1) make -C editors
This installs a vim syntax file in ~/.vim/syntax/imc.vim
(I have it sym-linked as pasm.vim too).
And:
$cat ~/.vim/ftplugin/imc.vim
augroup filetypedetect
au BufNewFile,BufRead *.imc setf imc
augroup END
$cat ~/.vim/ftplugin/pasm.vim
augroup filetypedetect
au BufNewFile,BufRead *.pasm setf pasm
augroup END
$cat ~/.vim/ftplugin/pmc.vim
augroup filetypedetect
au BufNewFile,BufRead *.pmc setf c
augroup END
2) make tags
While hacking PASM press <ctrl-]> or <g-]> with the cursor standing at an opcode (or some C syntax item of course). This might be helpful, if you don't know all 1384 opcode variants by hard :)
Have fun, leo