[vhdl-200x] What is Minimal Risk?

From: Jim Lewis <jim@synthworks.com>
Date: Tue Apr 28 2015 - 08:46:30 PDT
Hi All,
Martin raised an interesting issue, what is "minimal risk".   Any comments?

 From my perspective, one big issue is that we don't accidentally break old code.
For example, in VHDL-2008, the standard packages now includes the function:
function "+"(L: unsigned, R: std_ulogic) return unsigned ;

Unfortunately this means that old code of the form will result in an error since
& and + have equal precedence and evaluate left to right:
signal A, B : unsigned (7 downto 0) ;
signal Y : unsigned(8 downto 0) ;
Y <= '0' & A + '0' & B ;

With parentheses added the code is fine:
Y <= '0' & A + ('0' & B) ;

Since most tools allow specification of a compile switch, so this issue is not challenging to work around.

Best Regards,

Jim Lewis                                  Jim@SynthWorks.com
VHDL Training Expert                       http://www.SynthWorks.com
IEEE VHDL Working Group Chair
OSVVM, Chief Architect and Cofounder

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Received on Tue Apr 28 08:47:17 2015

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