vhdl-architecture-file-name

vhdl-architecture-file-name is a variable defined in `vhdl-mode.el'.
Its value is

("\\(.*\\) \\(.*\\)" . "\\1_\\2")

Documentation:
Specifies how the architecture file name is obtained.
The architecture file name can be obtained by modifying the entity
and/or architecture name (e.g. attaching or stripping off a substring). The
file extension is automatically taken from the file name of the current
buffer. The string that is matched against the regexp is the concatenation
of the entity and the architecture name separated by a space. This gives
access to both names (see default setting as example).

FROM REGEXP is a regular expression matching the original name:
".*" matches the entire string
"\(...\)" matches a substring
TO STRING specifies the string to be inserted as new name:
"\&" means substitute entire matched text
"\N" means substitute what matched the Nth "\(...\)"
Examples:
".*" "\&" inserts original string
".*" "\&_i" attaches "_i" to original string
"\(.*\)_[io]$" "\1" strips off "_i" or "_o" from original string
".*" "foo" inserts constant string "foo"
".*" "" inserts empty string

You can customize this variable.