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><A
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><A
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NAME="USBS-DEVTAB">Devtab Entries</H1
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NAME="USBS-DEVTAB">Devtab Entries</H1
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><DIV
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><DIV
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CLASS="REFNAMEDIV"
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CLASS="REFNAMEDIV"
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><A
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><A
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NAME="AEN16237"
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NAME="AEN16237"
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></A
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></A
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><H2
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><H2
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>Name</H2
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>Name</H2
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>Devtab Entries -- Data endpoint data structure</DIV
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>Devtab Entries -- Data endpoint data structure</DIV
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><DIV
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><DIV
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CLASS="REFSYNOPSISDIV"
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CLASS="REFSYNOPSISDIV"
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><A
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><A
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NAME="AEN16240"><H2
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NAME="AEN16240"><H2
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>Synopsis</H2
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>Synopsis</H2
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><TABLE
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><TABLE
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BORDER="5"
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><TR
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><TR
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><TD
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><TD
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><PRE
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><PRE
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CLASS="SYNOPSIS"
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CLASS="SYNOPSIS"
|
>/dev/usb0c
|
>/dev/usb0c
|
/dev/usb1r
|
/dev/usb1r
|
/dev/usb2w</PRE
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/dev/usb2w</PRE
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></TD
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></TD
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></TR
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></TR
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></TABLE
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></TABLE
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></DIV
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></DIV
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><DIV
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><DIV
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CLASS="REFSECT1"
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CLASS="REFSECT1"
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><A
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><A
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NAME="AEN16242"
|
NAME="AEN16242"
|
></A
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></A
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><H2
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><H2
|
>Devtab Entries</H2
|
>Devtab Entries</H2
|
><P
|
><P
|
>USB device drivers provide two ways of transferring data between host
|
>USB device drivers provide two ways of transferring data between host
|
and peripheral. The first involves USB-specific functionality such as
|
and peripheral. The first involves USB-specific functionality such as
|
<A
|
<A
|
HREF="usbs-start-rx.html"
|
HREF="usbs-start-rx.html"
|
><TT
|
><TT
|
CLASS="FUNCTION"
|
CLASS="FUNCTION"
|
>usbs_start_rx_buffer</TT
|
>usbs_start_rx_buffer</TT
|
></A
|
></A
|
>.
|
>.
|
This provides non-blocking I/O: a transfer is started, and some time
|
This provides non-blocking I/O: a transfer is started, and some time
|
later the device driver will call a supplied completion function. The
|
later the device driver will call a supplied completion function. The
|
second uses the conventional I/O model: there are entries in the
|
second uses the conventional I/O model: there are entries in the
|
device table corresponding to the various endpoints. Standard calls
|
device table corresponding to the various endpoints. Standard calls
|
such as <TT
|
such as <TT
|
CLASS="FUNCTION"
|
CLASS="FUNCTION"
|
>open</TT
|
>open</TT
|
> can then be used to get a suitable
|
> can then be used to get a suitable
|
handle. Actual I/O happens via blocking <TT
|
handle. Actual I/O happens via blocking <TT
|
CLASS="FUNCTION"
|
CLASS="FUNCTION"
|
>read</TT
|
>read</TT
|
> and
|
> and
|
<TT
|
<TT
|
CLASS="FUNCTION"
|
CLASS="FUNCTION"
|
>write</TT
|
>write</TT
|
> calls. In practice the blocking operations
|
> calls. In practice the blocking operations
|
are simply implemented using the underlying non-blocking
|
are simply implemented using the underlying non-blocking
|
functionality.</P
|
functionality.</P
|
><P
|
><P
|
>Each endpoint will have its own devtab entry. The exact names are
|
>Each endpoint will have its own devtab entry. The exact names are
|
controlled by the device driver package, but typically the root will
|
controlled by the device driver package, but typically the root will
|
be <TT
|
be <TT
|
CLASS="LITERAL"
|
CLASS="LITERAL"
|
>/dev/usb</TT
|
>/dev/usb</TT
|
>. This is followed by one or more
|
>. This is followed by one or more
|
decimal digits giving the endpoint number, followed by
|
decimal digits giving the endpoint number, followed by
|
<TT
|
<TT
|
CLASS="LITERAL"
|
CLASS="LITERAL"
|
>c</TT
|
>c</TT
|
> for a control endpoint, <TT
|
> for a control endpoint, <TT
|
CLASS="LITERAL"
|
CLASS="LITERAL"
|
>r</TT
|
>r</TT
|
> for
|
> for
|
a receive endpoint (host to peripheral), and <TT
|
a receive endpoint (host to peripheral), and <TT
|
CLASS="LITERAL"
|
CLASS="LITERAL"
|
>w</TT
|
>w</TT
|
> for
|
> for
|
a transmit endpoint (peripheral to host). If the target hardware
|
a transmit endpoint (peripheral to host). If the target hardware
|
involves more than one USB device then different roots should be used,
|
involves more than one USB device then different roots should be used,
|
for example <TT
|
for example <TT
|
CLASS="LITERAL"
|
CLASS="LITERAL"
|
>/dev/usb0c</TT
|
>/dev/usb0c</TT
|
> and
|
> and
|
<TT
|
<TT
|
CLASS="LITERAL"
|
CLASS="LITERAL"
|
>/dev/usb1_0c</TT
|
>/dev/usb1_0c</TT
|
>. This may require explicit
|
>. This may require explicit
|
manipulation of device driver configuration options by the application
|
manipulation of device driver configuration options by the application
|
developer.</P
|
developer.</P
|
><P
|
><P
|
>At present the devtab entry for a control endpoint does not support
|
>At present the devtab entry for a control endpoint does not support
|
any I/O operations. </P
|
any I/O operations. </P
|
><DIV
|
><DIV
|
CLASS="REFSECT2"
|
CLASS="REFSECT2"
|
><A
|
><A
|
NAME="AEN16258"
|
NAME="AEN16258"
|
></A
|
></A
|
><H3
|
><H3
|
><TT
|
><TT
|
CLASS="FUNCTION"
|
CLASS="FUNCTION"
|
>write</TT
|
>write</TT
|
> operations</H3
|
> operations</H3
|
><P
|
><P
|
><TT
|
><TT
|
CLASS="FUNCTION"
|
CLASS="FUNCTION"
|
>cyg_io_write</TT
|
>cyg_io_write</TT
|
> and similar functions in
|
> and similar functions in
|
higher-level packages can be used to perform a transfer from
|
higher-level packages can be used to perform a transfer from
|
peripheral to host. Successive write operations will not be coalesced.
|
peripheral to host. Successive write operations will not be coalesced.
|
For example, when doing a 1000 byte write to an endpoint that uses the
|
For example, when doing a 1000 byte write to an endpoint that uses the
|
bulk transfer protocol this will involve 15 full-size 64-byte packets
|
bulk transfer protocol this will involve 15 full-size 64-byte packets
|
and a terminating 40-byte packet. USB device drivers are not expected
|
and a terminating 40-byte packet. USB device drivers are not expected
|
to do any locking, and if higher-level code performs multiple
|
to do any locking, and if higher-level code performs multiple
|
concurrent write operations on a single endpoint then the resulting
|
concurrent write operations on a single endpoint then the resulting
|
behaviour is undefined.</P
|
behaviour is undefined.</P
|
><P
|
><P
|
>A USB <TT
|
>A USB <TT
|
CLASS="FUNCTION"
|
CLASS="FUNCTION"
|
>write</TT
|
>write</TT
|
> operation will never transfer less
|
> operation will never transfer less
|
data than specified. It is the responsibility of higher-level code to
|
data than specified. It is the responsibility of higher-level code to
|
ensure that the amount of data being transferred is acceptable to the
|
ensure that the amount of data being transferred is acceptable to the
|
host-side code. Usually this will be defined by a higher-level
|
host-side code. Usually this will be defined by a higher-level
|
protocol. If an attempt is made to transfer more data than the host
|
protocol. If an attempt is made to transfer more data than the host
|
expects then the resulting behaviour is undefined.</P
|
expects then the resulting behaviour is undefined.</P
|
><P
|
><P
|
>There are two likely error conditions. <TT
|
>There are two likely error conditions. <TT
|
CLASS="LITERAL"
|
CLASS="LITERAL"
|
>EPIPE</TT
|
>EPIPE</TT
|
>
|
>
|
indicates that the connection between host and target has been broken.
|
indicates that the connection between host and target has been broken.
|
<TT
|
<TT
|
CLASS="LITERAL"
|
CLASS="LITERAL"
|
>EAGAIN</TT
|
>EAGAIN</TT
|
> indicates that the endpoint has been
|
> indicates that the endpoint has been
|
stalled, either at the request of the host or by other activity
|
stalled, either at the request of the host or by other activity
|
inside the peripheral.</P
|
inside the peripheral.</P
|
></DIV
|
></DIV
|
><DIV
|
><DIV
|
CLASS="REFSECT2"
|
CLASS="REFSECT2"
|
><A
|
><A
|
NAME="AEN16268"
|
NAME="AEN16268"
|
></A
|
></A
|
><H3
|
><H3
|
><TT
|
><TT
|
CLASS="FUNCTION"
|
CLASS="FUNCTION"
|
>read</TT
|
>read</TT
|
> operations</H3
|
> operations</H3
|
><P
|
><P
|
><TT
|
><TT
|
CLASS="FUNCTION"
|
CLASS="FUNCTION"
|
>cyg_io_read</TT
|
>cyg_io_read</TT
|
> and similar functions in higher-level
|
> and similar functions in higher-level
|
packages can be used to perform a transfer from host to peripheral.
|
packages can be used to perform a transfer from host to peripheral.
|
This should be a complete transfer: higher-level protocols should
|
This should be a complete transfer: higher-level protocols should
|
define an upper bound on the amount of data being transferred, and the
|
define an upper bound on the amount of data being transferred, and the
|
<TT
|
<TT
|
CLASS="FUNCTION"
|
CLASS="FUNCTION"
|
>read</TT
|
>read</TT
|
> operation should involve at least this
|
> operation should involve at least this
|
amount of data. The return value will indicate the actual transfer
|
amount of data. The return value will indicate the actual transfer
|
size, which may be less than requested.</P
|
size, which may be less than requested.</P
|
><P
|
><P
|
>Some device drivers may support partial reads, but USB device drivers
|
>Some device drivers may support partial reads, but USB device drivers
|
are not expected to perform any buffering because that involves both
|
are not expected to perform any buffering because that involves both
|
memory and code overheads. One technique that may work for bulk
|
memory and code overheads. One technique that may work for bulk
|
transfers is to exploit the fact that such transfers happen in 64-byte
|
transfers is to exploit the fact that such transfers happen in 64-byte
|
packets. It is possible to <TT
|
packets. It is possible to <TT
|
CLASS="FUNCTION"
|
CLASS="FUNCTION"
|
>read</TT
|
>read</TT
|
> an initial 64
|
> an initial 64
|
bytes, corresponding to the first packet in the transfer. These 64
|
bytes, corresponding to the first packet in the transfer. These 64
|
bytes can then be examined to determine the total transfer size, and
|
bytes can then be examined to determine the total transfer size, and
|
the remaining data can be transferred in another
|
the remaining data can be transferred in another
|
<TT
|
<TT
|
CLASS="FUNCTION"
|
CLASS="FUNCTION"
|
>read</TT
|
>read</TT
|
> operation. This technique is not guaranteed
|
> operation. This technique is not guaranteed
|
to work with all USB hardware. Also, if the delay between accepting
|
to work with all USB hardware. Also, if the delay between accepting
|
the first packet and the remainder of the transfer is excessive then
|
the first packet and the remainder of the transfer is excessive then
|
this could cause timeout problems for the host-side software. For
|
this could cause timeout problems for the host-side software. For
|
these reasons the use of partial reads should be avoided.</P
|
these reasons the use of partial reads should be avoided.</P
|
><P
|
><P
|
>There are two likely error conditions. <TT
|
>There are two likely error conditions. <TT
|
CLASS="LITERAL"
|
CLASS="LITERAL"
|
>EPIPE</TT
|
>EPIPE</TT
|
>
|
>
|
indicates that the connection between host and target has been broken.
|
indicates that the connection between host and target has been broken.
|
<TT
|
<TT
|
CLASS="LITERAL"
|
CLASS="LITERAL"
|
>EAGAIN</TT
|
>EAGAIN</TT
|
> indicates that the endpoint has been
|
> indicates that the endpoint has been
|
stalled, either at the request of the host or by other activity
|
stalled, either at the request of the host or by other activity
|
inside the peripheral.</P
|
inside the peripheral.</P
|
><P
|
><P
|
>USB device drivers are not expected to do any locking. If higher-level
|
>USB device drivers are not expected to do any locking. If higher-level
|
code performs multiple concurrent read operations on a single endpoint
|
code performs multiple concurrent read operations on a single endpoint
|
then the resulting behaviour is undefined.</P
|
then the resulting behaviour is undefined.</P
|
></DIV
|
></DIV
|
><DIV
|
><DIV
|
CLASS="REFSECT2"
|
CLASS="REFSECT2"
|
><A
|
><A
|
NAME="AEN16281"
|
NAME="AEN16281"
|
></A
|
></A
|
><H3
|
><H3
|
><TT
|
><TT
|
CLASS="FUNCTION"
|
CLASS="FUNCTION"
|
>select</TT
|
>select</TT
|
> operations</H3
|
> operations</H3
|
><P
|
><P
|
>Typical USB device drivers will not provide any support for
|
>Typical USB device drivers will not provide any support for
|
<TT
|
<TT
|
CLASS="FUNCTION"
|
CLASS="FUNCTION"
|
>select</TT
|
>select</TT
|
>. Consider bulk transfers from the host to
|
>. Consider bulk transfers from the host to
|
the peripheral. At the USB device driver level there is no way of
|
the peripheral. At the USB device driver level there is no way of
|
knowing in advance how large a transfer will be, so it is not feasible
|
knowing in advance how large a transfer will be, so it is not feasible
|
for the device driver to buffer the entire transfer. It may be
|
for the device driver to buffer the entire transfer. It may be
|
possible to buffer part of the transfer, for example the first 64-byte
|
possible to buffer part of the transfer, for example the first 64-byte
|
packet, and copy this into application space at the start of a
|
packet, and copy this into application space at the start of a
|
<TT
|
<TT
|
CLASS="FUNCTION"
|
CLASS="FUNCTION"
|
>read</TT
|
>read</TT
|
>, but this adds code and memory overheads.
|
>, but this adds code and memory overheads.
|
Worse, it means that there is an unknown but potentially long delay
|
Worse, it means that there is an unknown but potentially long delay
|
between a peripheral accepting the first packet of a transfer and the
|
between a peripheral accepting the first packet of a transfer and the
|
remaining packets, which could confuse or upset the host-side
|
remaining packets, which could confuse or upset the host-side
|
software.</P
|
software.</P
|
><P
|
><P
|
>With some USB hardware it may be possible for the device driver to
|
>With some USB hardware it may be possible for the device driver to
|
detect OUT tokens from the host without actually accepting the data,
|
detect OUT tokens from the host without actually accepting the data,
|
and this would indicate that a <TT
|
and this would indicate that a <TT
|
CLASS="FUNCTION"
|
CLASS="FUNCTION"
|
>read</TT
|
>read</TT
|
> is likely to
|
> is likely to
|
succeed. However, it would not be reliable since the host-side I/O
|
succeed. However, it would not be reliable since the host-side I/O
|
operation could time out. A similar mechanism could be used to
|
operation could time out. A similar mechanism could be used to
|
implement <TT
|
implement <TT
|
CLASS="FUNCTION"
|
CLASS="FUNCTION"
|
>select</TT
|
>select</TT
|
> for outgoing data, but again
|
> for outgoing data, but again
|
this would not be reliable.</P
|
this would not be reliable.</P
|
><P
|
><P
|
>Some device drivers may provide partial support for
|
>Some device drivers may provide partial support for
|
<TT
|
<TT
|
CLASS="FUNCTION"
|
CLASS="FUNCTION"
|
>select</TT
|
>select</TT
|
> anyway, possibly under the control of a
|
> anyway, possibly under the control of a
|
configuration option. The device driver's documentation should be
|
configuration option. The device driver's documentation should be
|
consulted for further information. It is also worth noting that the
|
consulted for further information. It is also worth noting that the
|
USB-specific non-blocking API can often be used as an alternative to
|
USB-specific non-blocking API can often be used as an alternative to
|
<TT
|
<TT
|
CLASS="FUNCTION"
|
CLASS="FUNCTION"
|
>select</TT
|
>select</TT
|
>.</P
|
>.</P
|
></DIV
|
></DIV
|
><DIV
|
><DIV
|
CLASS="REFSECT2"
|
CLASS="REFSECT2"
|
><A
|
><A
|
NAME="AEN16293"
|
NAME="AEN16293"
|
></A
|
></A
|
><H3
|
><H3
|
><TT
|
><TT
|
CLASS="FUNCTION"
|
CLASS="FUNCTION"
|
>get_config</TT
|
>get_config</TT
|
> and
|
> and
|
<TT
|
<TT
|
CLASS="FUNCTION"
|
CLASS="FUNCTION"
|
>set_config</TT
|
>set_config</TT
|
> operations</H3
|
> operations</H3
|
><P
|
><P
|
>There are no <TT
|
>There are no <TT
|
CLASS="FUNCTION"
|
CLASS="FUNCTION"
|
>set_config</TT
|
>set_config</TT
|
> or
|
> or
|
<TT
|
<TT
|
CLASS="FUNCTION"
|
CLASS="FUNCTION"
|
>get_config</TT
|
>get_config</TT
|
> (also known as
|
> (also known as
|
<TT
|
<TT
|
CLASS="FUNCTION"
|
CLASS="FUNCTION"
|
>ioctl</TT
|
>ioctl</TT
|
>) operations defined for USB devices.
|
>) operations defined for USB devices.
|
Some device drivers may provide hardware-specific facilities this way. </P
|
Some device drivers may provide hardware-specific facilities this way. </P
|
><DIV
|
><DIV
|
CLASS="NOTE"
|
CLASS="NOTE"
|
><BLOCKQUOTE
|
><BLOCKQUOTE
|
CLASS="NOTE"
|
CLASS="NOTE"
|
><P
|
><P
|
><B
|
><B
|
>Note: </B
|
>Note: </B
|
>Currently the USB-specific functions related to <A
|
>Currently the USB-specific functions related to <A
|
HREF="usbs-halt.html"
|
HREF="usbs-halt.html"
|
>halted endpoints</A
|
>halted endpoints</A
|
> cannot be accessed readily
|
> cannot be accessed readily
|
via devtab entries. This functionality should probably be made
|
via devtab entries. This functionality should probably be made
|
available via <TT
|
available via <TT
|
CLASS="FUNCTION"
|
CLASS="FUNCTION"
|
>set_config</TT
|
>set_config</TT
|
> and
|
> and
|
<TT
|
<TT
|
CLASS="FUNCTION"
|
CLASS="FUNCTION"
|
>get_config</TT
|
>get_config</TT
|
>. It may also prove useful to provide
|
>. It may also prove useful to provide
|
a <TT
|
a <TT
|
CLASS="FUNCTION"
|
CLASS="FUNCTION"
|
>get_config</TT
|
>get_config</TT
|
> operation that maps from the
|
> operation that maps from the
|
devtab entries to the underlying endpoint data structures.</P
|
devtab entries to the underlying endpoint data structures.</P
|
></BLOCKQUOTE
|
></BLOCKQUOTE
|
></DIV
|
></DIV
|
></DIV
|
></DIV
|
><DIV
|
><DIV
|
CLASS="REFSECT2"
|
CLASS="REFSECT2"
|
><A
|
><A
|
NAME="AEN16307"
|
NAME="AEN16307"
|
></A
|
></A
|
><H3
|
><H3
|
>Presence</H3
|
>Presence</H3
|
><P
|
><P
|
>The devtab entries are optional. If the USB device is accessed
|
>The devtab entries are optional. If the USB device is accessed
|
primarily by class-specific code such as the USB-ethernet package and
|
primarily by class-specific code such as the USB-ethernet package and
|
that package uses the USB-specific API directly, the devtab entries
|
that package uses the USB-specific API directly, the devtab entries
|
are redundant. Even if application code does need to access the USB
|
are redundant. Even if application code does need to access the USB
|
device, the non-blocking API may be more convenient than the blocking
|
device, the non-blocking API may be more convenient than the blocking
|
I/O provided via the devtab entries. In these cases the devtab entries
|
I/O provided via the devtab entries. In these cases the devtab entries
|
serve no useful purpose, but they still impose a memory overhead. It
|
serve no useful purpose, but they still impose a memory overhead. It
|
is possible to suppress the presence of these entries by disabling the
|
is possible to suppress the presence of these entries by disabling the
|
configuration option
|
configuration option
|
<TT
|
<TT
|
CLASS="LITERAL"
|
CLASS="LITERAL"
|
>CYGGLO_IO_USB_SLAVE_PROVIDE_DEVTAB_ENTRIES</TT
|
>CYGGLO_IO_USB_SLAVE_PROVIDE_DEVTAB_ENTRIES</TT
|
>.</P
|
>.</P
|
></DIV
|
></DIV
|
></DIV
|
></DIV
|
><DIV
|
><DIV
|
CLASS="NAVFOOTER"
|
CLASS="NAVFOOTER"
|
><HR
|
><HR
|
ALIGN="LEFT"
|
ALIGN="LEFT"
|
WIDTH="100%"><TABLE
|
WIDTH="100%"><TABLE
|
SUMMARY="Footer navigation table"
|
SUMMARY="Footer navigation table"
|
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|
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|
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|
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|
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|
CELLPADDING="0"
|
CELLSPACING="0"
|
CELLSPACING="0"
|
><TR
|
><TR
|
><TD
|
><TD
|
WIDTH="33%"
|
WIDTH="33%"
|
ALIGN="left"
|
ALIGN="left"
|
VALIGN="top"
|
VALIGN="top"
|
><A
|
><A
|
HREF="usbs-start.html"
|
HREF="usbs-start.html"
|
ACCESSKEY="P"
|
ACCESSKEY="P"
|
>Prev</A
|
>Prev</A
|
></TD
|
></TD
|
><TD
|
><TD
|
WIDTH="34%"
|
WIDTH="34%"
|
ALIGN="center"
|
ALIGN="center"
|
VALIGN="top"
|
VALIGN="top"
|
><A
|
><A
|
HREF="ecos-ref.html"
|
HREF="ecos-ref.html"
|
ACCESSKEY="H"
|
ACCESSKEY="H"
|
>Home</A
|
>Home</A
|
></TD
|
></TD
|
><TD
|
><TD
|
WIDTH="33%"
|
WIDTH="33%"
|
ALIGN="right"
|
ALIGN="right"
|
VALIGN="top"
|
VALIGN="top"
|
><A
|
><A
|
HREF="usbs-start-rx.html"
|
HREF="usbs-start-rx.html"
|
ACCESSKEY="N"
|
ACCESSKEY="N"
|
>Next</A
|
>Next</A
|
></TD
|
></TD
|
></TR
|
></TR
|
><TR
|
><TR
|
><TD
|
><TD
|
WIDTH="33%"
|
WIDTH="33%"
|
ALIGN="left"
|
ALIGN="left"
|
VALIGN="top"
|
VALIGN="top"
|
>Starting up a USB Device</TD
|
>Starting up a USB Device</TD
|
><TD
|
><TD
|
WIDTH="34%"
|
WIDTH="34%"
|
ALIGN="center"
|
ALIGN="center"
|
VALIGN="top"
|
VALIGN="top"
|
><A
|
><A
|
HREF="io-usb-slave.html"
|
HREF="io-usb-slave.html"
|
ACCESSKEY="U"
|
ACCESSKEY="U"
|
>Up</A
|
>Up</A
|
></TD
|
></TD
|
><TD
|
><TD
|
WIDTH="33%"
|
WIDTH="33%"
|
ALIGN="right"
|
ALIGN="right"
|
VALIGN="top"
|
VALIGN="top"
|
>Receiving Data from the Host</TD
|
>Receiving Data from the Host</TD
|
></TR
|
></TR
|
></TABLE
|
></TABLE
|
></DIV
|
></DIV
|
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|
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|