📄 adcdev.html
字号:
<!-- Copyright (C) 2009 Free Software Foundation, Inc. -->
<!-- This material may be distributed only subject to the terms -->
<!-- and conditions set forth in the Open Publication License, v1.0 -->
<!-- or later (the latest version is presently available at -->
<!-- http://www.opencontent.org/openpub/). -->
<!-- Distribution of the work or derivative of the work in any -->
<!-- standard (paper) book form is prohibited unless prior -->
<!-- permission is obtained from the copyright holder. -->
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<HTML
><HEAD
><TITLE
>ADC Device Drivers</TITLE
><meta name="MSSmartTagsPreventParsing" content="TRUE">
<META
NAME="GENERATOR"
CONTENT="Modular DocBook HTML Stylesheet Version 1.79"><LINK
REL="HOME"
TITLE="eCos Reference Manual"
HREF="ecos-ref.html"><LINK
REL="UP"
TITLE="ADC Support"
HREF="io-adc.html"><LINK
REL="PREVIOUS"
TITLE="Overview"
HREF="adc.html"><LINK
REL="NEXT"
TITLE="Framebuffer Support"
HREF="io-framebuf.html"></HEAD
><BODY
CLASS="REFENTRY"
BGCOLOR="#FFFFFF"
TEXT="#000000"
LINK="#0000FF"
VLINK="#840084"
ALINK="#0000FF"
><DIV
CLASS="NAVHEADER"
><TABLE
SUMMARY="Header navigation table"
WIDTH="100%"
BORDER="0"
CELLPADDING="0"
CELLSPACING="0"
><TR
><TH
COLSPAN="3"
ALIGN="center"
>eCos Reference Manual</TH
></TR
><TR
><TD
WIDTH="10%"
ALIGN="left"
VALIGN="bottom"
><A
HREF="adc.html"
ACCESSKEY="P"
>Prev</A
></TD
><TD
WIDTH="80%"
ALIGN="center"
VALIGN="bottom"
></TD
><TD
WIDTH="10%"
ALIGN="right"
VALIGN="bottom"
><A
HREF="io-framebuf.html"
ACCESSKEY="N"
>Next</A
></TD
></TR
></TABLE
><HR
ALIGN="LEFT"
WIDTH="100%"></DIV
><H1
><A
NAME="ADCDEV"
></A
>ADC Device Drivers</H1
><DIV
CLASS="REFNAMEDIV"
><A
NAME="AEN9889"
></A
><H2
>Name</H2
>Overview -- ADC Device Drivers</DIV
><DIV
CLASS="REFSECT1"
><A
NAME="ADCDEV-INTRO"
></A
><H2
>Introduction</H2
><P
>This section describes how to write an ADC hardware device. While
users of ADC devices do not need to read it, it may provide added
insight into how the devices work.</P
></DIV
><DIV
CLASS="REFSECT1"
><A
NAME="ADCDEV-DATA"
></A
><H2
>Data Structures</H2
><P
>An ADC hardware driver is represented by a number of data
structures. These are generic <TT
CLASS="LITERAL"
>device</TT
> and
<TT
CLASS="LITERAL"
>channel</TT
> data structures, a driver private device
data structure, a generic character device table entry and a driver
function table. Most of these structures are instantiated using
macros, which will be described here.</P
><P
>The data structure instantiation for a typical single device, four
channel ADC would look like this:</P
><TABLE
BORDER="5"
BGCOLOR="#E0E0F0"
WIDTH="70%"
><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
>//==========================================================================
// Instantiate data structures
// -------------------------------------------------------------------------
// Driver functions:
CYG_ADC_FUNCTIONS( example_adc_funs,
example_adc_enable,
example_adc_disable,
example_adc_set_rate );
// -------------------------------------------------------------------------
// Device instance:
static example_adc_info example_adc_info0 =
{
.base = CYGARC_HAL_EXAMPLE_ADC_BASE,
.vector = CYGNUM_HAL_INTERRUPT_ADC
};
CYG_ADC_DEVICE( example_adc_device,
&example_adc_funs,
&example_adc_info0,
CYGNUM_IO_ADC_EXAMPLE_DEFAULT_RATE );
// -------------------------------------------------------------------------
// Channel instances:
#define EXAMPLE_ADC_CHANNEL( __chan ) \
CYG_ADC_CHANNEL( example_adc_channel##__chan, \
__chan, \
CYGNUM_IO_ADC_EXAMPLE_CHANNEL##__chan##_BUFSIZE, \
&example_adc_device ); \
\
DEVTAB_ENTRY( example_adc_channel##__chan##_device, \
CYGDAT_IO_ADC_EXAMPLE_CHANNEL##__chan##_NAME, \
0, \
&cyg_io_adc_devio, \
example_adc_init, \
example_adc_lookup, \
&example_adc_channel##__chan );
EXAMPLE_ADC_CHANNEL( 0 );
EXAMPLE_ADC_CHANNEL( 1 );
EXAMPLE_ADC_CHANNEL( 2 );
EXAMPLE_ADC_CHANNEL( 3 );</PRE
></TD
></TR
></TABLE
><P
>The macro <TT
CLASS="LITERAL"
>CYG_ADC_FUNCTIONS()</TT
> instantiates a
function table called <CODE
CLASS="VARNAME"
>example_adc_funs</CODE
> and
populates it with the ADC driver functions (see later for details).</P
><P
>Then an instance of the driver private device data structure is
instantiated. In addition to the device base address and interrupt
vector shown here, this stucture should contain the interrupt object
and handle for attaching to the vector. It may also contain any other
variables needed to manage the device.</P
><P
>The macro <TT
CLASS="LITERAL"
>CYG_ADC_DEVICE()</TT
> instantiates a
<CODE
CLASS="STRUCTNAME"
>cyg_adc_device</CODE
> structure, named
<CODE
CLASS="VARNAME"
>example_adc_device</CODE
> which will contain pointers to
the function table and private data structure. The initial sample rate
is also supplied here.</P
><P
>For each channel, an ADC channel structure and a device table entry
must be created. The macro <TT
CLASS="LITERAL"
>EXAMPLE_ADC_CHANNEL()</TT
> is
defined to simplify this process. The macro
<TT
CLASS="LITERAL"
>CYG_ADC_CHANNEL</TT
> defines a
<CODE
CLASS="STRUCTNAME"
>cyg_adc_channel</CODE
> structure, which contains the
channel number, the buffer size, and a pointer to the device object
defined earlier. The call to <TT
CLASS="LITERAL"
>DEVTAB_ENTRY()</TT
>
generates a device table entry containing the configured channel name,
a pointer to a device function table defined in the generic ADC
driver, pointers to init and lookup functions implemented here, and a
pointer to the channel data structure just defined.</P
><P
>Finally, four channels, numbered 0 to 3 are created.</P
></DIV
><DIV
CLASS="REFSECT1"
><A
NAME="ADCDEV-FUNCTIONS"
></A
><H2
>Functions</H2
><P
>There are several classes of function that need to be defined in an
ADC driver. These are those function that go into the channel's device
table, those that go into the ADC device's function table, calls that
the driver makes into the generic ADC package, and interrupt handling
functions.</P
><DIV
CLASS="REFSECT2"
><A
NAME="ADCDEV-FUNCTIONS-DEVTAB"
></A
><H3
>Device Table Functions</H3
><P
>These functions are placed in the standard device table entry for each
channel and handle initialization and location of the device within
the generic driver infrastructure.</P
><P
><CODE
CLASS="FUNCTION"
>static bool example_adc_init(struct cyg_devtab_entry *tab)</CODE
>
This function is called from the device IO infrastructure to
initialize the device. It should perform any work needed to start up
the device, short of actually starting the generation of samples. This
function will be called for each channel, so if there is
initialization that only needs to be done once, such as creating an
interrupt object, then care should be taken to do this. This function
should also call <CODE
CLASS="FUNCTION"
>cyg_adc_device_init()</CODE
> to
initialize the generic parts of the driver.</P
><P
><CODE
CLASS="FUNCTION"
>static Cyg_ErrNo example_adc_lookup(struct cyg_devtab_entry **tab, struct cyg_devtab_entry *sub_tab, const char *name)</CODE
>
This function is called when a client looks up or opens a channel. It
should call <CODE
CLASS="FUNCTION"
>cyg_adc_channel_init()</CODE
> to initialize
the generic part of the channel. It should also perform any operations
needed to start the channel generating samples.</P
></DIV
><DIV
CLASS="REFSECT2"
><A
NAME="ADCDEV-FUNCTIONS-DRIVER"
></A
><H3
>Driver Functions</H3
><P
>These are the functions installed into the driver function table by
the <TT
CLASS="LITERAL"
>CYG_ADC_FUNCTIONS()</TT
> macro.</P
><P
><CODE
CLASS="FUNCTION"
>static void example_adc_enable( cyg_adc_channel *chan )</CODE
>
This function is called from the generic ADC package to enable the
channel in response to a
<TT
CLASS="LITERAL"
>CYG_IO_SET_CONFIG_ADC_ENABLE</TT
> config operation. It
should take any steps needed to start the channel generating samples.</P
><P
><CODE
CLASS="FUNCTION"
>static void example_adc_disable( cyg_adc_channel *chan )</CODE
>
This function is called from the generic ADC package to enable the
channel in response to a
<TT
CLASS="LITERAL"
>CYG_IO_SET_CONFIG_ADC_DISABLE</TT
> config operation. It
should take any steps needed to stop the channel generating samples.</P
><P
><CODE
CLASS="FUNCTION"
>static void example_adc_set_rate( cyg_adc_channel *chan, cyg_uint32 rate )</CODE
>
This function is called from the generic ADC package to enable the
channel in response to a <TT
CLASS="LITERAL"
>CYG_IO_SET_CONFIG_ADC_RATE</TT
>
config operation. It should take any steps needed to change the sample
rate of the channel, or of the entire device.</P
></DIV
><DIV
CLASS="REFSECT2"
><A
NAME="ADCDEV-FUNCTIONS-GENERIC"
></A
><H3
>Generic Package Functions</H3
><P
>These functions are called by a hardware ADC device driver to perform
operations in the generic ADC package.</P
><P
><CODE
CLASS="FUNCTION"
>__externC void cyg_adc_device_init( cyg_adc_device *device )</CODE
>
This function is called from the driver's init function and is used to
initialize the <SPAN
CLASS="TYPE"
>cyg_adc_device</SPAN
> object.</P
><P
><CODE
CLASS="FUNCTION"
>__externC void cyg_adc_channel_init(cyg_adc_channel *chan)</CODE
>
This function is called from the driver's lookup function and is used
to initialize the <SPAN
CLASS="TYPE"
>cyg_adc_channel</SPAN
> object.</P
><P
><CODE
CLASS="FUNCTION"
>__externC cyg_uint32 cyg_adc_receive_sample(cyg_adc_channel *chan, cyg_adc_sample_t sample)</CODE
>
This function is called from the driver's ISR to add a new sample to
the buffer. The return value will be either zero, or
<TT
CLASS="LITERAL"
>CYG_ISR_CALL_DSR</TT
> and should be ORed with the return
value of the ISR.</P
><P
><CODE
CLASS="FUNCTION"
>__externC void cyg_adc_wakeup(cyg_adc_channel *chan )</CODE
>
This function is called from the driver's DSR to cause any threads
waiting for data to wake up when a new sample is available. It should
only be called if the <CODE
CLASS="STRUCTFIELD"
>wakeup</CODE
> field of the
channel object is <TT
CLASS="LITERAL"
>true</TT
>.</P
></DIV
><DIV
CLASS="REFSECT2"
><A
NAME="ADCDEV-FUNCTIONS-INTERRUPT"
></A
><H3
>Interrupt Functions</H3
><P
>These functions are internal to the driver, but make calls on generic
package functions. Typically an ADC device will have a single
interrupt vector with which it signals available samples on the
channels and any error conditions such as overruns.</P
><P
><CODE
CLASS="FUNCTION"
>static cyg_uint32 example_adc_isr(cyg_vector_t vector, cyg_addrword_t data)</CODE
>
This function is the ISR attached to the ADC device's interrupt
vector. It is responsible for reading samples from the channels and
passing them on to the generic layer. It needs to check each channel
for data, and call <CODE
CLASS="FUNCTION"
>cyg_adc_receive_sample()</CODE
> for
each new sample available, and then ready the device for the next
interrupt. It's activities are best explained by example:</P
><TABLE
BORDER="5"
BGCOLOR="#E0E0F0"
WIDTH="70%"
><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
>static cyg_uint32 example_adc_isr(cyg_vector_t vector, cyg_addrword_t data)
{
cyg_adc_device *example_device = (cyg_adc_device *) data;
example_adc_info *example_info = example_device->dev_priv;
cyg_uint32 res = 0;
int i;
// Deal with errors if necessary
DEVICE_CHECK_ERRORS( example_info );
// Look for all channels with data available
for( i = 0; i < CHANNEL_COUNT; i++ )
{
if( CHANNEL_SAMPLE_AVALIABLE(i) )
{
// Fetch data from this channel and pass up to higher
// level.
cyg_adc_sample_t data = CHANNEL_GET_SAMPLE(i);
res |= CYG_ISR_HANDLED | cyg_adc_receive_sample( example_info->channel[i], data );
}
}
// Clear any interrupt conditions
DEVICE_CLEAR_INTERRUPTS( example_info );
cyg_drv_interrupt_acknowledge(example_info->vector);
return res;
}</PRE
></TD
></TR
></TABLE
><P
><CODE
CLASS="FUNCTION"
>static void example_adc_dsr(cyg_vector_t vector, cyg_ucount32 count, cyg_addrword_t data)</CODE
>
This function is the DSR attached to the ADC device's interrupt
vector. It is called by the kernel if the ISR return value contains
the <TT
CLASS="LITERAL"
>CYG_ISR_HANDLED</TT
> bit. It needs to call
<CODE
CLASS="FUNCTION"
>cyg_adc_wakeup()</CODE
> for each channel that has its
<CODE
CLASS="STRUCTFIELD"
>wakeup</CODE
> field set. Again, and example should
make it all clear:</P
><TABLE
BORDER="5"
BGCOLOR="#E0E0F0"
WIDTH="70%"
><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
>static void example_adc_dsr(cyg_vector_t vector, cyg_ucount32 count, cyg_addrword_t data)
{
cyg_adc_device *example_device = (cyg_adc_device *) data;
example_adc_info *example_info = example_device->dev_priv;
int i;
// Look for all channels with pending wakeups
for( i = 0; i < CHANNEL_COUNT; i++ )
{
if( example_info->channel[i]->wakeup )
cyg_adc_wakeup( example_info->channel[i] );
}
} </PRE
></TD
></TR
></TABLE
></DIV
></DIV
><DIV
CLASS="NAVFOOTER"
><HR
ALIGN="LEFT"
WIDTH="100%"><TABLE
SUMMARY="Footer navigation table"
WIDTH="100%"
BORDER="0"
CELLPADDING="0"
CELLSPACING="0"
><TR
><TD
WIDTH="33%"
ALIGN="left"
VALIGN="top"
><A
HREF="adc.html"
ACCESSKEY="P"
>Prev</A
></TD
><TD
WIDTH="34%"
ALIGN="center"
VALIGN="top"
><A
HREF="ecos-ref.html"
ACCESSKEY="H"
>Home</A
></TD
><TD
WIDTH="33%"
ALIGN="right"
VALIGN="top"
><A
HREF="io-framebuf.html"
ACCESSKEY="N"
>Next</A
></TD
></TR
><TR
><TD
WIDTH="33%"
ALIGN="left"
VALIGN="top"
>Overview</TD
><TD
WIDTH="34%"
ALIGN="center"
VALIGN="top"
><A
HREF="io-adc.html"
ACCESSKEY="U"
>Up</A
></TD
><TD
WIDTH="33%"
ALIGN="right"
VALIGN="top"
>Framebuffer Support</TD
></TR
></TABLE
></DIV
></BODY
></HTML
>⌨️ 快捷键说明
复制代码
Ctrl + C
搜索代码
Ctrl + F
全屏模式
F11
切换主题
Ctrl + Shift + D
显示快捷键
?
增大字号
Ctrl + =
减小字号
Ctrl + -