m1/patches/rtems: added milkymist-midi-opt.patch

Optimizes MIDI processing.

m1/patches/rtems/milkymist-midi-opt.patch

@@ -0,0 +1,56 @@
+This patch moves MIDI message detection from higher layers to the MIDI
+interrupt handler. This way, MIDI receivers only need to wake up once
+per complete message and not for every single byte.
+
+The /dev/midi queue size is changed from 64 bytes to 32 messages
+(typically 3 bytes each).
+
+Index: rtems/c/src/lib/libbsp/lm32/shared/milkymist_midi/midi.c
+===================================================================
+--- rtems.orig/c/src/lib/libbsp/lm32/shared/milkymist_midi/midi.c	2011-12-01 19:45:37.000000000 -0300
++++ rtems/c/src/lib/libbsp/lm32/shared/milkymist_midi/midi.c	2011-12-02 16:05:30.000000000 -0300
+@@ -26,6 +26,8 @@
+ #define DEVICE_NAME "/dev/midi"
+ 
+ static rtems_id midi_q;
++static unsigned char *midi_p = NULL;
++static unsigned char midi_msg[3];
+ 
+ static rtems_isr interrupt_handler(rtems_vector_number n)
+ {
+@@ -34,7 +36,23 @@
+   while (MM_READ(MM_MIDI_STAT) & MIDI_STAT_RX_EVT) {
+     msg = MM_READ(MM_MIDI_RXTX);
+     MM_WRITE(MM_MIDI_STAT, MIDI_STAT_RX_EVT);
+-    rtems_message_queue_send(midi_q, &msg, 1);
++
++    if ((msg & 0xf8) == 0xf8)
++      continue; /* ignore system real-time */
++
++    if (msg & 0x80)
++      midi_p = midi_msg; /* status byte */
++
++    if (!midi_p)
++      continue; /* ignore extra or unsynchronized data */
++
++    *midi_p++ = msg;
++
++    if (midi_p == midi_msg+3) {
++      /* received a complete MIDI message */
++      rtems_message_queue_send(midi_q, midi_msg, 3);
++      midi_p = NULL;
++    }
+   }
+   lm32_interrupt_ack(1 << MM_IRQ_MIDI);
+ }
+@@ -53,8 +71,8 @@
+ 
+  sc = rtems_message_queue_create(
+     rtems_build_name('M', 'I', 'D', 'I'),
+-    64,
+-    1,
++    32,
++    3,
+     0,
+     &midi_q
+   );

m1/patches/rtems/series

@@ -15,3 +15,4 @@
 # milkymist-videoformat.patch	- applied 2011-11-27
 #fix-timer-includes.patch
 milkymist-usb-midi.patch
+milkymist-midi-opt.patch