+<!-- ****************************************************** -->
+<!-- RawMIDI Interface -->
+<!-- ****************************************************** -->
+ <chapter id="rawmidi-interface">
+ <title>RawMIDI Interface</title>
+
+ <section id="rawmidi-interface-overview">
+ <title>Overview</title>
+
+ <para>
+ The raw MIDI interface is used for hardware MIDI ports that can
+ be accessed as a byte stream. It is not used for synthesizer
+ chips that do not directly understand MIDI.
+ </para>
+
+ <para>
+ ALSA handles file and buffer management. All you have to do is
+ to write some code to move data between the buffer and the
+ hardware.
+ </para>
+
+ <para>
+ The rawmidi API is defined in
+ <filename><sound/rawmidi.h></filename>.
+ </para>
+ </section>
+
+ <section id="rawmidi-interface-constructor">
+ <title>Constructor</title>
+
+ <para>
+ To create a rawmidi device, call the
+ <function>snd_rawmidi_new</function> function:
+ <informalexample>
+ <programlisting>
+<![CDATA[
+ struct snd_rawmidi *rmidi;
+ err = snd_rawmidi_new(chip->card, "MyMIDI", 0, outs, ins, &rmidi);
+ if (err < 0)
+ return err;
+ rmidi->private_data = chip;
+ strcpy(rmidi->name, "My MIDI");
+ rmidi->info_flags = SNDRV_RAWMIDI_INFO_OUTPUT |
+ SNDRV_RAWMIDI_INFO_INPUT |
+ SNDRV_RAWMIDI_INFO_DUPLEX;
+]]>
+ </programlisting>
+ </informalexample>
+ </para>
+
+ <para>
+ The first argument is the card pointer, the second argument is
+ the ID string.
+ </para>
+
+ <para>
+ The third argument is the index of this component. You can
+ create up to 8 rawmidi devices.
+ </para>
+
+ <para>
+ The fourth and fifth arguments are the number of output and
+ input substreams, respectively, of this device. (A substream is
+ the equivalent of a MIDI port.)
+ </para>
+
+ <para>
+ Set the <structfield>info_flags</structfield> field to specify
+ the capabilities of the device.
+ Set <constant>SNDRV_RAWMIDI_INFO_OUTPUT</constant> if there is
+ at least one output port,
+ <constant>SNDRV_RAWMIDI_INFO_INPUT</constant> if there is at
+ least one input port,
+ and <constant>SNDRV_RAWMIDI_INFO_DUPLEX</constant> if the device
+ can handle output and input at the same time.
+ </para>
+
+ <para>
+ After the rawmidi device is created, you need to set the
+ operators (callbacks) for each substream. There are helper
+ functions to set the operators for all substream of a device:
+ <informalexample>
+ <programlisting>
+<![CDATA[
+ snd_rawmidi_set_ops(rmidi, SNDRV_RAWMIDI_STREAM_OUTPUT, &snd_mymidi_output_ops);
+ snd_rawmidi_set_ops(rmidi, SNDRV_RAWMIDI_STREAM_INPUT, &snd_mymidi_input_ops);
+]]>
+ </programlisting>
+ </informalexample>
+ </para>
+
+ <para>
+ The operators are usually defined like this:
+ <informalexample>
+ <programlisting>
+<![CDATA[
+ static struct snd_rawmidi_ops snd_mymidi_output_ops = {
+ .open = snd_mymidi_output_open,
+ .close = snd_mymidi_output_close,
+ .trigger = snd_mymidi_output_trigger,
+ };
+]]>
+ </programlisting>
+ </informalexample>
+ These callbacks are explained in the <link
+ linkend="rawmidi-interface-callbacks"><citetitle>Callbacks</citetitle></link>
+ section.
+ </para>
+
+ <para>
+ If there is more than one substream, you should give each one a
+ unique name:
+ <informalexample>
+ <programlisting>
+<![CDATA[
+ struct list_head *list;
+ struct snd_rawmidi_substream *substream;
+ list_for_each(list, &rmidi->streams[SNDRV_RAWMIDI_STREAM_OUTPUT].substreams) {
+ substream = list_entry(list, struct snd_rawmidi_substream, list);
+ sprintf(substream->name, "My MIDI Port %d", substream->number + 1);
+ }
+ /* same for SNDRV_RAWMIDI_STREAM_INPUT */
+]]>
+ </programlisting>
+ </informalexample>
+ </para>
+ </section>
+
+ <section id="rawmidi-interface-callbacks">
+ <title>Callbacks</title>
+
+ <para>
+ In all callbacks, the private data that you've set for the
+ rawmidi device can be accessed as
+ substream->rmidi->private_data.
+ <!-- <code> isn't available before DocBook 4.3 -->
+ </para>
+
+ <para>
+ If there is more than one port, your callbacks can determine the
+ port index from the struct snd_rawmidi_substream data passed to each
+ callback:
+ <informalexample>
+ <programlisting>
+<![CDATA[
+ struct snd_rawmidi_substream *substream;
+ int index = substream->number;
+]]>
+ </programlisting>
+ </informalexample>
+ </para>
+
+ <section id="rawmidi-interface-op-open">
+ <title><function>open</function> callback</title>
+
+ <informalexample>
+ <programlisting>
+<![CDATA[
+ static int snd_xxx_open(struct snd_rawmidi_substream *substream);
+]]>
+ </programlisting>
+ </informalexample>
+
+ <para>
+ This is called when a substream is opened.
+ You can initialize the hardware here, but you should not yet
+ start transmitting/receiving data.
+ </para>
+ </section>
+
+ <section id="rawmidi-interface-op-close">
+ <title><function>close</function> callback</title>
+
+ <informalexample>
+ <programlisting>
+<![CDATA[
+ static int snd_xxx_close(struct snd_rawmidi_substream *substream);
+]]>
+ </programlisting>
+ </informalexample>
+
+ <para>
+ Guess what.
+ </para>
+
+ <para>
+ The <function>open</function> and <function>close</function>
+ callbacks of a rawmidi device are serialized with a mutex,
+ and can sleep.
+ </para>
+ </section>
+
+ <section id="rawmidi-interface-op-trigger-out">
+ <title><function>trigger</function> callback for output
+ substreams</title>
+
+ <informalexample>
+ <programlisting>
+<![CDATA[
+ static void snd_xxx_output_trigger(struct snd_rawmidi_substream *substream, int up);
+]]>
+ </programlisting>
+ </informalexample>
+
+ <para>
+ This is called with a nonzero <parameter>up</parameter>
+ parameter when there is some data in the substream buffer that
+ must be transmitted.
+ </para>
+
+ <para>
+ To read data from the buffer, call
+ <function>snd_rawmidi_transmit_peek</function>. It will
+ return the number of bytes that have been read; this will be
+ less than the number of bytes requested when there is no more
+ data in the buffer.
+ After the data has been transmitted successfully, call
+ <function>snd_rawmidi_transmit_ack</function> to remove the
+ data from the substream buffer:
+ <informalexample>
+ <programlisting>
+<![CDATA[
+ unsigned char data;
+ while (snd_rawmidi_transmit_peek(substream, &data, 1) == 1) {
+ if (snd_mychip_try_to_transmit(data))
+ snd_rawmidi_transmit_ack(substream, 1);
+ else
+ break; /* hardware FIFO full */
+ }
+]]>
+ </programlisting>
+ </informalexample>
+ </para>
+
+ <para>
+ If you know beforehand that the hardware will accept data, you
+ can use the <function>snd_rawmidi_transmit</function> function
+ which reads some data and removes it from the buffer at once:
+ <informalexample>
+ <programlisting>
+<![CDATA[
+ while (snd_mychip_transmit_possible()) {
+ unsigned char data;
+ if (snd_rawmidi_transmit(substream, &data, 1) != 1)
+ break; /* no more data */
+ snd_mychip_transmit(data);
+ }
+]]>
+ </programlisting>
+ </informalexample>
+ </para>
+
+ <para>
+ If you know beforehand how many bytes you can accept, you can
+ use a buffer size greater than one with the
+ <function>snd_rawmidi_transmit*</function> functions.
+ </para>
+
+ <para>
+ The <function>trigger</function> callback must not sleep. If
+ the hardware FIFO is full before the substream buffer has been
+ emptied, you have to continue transmitting data later, either
+ in an interrupt handler, or with a timer if the hardware
+ doesn't have a MIDI transmit interrupt.
+ </para>
+
+ <para>
+ The <function>trigger</function> callback is called with a
+ zero <parameter>up</parameter> parameter when the transmission
+ of data should be aborted.
+ </para>
+ </section>
+
+ <section id="rawmidi-interface-op-trigger-in">
+ <title><function>trigger</function> callback for input
+ substreams</title>
+
+ <informalexample>
+ <programlisting>
+<![CDATA[
+ static void snd_xxx_input_trigger(struct snd_rawmidi_substream *substream, int up);
+]]>
+ </programlisting>
+ </informalexample>
+
+ <para>
+ This is called with a nonzero <parameter>up</parameter>
+ parameter to enable receiving data, or with a zero
+ <parameter>up</parameter> parameter do disable receiving data.
+ </para>
+
+ <para>
+ The <function>trigger</function> callback must not sleep; the
+ actual reading of data from the device is usually done in an
+ interrupt handler.
+ </para>
+
+ <para>
+ When data reception is enabled, your interrupt handler should
+ call <function>snd_rawmidi_receive</function> for all received
+ data:
+ <informalexample>
+ <programlisting>
+<![CDATA[
+ void snd_mychip_midi_interrupt(...)
+ {
+ while (mychip_midi_available()) {
+ unsigned char data;
+ data = mychip_midi_read();
+ snd_rawmidi_receive(substream, &data, 1);
+ }
+ }
+]]>
+ </programlisting>
+ </informalexample>
+ </para>
+ </section>
+
+ <section id="rawmidi-interface-op-drain">
+ <title><function>drain</function> callback</title>
+
+ <informalexample>
+ <programlisting>
+<![CDATA[
+ static void snd_xxx_drain(struct snd_rawmidi_substream *substream);
+]]>
+ </programlisting>
+ </informalexample>
+
+ <para>
+ This is only used with output substreams. This function should wait
+ until all data read from the substream buffer has been transmitted.
+ This ensures that the device can be closed and the driver unloaded
+ without losing data.
+ </para>
+
+ <para>
+ This callback is optional. If you do not set
+ <structfield>drain</structfield> in the struct snd_rawmidi_ops
+ structure, ALSA will simply wait for 50 milliseconds
+ instead.
+ </para>
+ </section>
+ </section>
+
+ </chapter>
+
+