[myhdl-list] Restrictions for conversion

[Oscar D. <osc...@gm...>]

Hi

I was doing some experiments with the conversion function, and I found
a problem I'd like to discuss regarding access to members of data
structures inside generators. Suppose you have a dict with some
constants you need for the calculations:

constants_list = {"myconst": 10}
def trans_block(clk, din, dout, const_list):
    @always(clk.posedge)
    def proc():
        dout.next = din + const_list["addconst"]
    return instances()

conversion fails with:
myhdl.ConversionError: in file simpletest.py, line 22:
    Object type is not supported in this context: const_list, <type 'dict'>

Same occur if you have a list:
myhdl.ConversionError: in file simpletest.py, line 22:
    Object type is not supported in this context: const_list, <type 'list'>

Or, even if you use an object with members accessed as attributes, like this:
        dout.next = din + const_list.addconst
conversion fails with:
myhdl.ConversionError: in file simpletest.py, line 29:
    Unsupported attribute: addconst

A workaround is to access data outside the generator, with another
variable name:

constants_list = {"myconst": 10}
def trans_block(clk, din, dout, const_list):
    addconst = const_list["addconst"]
    @always(clk.posedge)
    def proc():
        dout.next = din + addconst
    return instances()

However, it's kind of annoying to do that when you have a lot of
variables to access. Something similar occurs when you access signals.

What are your thoughts? Is it good to allow access data members
whatever way you want or is better to have a fixed coding style? By
the way, I think these kind of details should be explained in the
conversion documentation.

Best regards

-- 
Oscar Díaz
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