I cannot use MIDI with "csound6~".
Warning message is following.

"WARNING: midi disabled (launch with '-+rtmidi=null -M0' to enable)"

I wrote "-+rtmidi=null -M0" in csound csd file. Why?

I use MIDI.pd and midi.csd file.

I use Debian Linux Box.

***** MIDI.pd file
#N canvas 291 164 450 298 10;
#X obj 102 251 dac~;
#X msg 43 53 midi 144 61 100;
#X obj 94 209 csound6~ midi.csd;
#X msg 272 53 midi 144 61 0;
#X text 49 33 push button;
#X text 266 30 release button;
#X connect 1 0 2 0;
#X connect 2 0 0 0;
#X connect 2 1 0 1;
#X connect 3 0 2 0;

****** midi.csd file
<CsoundSynthesizer>
<CsOptions>
-+rtmidi=null -M0
</CsOptions>
<CsInstruments>
instr 1
iFreq cpsmidi ;listen for midi frequency
aout oscil 10000, iFreq, 1
outs aout, aout
endin

</CsInstruments>
<CsScore>
f 1 0 1024 10 1
i1 0 36000
</CsScore>
</CsoundSynthesizer>

Had the same problem (on linux) and just discovered empirically that it works with theses options:
-+rtmidi=linux -M0

You may want to add "--realtime" too, it's a new realtime priority mode that will use all the processors available, says the doc.