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<html xmlns="http://www.w3.org/1999/xhtml"><head><meta http-equiv="Content-Type" content="text/html; charset=ANSI_X3.4-1968" /><title>Constructor</title><meta name="generator" content="DocBook XSL Stylesheets V1.75.2" /><link rel="home" href="index.html" title="Writing an ALSA Driver" /><link rel="up" href="ch08.html" title="Chapter 8. MIDI (MPU401-UART) Interface" /><link rel="prev" href="ch08.html" title="Chapter 8. MIDI (MPU401-UART) Interface" /><link rel="next" href="ch08s03.html" title="Interrupt Handler" /></head><body><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="3" align="center">Constructor</th></tr><tr><td width="20%" align="left"><a accesskey="p" href="ch08.html">Prev</a> </td><th width="60%" align="center">Chapter 8. MIDI (MPU401-UART) Interface</th><td width="20%" align="right"> <a accesskey="n" href="ch08s03.html">Next</a></td></tr></table><hr /></div><div class="section" title="Constructor"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a id="midi-interface-constructor"></a>Constructor</h2></div></div></div><p>
To create a rawmidi object, call
<code class="function">snd_mpu401_uart_new()</code>.
</p><div class="informalexample"><pre class="programlisting">
struct snd_rawmidi *rmidi;
snd_mpu401_uart_new(card, 0, MPU401_HW_MPU401, port, info_flags,
irq, irq_flags, &rmidi);
</pre></div><p>
</p><p>
The first argument is the card pointer, and the second is the
index of this component. You can create up to 8 rawmidi
devices.
</p><p>
The third argument is the type of the hardware,
<code class="constant">MPU401_HW_XXX</code>. If it's not a special one,
you can use <code class="constant">MPU401_HW_MPU401</code>.
</p><p>
The 4th argument is the I/O port address. Many
backward-compatible MPU401 have an I/O port such as 0x330. Or, it
might be a part of its own PCI I/O region. It depends on the
chip design.
</p><p>
The 5th argument is a bitflag for additional information.
When the I/O port address above is part of the PCI I/O
region, the MPU401 I/O port might have been already allocated
(reserved) by the driver itself. In such a case, pass a bit flag
<code class="constant">MPU401_INFO_INTEGRATED</code>,
and the mpu401-uart layer will allocate the I/O ports by itself.
</p><p>
When the controller supports only the input or output MIDI stream,
pass the <code class="constant">MPU401_INFO_INPUT</code> or
<code class="constant">MPU401_INFO_OUTPUT</code> bitflag, respectively.
Then the rawmidi instance is created as a single stream.
</p><p>
<code class="constant">MPU401_INFO_MMIO</code> bitflag is used to change
the access method to MMIO (via readb and writeb) instead of
iob and outb. In this case, you have to pass the iomapped address
to <code class="function">snd_mpu401_uart_new()</code>.
</p><p>
When <code class="constant">MPU401_INFO_TX_IRQ</code> is set, the output
stream isn't checked in the default interrupt handler. The driver
needs to call <code class="function">snd_mpu401_uart_interrupt_tx()</code>
by itself to start processing the output stream in the irq handler.
</p><p>
Usually, the port address corresponds to the command port and
port + 1 corresponds to the data port. If not, you may change
the <em class="structfield"><code>cport</code></em> field of
struct <span class="structname">snd_mpu401</span> manually
afterward. However, <span class="structname">snd_mpu401</span> pointer is not
returned explicitly by
<code class="function">snd_mpu401_uart_new()</code>. You need to cast
rmidi->private_data to
<span class="structname">snd_mpu401</span> explicitly,
</p><div class="informalexample"><pre class="programlisting">
struct snd_mpu401 *mpu;
mpu = rmidi->private_data;
</pre></div><p>
and reset the cport as you like:
</p><div class="informalexample"><pre class="programlisting">
mpu->cport = my_own_control_port;
</pre></div><p>
</p><p>
The 6th argument specifies the irq number for UART. If the irq
is already allocated, pass 0 to the 7th argument
(<em class="parameter"><code>irq_flags</code></em>). Otherwise, pass the flags
for irq allocation
(<code class="constant">SA_XXX</code> bits) to it, and the irq will be
reserved by the mpu401-uart layer. If the card doesn't generate
UART interrupts, pass -1 as the irq number. Then a timer
interrupt will be invoked for polling.
</p></div><div class="navfooter"><hr /><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="ch08.html">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="ch08.html">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="ch08s03.html">Next</a></td></tr><tr><td width="40%" align="left" valign="top">Chapter 8. MIDI (MPU401-UART) Interface </td><td width="20%" align="center"><a accesskey="h" href="index.html">Home</a></td><td width="40%" align="right" valign="top"> Interrupt Handler</td></tr></table></div></body></html>
