Dick, On Fri, 25 Nov 2011, Dick Hollenbeck wrote:
> > *) Metric Board. This is a pcb board that has a great number of coordinates > and > distances that happen to be some multiple of the BIU that is also a multiple > of > a metric engineering unit such as micrometers. > > *) Imperial Board. This is a pcb board that has a great number of > coordinates and > distances that happen to be some multiple of the BIU that is also a multiple > of > an imperial engineering unit such as mils or inches. What is the purpose of this distinction? This is in fact scary. No boards are designed solely on a metric only imperial only grid anymore. All are designed on a mixed grid. The scary part is EDA programs that used to make you choose between a metric or imperial grid before laying out the first component. > Format Strings: > ============== > > #if USE_DOUBLE_BFU > typedef double BFU; > #define FMT_ENG ".%6g" > #else > typedef long double BFU; > #define FMT_ENG ".%6Lg" > #endif > > A format string can then be built up using compile time concatenation of > strings, like this: > > fprintf( fp, "Value: " FMT_ENG " " FMT_ENG "\n", BFU( biu1 * scale), BFU( > biu2 * scale ) ); Format strings had better be at least "%.10g" so that no precision is lost when writing BFU to disk. > > Here are the required immediate need BOARD load functions: > > 1) Legacy to deci-mil loader. This loader uses a floating point scaling factor > of unity, since destination is a RAM BOARD using deci-mils as its BIU. > > 2) Legacy to nanometer loader. This loader uses a floating point scaling > factor > of ________, since destination is a RAM BOARD using nanometers as its BIU, and > the source format is using deci-mils. > > 3) mm to nanometer loader. This loader uses a floating point scaling factor > of 1000000, since the destination is a RAM BOARD using nanometers as its BIU. > > There is no need for a nm to deci-mil loader. (Once somebody saves a file in > the > new format, that format is used going forward, or its backup in the old > format.) > > Now duplicate the above 3 loader types for MODULEs. The foregoing makes it appear that all that has to be done to load a board or module that was saved in the old deci-mil format is to apply the (2540) scaling factor and one is done. This is far from the case. The old format saves every metric spaced or sized part with pads in the wrong locations and incorrect sizes. Simply applying a scaling factor results in every metric spaced pad being very precisely in the wrong location and very precisely the wrong size, and the conversion will have accomplished nothing. This is true both of modules and boards. When I converted the internal unit to nanometers I provided a dialog on load of a deci-mil board that provided the user the option of resnapping points to a mixed grid and setting the minimum grid for imperial and metric snapping. That is, every point that is off the minimum imperial grid and is within the deci-mil round-off error of the minimum metric grid would be resnapped to the metric grid when loading. That's locations; the same was true for sizes of things. Locations of things that are absolutely placed on the board (e.g. tracks, module positions) used the board axis for resnapping. Locations of pads and other features within a module, used the module axis for resnapping. Of course the user could decide not to resnap. I know of no other way of avoiding hand conversion of every module in the library, and hand conversion of every single feature on an existing board. (Hand tweaking the position of 7000 board features is not really an option for me. I do not have access to skilled workers with that low a standard of living.) Do you see the problem? Now that the true position and size of metric things has been destroyed, it might require recreating everthing from scratch. --brian -- Brian F. G. Bidulock � The reasonable man adapts himself to the � [email protected] � world; the unreasonable one persists in � http://www.openss7.org/ � trying to adapt the world to himself. � � Therefore all progress depends on the � � unreasonable man. -- George Bernard Shaw �
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