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freebsd-dev/sys/dev/usb/README.TXT
Andrew Thompson 02ac645488 Move the new USB stack into its new home.
2009-02-23 18:31:00 +00:00

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$FreeBSD$
DESCRIPTION OF THE NEW USB API
The new USB 2.0 API consists of 5 functions. All transfer types are
managed using these functions. There is no longer need for separate
functions to setup INTERRUPT- and ISOCHRONOUS- transfers.
+--------------------------------------------------------------+
| |
| "usb2_transfer_setup" - This function will allocate all |
| necessary DMA memory and might |
| sleep! |
| |
| "usb2_transfer_unsetup" - This function will stop the USB |
| transfer, if it is currently |
| active, release all DMA |
| memory and might sleep! |
| |
| "usb2_transfer_start" - This function will start an USB |
| transfer, if not already started.|
| This function is always |
| non-blocking. ** |
| |
| "usb2_transfer_stop" - This function will stop an USB |
| transfer, if not already stopped.|
| The callback function will be |
| called before this function |
| returns. This function is always |
| non-blocking. ** |
| |
| "usb2_transfer_drain" - This function will stop an USB |
| transfer, if not already stopped |
| and wait for any additional |
| DMA load operations to complete. |
| Buffers that are loaded into DMA |
| using "usb2_set_frame_data" can |
| safely be freed after that |
| this function has returned. This |
| function can block the caller. |
| |
| ** These functions must be called with the private driver's |
| lock locked. |
| |
| NOTE: These USB API functions are NULL safe, with regard |
| to the USB transfer structure pointer. |
+--------------------------------------------------------------+
Reference: /sys/dev/usb/usb_transfer.c
/*
* A simple USB callback state-machine:
*
* +->-----------------------+
* | |
* +-<-+-------[tr_setup]--------+-<-+-<-[start/restart]
* | |
* | |
* | |
* +------>-[tr_transferred]---------+
* | |
* +--------->-[tr_error]------------+
*/
void
usb2_default_callback(struct usb2_xfer *xfer)
{
/*
* NOTE: it is not allowed to return
* before "USB_CHECK_STATUS()",
* even if the system is tearing down!
*/
switch (USB_GET_STATE(xfer)) {
case USB_ST_SETUP:
/*
* Setup xfer->frlengths[], xfer->nframes
* and write data to xfer->frbuffers[], if any
*/
/**/
usb2_start_hardware(xfer);
return;
case USB_ST_TRANSFERRED:
/*
* Read data from xfer->frbuffers[], if any.
* "xfer->frlengths[]" should now have been
* updated to the actual length.
*/
return;
default: /* Error */
/* print error message and clear stall for example */
return;
}
}
=== Notes for USB control transfers ===
An USB control transfer has three parts. First the SETUP packet, then
DATA packet(s) and then a STATUS packet. The SETUP packet is always
pointed to by "xfer->frbuffers[0]" and the length is stored in
"xfer->frlengths[0]" also if there should not be sent any SETUP
packet! If an USB control transfer has no DATA stage, then
"xfer->nframes" should be set to 1. Else the default value is
"xfer->nframes" equal to 2.
Example1: SETUP + STATUS
xfer->nframes = 1;
xfer->frlenghts[0] = 8;
usb2_start_hardware(xfer);
Example2: SETUP + DATA + STATUS
xfer->nframes = 2;
xfer->frlenghts[0] = 8;
xfer->frlenghts[1] = 1;
usb2_start_hardware(xfer);
Example3: SETUP + DATA + STATUS - split
1st callback:
xfer->nframes = 1;
xfer->frlenghts[0] = 8;
usb2_start_hardware(xfer);
2nd callback:
/* IMPORTANT: frbuffer[0] must still point at the setup packet! */
xfer->nframes = 2;
xfer->frlenghts[0] = 0;
xfer->frlenghts[1] = 1;
usb2_start_hardware(xfer);
Example4: SETUP + STATUS - split
1st callback:
xfer->nframes = 1;
xfer->frlenghts[0] = 8;
xfer->flags.manual_status = 1;
usb2_start_hardware(xfer);
2nd callback:
xfer->nframes = 1;
xfer->frlenghts[0] = 0;
xfer->flags.manual_status = 0;
usb2_start_hardware(xfer);
=== General USB transfer notes ===
1) Something that one should be aware of is that all USB callbacks support
recursation. That means one can start/stop whatever transfer from the callback
of another transfer one desires. Also the transfer that is currently called
back. Recursion is handled like this that when the callback that wants to
recurse returns it is called one more time.
2) After that the "usb2_start_hardware()" function has been called in
the callback one can always depend on that "tr_error" or "tr_transferred"
will get jumped afterwards. Always!
3) Sleeping functions can only be called from the attach routine of the
driver. Else one should not use sleeping functions unless one has to. It is
very difficult with sleep, because one has to think that the device might have
detached when the thread returns from sleep.
4) Polling.
use_polling
This flag can be used with any callback and will cause the
"usb2_transfer_start()" function to wait using "DELAY()",
without exiting any mutexes, until the transfer is finished or
has timed out. This flag can be changed during operation.
NOTE: If polling is used the "timeout" field should be non-zero!
NOTE: USB_ERR_CANCELLED is returned in case of timeout
instead of USB_ERR_TIMEOUT!
USB device driver examples:
/sys/dev/usb/net/if_axe.c
/sys/dev/usb/net/if_aue.c
QUICK REFERENCE
===============
/*------------------------------------------------------------------------*
* usb2_error_t
* usb2_transfer_setup(udev, ifaces, pxfer, setup_start,
* n_setup, priv_sc, priv_mtx)
*------------------------------------------------------------------------*/
- "udev" is a pointer to "struct usb2_device".
- "ifaces" array of interface index numbers to use. See "if_index".
- "pxfer" is a pointer to an array of USB transfer pointers that are
initialized to NULL, and then pointed to allocated USB transfers.
- "setup_start" is a pointer to an array of USB config structures.
- "n_setup" is a number telling the USB system how many USB transfers
should be setup.
- "priv_sc" is the private softc pointer, which will be used to
initialize "xfer->priv_sc".
- "priv_mtx" is the private mutex protecting the transfer structure and
the softc. This pointer is used to initialize "xfer->priv_mtx".
/*------------------------------------------------------------------------*
* void
* usb2_transfer_unsetup(pxfer, n_setup)
*------------------------------------------------------------------------*/
- "pxfer" is a pointer to an array of USB transfer pointers, that may
be NULL, that should be freed by the USB system.
- "n_setup" is a number telling the USB system how many USB transfers
should be unsetup
NOTE: This function can sleep, waiting for active mutexes to become unlocked!
NOTE: It is not allowed to call "usb2_transfer_unsetup" from the callback
of a USB transfer.
/*------------------------------------------------------------------------*
* void
* usb2_transfer_start(xfer)
*------------------------------------------------------------------------*/
- "xfer" is pointer to a USB transfer that should be started
NOTE: this function must be called with "priv_mtx" locked
/*------------------------------------------------------------------------*
* void
* usb2_transfer_stop(xfer)
*------------------------------------------------------------------------*/
- "xfer" is a pointer to a USB transfer that should be stopped
NOTE: this function must be called with "priv_mtx" locked
NOTE: if the transfer was in progress, the callback will called with
"xfer->error=USB_ERR_CANCELLED", before this function returns
/*------------------------------------------------------------------------*
* struct usb2_config {
* type, endpoint, direction, interval, timeout, frames, index
* flags, bufsize, callback
* };
*------------------------------------------------------------------------*/
- The "type" field selects the USB pipe type. Valid values are:
UE_INTERRUPT, UE_CONTROL, UE_BULK, UE_ISOCHRONOUS. The special
value UE_BULK_INTR will select BULK and INTERRUPT pipes.
This field is mandatory.
- The "endpoint" field selects the USB endpoint number. A value of
0xFF, "-1" or "UE_ADDR_ANY" will select the first matching endpoint.
This field is mandatory.
- The "direction" field selects the USB endpoint direction. A value of
"UE_DIR_ANY" will select the first matching endpoint. Else valid
values are: "UE_DIR_IN" and "UE_DIR_OUT". "UE_DIR_IN" and
"UE_DIR_OUT" can be binary ORed by "UE_DIR_SID" which means that the
direction will be swapped in case of USB_MODE_DEVICE. Note that
"UE_DIR_IN" refers to the data transfer direction of the "IN" tokens
and "UE_DIR_OUT" refers to the data transfer direction of the "OUT"
tokens. This field is mandatory.
- The "interval" field selects the interrupt interval. The value of this
field is given in milliseconds and is independent of device speed. Depending
on the endpoint type, this field has different meaning:
UE_INTERRUPT)
"0" use the default interrupt interval based on endpoint descriptor.
"Else" use the given value for polling rate.
UE_ISOCHRONOUS)
"0" use default.
"Else" the value is ignored.
UE_BULK)
UE_CONTROL)
"0" no transfer pre-delay.
"Else" a delay as given by this field in milliseconds is
inserted before the hardware is started when
"usb2_start_hardware()" is called.
NOTE: The transfer timeout, if any, is started after that
the pre-delay has elapsed!
- The "timeout" field, if non-zero, will set the transfer timeout in
milliseconds. If the "timeout" field is zero and the transfer type
is ISOCHRONOUS a timeout of 250ms will be used.
- The "frames" field sets the maximum number of frames. If zero is
specified it will yield the following results:
UE_BULK)
UE_INTERRUPT)
xfer->nframes = 1;
UE_CONTROL)
xfer->nframes = 2;
UE_ISOCHRONOUS)
Not allowed. Will cause an error.
- The "ep_index" field allows you to give a number, in case more
endpoints match the description, that selects which matching
"ep_index" should be used.
- The "if_index" field allows you to select which of the interface
numbers in the "ifaces" array parameter passed to "usb2_transfer_setup"
that should be used when setting up the given USB transfer.
- The "flags" field has type "struct usb2_xfer_flags" and allows one
to set initial flags an USB transfer. Valid flags are:
force_short_xfer
This flag forces the last transmitted USB packet to be short.
A short packet has a length of less than "xfer->max_packet_size",
which derives from "wMaxPacketSize". This flag can be changed
during operation.
short_xfer_ok
This flag allows the received transfer length, "xfer->actlen"
to be less than "xfer->sumlen" upon completion of a transfer.
This flag can be changed during operation.
pipe_bof
This flag causes a failing USB transfer to remain first
in the PIPE queue except in the case of "xfer->error" equal
to "USB_ERR_CANCELLED". No other USB transfers in the affected
PIPE queue will be started until either:
1) The failing USB transfer is stopped using "usb2_transfer_stop()".
2) The failing USB transfer performs a successful transfer.
The purpose of this flag is to avoid races when multiple
transfers are queued for execution on an USB endpoint, and the
first executing transfer fails leading to the need for
clearing of stall for example. In this case this flag is used
to prevent the following USB transfers from being executed at
the same time the clear-stall command is executed on the USB
control endpoint. This flag can be changed during operation.
"BOF" is short for "Block On Failure"
NOTE: This flag should be set on all BULK and INTERRUPT
USB transfers which use an endpoint that can be shared
between userland and kernel.
proxy_buffer
Setting this flag will cause that the total buffer size will
be rounded up to the nearest atomic hardware transfer
size. The maximum data length of any USB transfer is always
stored in the "xfer->max_data_length". For control transfers
the USB kernel will allocate additional space for the 8-bytes
of SETUP header. These 8-bytes are not counted by the
"xfer->max_data_length" variable. This flag can not be changed
during operation.
ext_buffer
Setting this flag will cause that no data buffer will be
allocated. Instead the USB client must supply a data buffer.
This flag can not be changed during operation.
manual_status
Setting this flag prevents an USB STATUS stage to be appended
to the end of the USB control transfer. If no control data is
transferred this flag must be cleared. Else an error will be
returned to the USB callback. This flag is mostly useful for
the USB device side. This flag can be changed during
operation.
no_pipe_ok
Setting this flag causes the USB_ERR_NO_PIPE error to be
ignored. This flag can not be changed during operation.
stall_pipe
Setting this flag will cause STALL pids to be sent to the
endpoint belonging to this transfer before the transfer is
started. The transfer is started at the moment the host issues
a clear-stall command on the STALL'ed endpoint. This flag can
be changed during operation. This flag does only have effect
in USB device side mode except for control endpoints. This
flag is cleared when the stall command has been executed. This
flag can only be changed outside the callback function by
using the functions "usb2_transfer_set_stall()" and
"usb2_transfer_clear_stall()" !
- The "bufsize" field sets the total buffer size in bytes. If
this field is zero, "wMaxPacketSize" will be used, multiplied by the
"frames" field if the transfer type is ISOCHRONOUS. This is useful for
setting up interrupt pipes. This field is mandatory.
NOTE: For control transfers "bufsize" includes
the length of the request structure.
- The "callback" pointer sets the USB callback. This field is mandatory.
MUTEX NOTE:
===========
When you create a mutex using "mtx_init()", don't forget to call
"mtx_destroy()" at detach, else you can get "freed memory accessed"
panics.
--HPS
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