Potential forbidden axi write handshake dependency in debugging unit (#182)

[barrydebruin]

Hi,

Since I've opened this issue on an axi handshaking issue in the interconnect, there has not been provided a fix yet, despite the issue being closed. The details of the problem can be found here: https://github.com/pulp-platform/pulpino/issues/182.

To summarize, the AXI interconnect contains a false dependency between AWVALID and WVALID. More specifically, it breaks the following condition (see AXI4 standard): 'the master must not wait for the slave to assert AWREADY or WREADY before asserting AWVALID or WVALID'

This pull request seems to fix this issue for me. Please do check the existing functionality for yourself as well, as I did not run this thing through a protocol checker yet.

Kind regards,

Barry

[zarubaf]

Sadly this issue is really annoying, I've been stumbling over this as well and loosing time. Sorry that that happened to you as well. We will have a look at a your fix.
The "easy" workaround so far for us has been to instantiate slices around the interconnect.