Cast reset value for transparent read ports to integer

[adamgreig]

Currently if you pass a list of items which can be converted to an integer but are not integers (for example, numpy.int64 objects), they are converted when used to initialise Memory._array, but a transparent read port sets its reset value to mem.init[0], which is not cast.

This eventually causes VcdWriter to bomb out because it checks isinstance(value, int) which fails for numpy.int64.

This PR uses operator.index to cast the value to an integer, the same way it's done inside the init setter when creating Memory._array.

Test case:

import numpy as np
import nmigen as nm
from nmigen.back import pysim


class Foo(nm.Elaboratable):
    def __init__(self):
        self.idx = nm.Signal(7)
        self.out = nm.Signal(8)

    def elaborate(self, platform):
        data = np.arange(128, dtype=np.int)
        mem = nm.Memory(width=8, depth=128, init=data)
        print(type(mem._array[0].reset))
        m = nm.Module()
        # Change to transparent=False to avoid use of Mem.init[0]
        rp = mem.read_port(transparent=True)
        m.submodules += rp
        m.d.sync += rp.addr.eq(self.idx), self.out.eq(rp.data)
        return m


mod = Foo()


def testbench():
    yield
    for i in range(10):
        yield mod.idx.eq(i)
        yield
        print((yield mod.out))
        yield


sim = pysim.Simulator(mod)
sim.add_clock(1e-6)
sim.add_sync_process(testbench)
with sim.write_vcd("test.vcd"):
    sim.run()

Traceback:

Traceback (most recent call last):
  File "test.py", line 37, in <module>
    with sim.write_vcd("test.vcd"):
  File "/home/adam/.local/lib/python3.6/site-packages/nmigen-0.3.dev63+gd90f0fe-py3.6.egg/nmigen/back/pysim.py", line 1124, in write_vcd
    vcd_file=vcd_file, gtkw_file=gtkw_file, traces=traces)
  File "/home/adam/.local/lib/python3.6/site-packages/nmigen-0.3.dev63+gd90f0fe-py3.6.egg/nmigen/back/pysim.py", line 124, in __init__
    var_type=var_type, size=var_size, init=var_init)
  File "/home/adam/.local/lib/python3.6/site-packages/vcd/writer.py", line 282, in register_var
    raise ValueError('vector init value must be int, bool, str, or None')
ValueError: vector init value must be int, bool, str, or None

[adamgreig]

Alternatively we could use

            if len(self.memory._array) > 0:
                self.data.reset = self.memory._array[0].reset

rather than doing the cast again (although it should succeed, since a failure would have been caught the first time).

[whitequark]

Thanks!