just started to design with the sopc builder. could someone please explain to me how the vhdl code placed in a custom component relates to the outside world and the avalon bus/nios ii microprocessor. specifically - how does the addressing work - if i want, lets say, set a specific signal high at a specific address - do i need a chip select within the vhdl ? do i need to incorporate an address into my vhdl code ? how does the base address of the component relate to my vhdl code and will the following code work without any address decoding within the vhdl :-

ouputsignal <= &#39;1&#39; when cs = &#39;1&#39; and write =&#39;1&#39; else &#39;0&#39;;

could this type of functionality be incoporated into the custom component without any vhdl code ?

also could someone please explain to me the purpose of adding the software files to the custom component - does this create an address offset for different signals or is it just used for driver purposes ?

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1) If You want to placed your custom component to SOPC builder firstly you should read the manual "Quartus II Version 5.1 Handbook

Volume 4: SOPC Builder

5. Component Editor"

and, of course, the manual "Avalon Bus Specification"

2) Address decoding works like that

for example(Sorry for Verilog HDL http://forum.niosforum.com/work2/style_emoticons/<#EMO_DIR#>/smile.gif )

//regs of custom component

if(chipselect & write)

begin

case(address[2:0])

3&#39;d0:r0<=#1 writedata;

3&#39;d1:r1<=#1 writedata;

3&#39;d2:control0<=#1 writedata;

3&#39;d3:adr0<=#1writedata;

3&#39;d4:size0<=#1writedata;

3&#39;d5:control1<=#1 writedata;

3&#39;d6:adr1<=#1writedata;

3&#39;d7:size1<=#1writedata;

endcase

end

But, if You want component with one output

you should write as like you have already written in your message, I mean:

OUPUTsignal <= datawrite(0) when CS = &#39;1&#39; and WRITE =&#39;1&#39;;

this code writes bit 0 from avalon bus to output world.

3) Adding the software files to the custom component is adding functionality to your componets - initializations, calling and etc(drivers :-))

and does not create any an address offset&#39;s for it.

An address offset and base address are setting in SOPC Builder only.