On Wed, Jan 14, 2015 at 5:20 AM, Tomasz Wlostowski < tomasz.wlostow...@cern.ch> wrote:
> Hi all, > > During my work on diff pairs/matched length tools, I've encountered a > rather tricky problem: as the diff pair gap specific to a particular > pair of traces is stored nowhere, the shove algorithm will mess up DP > coupling after saving and re-loading the board. Ergo: the DP gaps (and > possibly other settings) need to be stored somewhere in .kicad_pcb > files. Perhaps in a yet another s-expr token. > > The problem is that adding any new token to the file format causes all > precedent versions of pcbnew to drop an error attempting to load the > file. I would propose two solutions to overcome this: > - (a dumb one) if the version in the file header is newer than the > version supported by the running application, issue warnings instead of > fatal errors on unknown tokens, > - (a bit smarter) enclose all optional tokens in a "minimum" version > block ( min_version version_number ( optional_token ( ... ) ) ) that > would be ignored if the application version < version_number. > > I consider this modification quite important from the point of view of > adding future features and the upcoming stable version: if we keep > things as they are, adding any new feature will either make the files > unreadable to the stable version or force us to support saving in > multiple format versions. > > Looking forward to your feedback, > Tom > I would prefer to do what had been done in the past - simply increase the File Version number and don't expect earlier versions to support the new features (or to read the board at all). What we *can* safely do is check the file version number when parsing and if the parser does not recognize it then we can display a message to say that it is a newer file version and we cannot read it. If people are collaborating and this can be an issue then they must agree on a version of KiCad to use; after all in most cases they can build any historical version from the past 2 years. - Cirilo
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