[Libre-soc-dev] gtkwave diff, was “daily kan-ban update 11jan2022”

lkcl luke.leighton at gmail.com
Tue Jan 11 19:28:38 GMT 2022

On Tue, Jan 11, 2022 at 7:07 PM Richard Wilbur <richard.wilbur at gmail.com> wrote:
> What data is gtkwave displaying?

signal traces.

> How is it stored?

in ASCII format.  it's common to see vcd files increasing over
10 megabytes per second.  a 1 gigabyte file can be created
in under 30 seconds.

turns out that there is a program called "vcddiff".

however i found the source of the problem by a manual comparison:

* loadstore asks dcache to do a store.  it has no PTE so MMU is notified
* MMU triggered some RADIX lookups, dcache does a batch of QTY 8
  wishbone LDs, but it can reply *early* (once one of those 8 LDs
  gives the data needed).
* *whilst dcache is still waiting for some of the remaining LDs*
  the store is continued.
* store goes, "oh look, i got an ACK from wishbone, that's all great:
  i'll just drop the store on the floor then"


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