libusb performance on 8.1
Greg Troxel
gdt at ir.bbn.com
Tue Feb 22 13:31:26 UTC 2011
While doing some speed testing I find that FreeBSD does ~4Mb/sec, but
Linux does 17Mb/sec & OS X does 8-10Mb/sec.
Check out the bulk read-ahead support in NetBSD's ugen. This was
written at BBN in 2006 to enable higher data rates with the USRP (for
GNU Radio).
From your description it's not clear that this would help, but given
what you're doing you should probably be aware of it.
UGEN(4) NetBSD Kernel Interfaces Manual UGEN(4)
NAME
ugen -- USB generic device support
SYNOPSIS
ugen* at uhub? flags N
options UGEN_BULK_RA_WB
DESCRIPTION
The ugen driver provides support for all USB devices that do not have a
special driver. It supports access to all parts of the device, but not
in a way that is as convenient as a special purpose driver.
Normally the ugen driver is used when no other driver attaches to a
device. If ``flags 1'' is specified, the ugen will instead attach with a
very high priority and always be used. Together with the vendor and
product locators this can be used to force the ugen driver to be used for
a certain device.
There can be up to 127 USB devices connected to a USB bus. Each USB
device can have up to 16 endpoints. Each of these endpoints will commu-
nicate in one of four different modes: control, isochronous, bulk, or
interrupt. Each of the endpoints will have a different device node. The
four least significant bits in the minor device number determines which
endpoint the device accesses and the rest of the bits determines which
USB device.
If an endpoint address is used both for input and output the device can
be opened for both read or write.
To find out what endpoints exist there are a series of ioctl(2) opera-
tions on the control endpoint that return the USB descriptors of the
device, configurations, interfaces, and endpoints.
The control transfer mode can only happen on the control endpoint which
is always endpoint 0. The control endpoint accepts requests and may
respond with an answer to such requests. Control requests are issued by
ioctl(2) calls.
The bulk transfer mode can be in or out depending on the endpoint. To
perform IO on a bulk endpoint read(2) and write(2) should be used. All
IO operations on a bulk endpoint are normally unbuffered. On kernels
built with the UGEN_BULK_RA_WB option, the USB_SET_BULK_RA and
USB_SET_BULK_WB ioctl(2) calls are available, and enable read-ahead and
write-behind buffering respectively. When read-ahead or write-behind are
enabled, the file descriptor may be set to use non-blocking IO.
When in a UGEN_BULK_RA_WB mode, select(2) for read and write operates
normally, returning true if there is data in the read buffer and space in
the write buffer, respectively. When not in a UGEN_BULK_RA_WB mode,
select(2) always returns true, because there is no way to predict how the
device will respond to a read or write request.
The interrupt transfer mode can be in or out depending on the endpoint.
To perform IO on an interrupt endpoint read(2) and write(2) should be
used. A moderate amount of buffering is done by the driver.
All endpoints handle the following ioctl(2) calls:
USB_SET_SHORT_XFER (int)
Allow short read transfer. Normally a transfer from the device
which is shorter than the request specified is reported as an
error.
USB_SET_TIMEOUT (int)
Set the timeout on the device operations, the time is specified
in milliseconds. The value 0 is used to indicate that there is
no timeout.
The control endpoint (endpoint 0) handles the following ioctl(2) calls:
USB_GET_CONFIG (int)
Get the device configuration number.
USB_SET_CONFIG (int)
Set the device into the given configuration number.
This operation can only be performed when the control endpoint is
the sole open endpoint.
USB_GET_ALTINTERFACE (struct usb_alt_interface)
Get the alternative setting number for the interface with the
given index. The config_index is ignored in this call.
struct usb_alt_interface {
int uai_config_index;
int uai_interface_index;
int uai_alt_no;
};
USB_SET_ALTINTERFACE (struct usb_alt_interface)
Set the alternative setting to the given number in the interface
with the given index. The uai_config_index is ignored in this
call.
This operation can only be performed when no endpoints for the
interface are open.
USB_GET_NO_ALT (struct usb_alt_interface)
Return the number of different alternate settings in the
aui_alt_no field.
USB_GET_DEVICE_DESC (usb_device_descriptor_t)
Return the device descriptor.
USB_GET_CONFIG_DESC (struct usb_config_desc)
Return the descriptor for the configuration with the given index.
For convenience the current configuration can be specified by
USB_CURRENT_CONFIG_INDEX.
struct usb_config_desc {
int ucd_config_index;
usb_config_descriptor_t ucd_desc;
};
USB_GET_INTERFACE_DESC (struct usb_interface_desc)
Return the interface descriptor for an interface specified by its
configuration index, interface index, and alternative index. For
convenience the current alternative can be specified by
USB_CURRENT_ALT_INDEX.
struct usb_interface_desc {
int uid_config_index;
int uid_interface_index;
int uid_alt_index;
usb_interface_descriptor_t uid_desc;
};
USB_GET_ENDPOINT_DESC (struct usb_endpoint_desc)
Return the endpoint descriptor for the endpoint specified by its
configuration index, interface index, alternative index, and end-
point index.
struct usb_endpoint_desc {
int ued_config_index;
int ued_interface_index;
int ued_alt_index;
int ued_endpoint_index;
usb_endpoint_descriptor_t ued_desc;
};
USB_GET_FULL_DESC (struct usb_full_desc)
Return all the descriptors for the given configuration.
struct usb_full_desc {
int ufd_config_index;
u_int ufd_size;
u_char *ufd_data;
};
The ufd_data field should point to a memory area of the size
given in the ufd_size field. The proper size can be determined
by first issuing a USB_GET_CONFIG_DESC and inspecting the
wTotalLength field.
USB_GET_STRING_DESC (struct usb_string_desc)
Get a string descriptor for the given language id and string
index.
struct usb_string_desc {
int usd_string_index;
int usd_language_id;
usb_string_descriptor_t usd_desc;
};
USB_DO_REQUEST
Send a USB request to the device on the control endpoint. Any
data sent to/from the device is located at data. The size of the
transferred data is determined from the request. The ucr_addr
field is ignored in this call. The ucr_flags field can be used
to flag that the request is allowed to be shorter than the
requested size, and the ucr_actlen field will contain the actual
size on completion.
struct usb_ctl_request {
int ucr_addr;
usb_device_request_t ucr_request;
void *ucr_data;
int ucr_flags;
#define USBD_SHORT_XFER_OK 0x04 /* allow short reads */
int ucr_actlen; /* actual length transferred */
};
This is a dangerous operation in that it can perform arbitrary
operations on the device. Some of the most dangerous (e.g.,
changing the device address) are not allowed.
USB_GET_DEVICEINFO (struct usb_device_info)
Get an information summary for the device. This call will not
issue any USB transactions.
Bulk endpoints handle the following ioctl(2) calls:
USB_SET_BULK_RA (int)
Enable or disable bulk read-ahead. When enabled, the driver will
begin to read data from the device into a buffer, and will per-
form reads from the device whenever there is room in the buffer.
The read(2) call will read data from this buffer, blocking if
necessary until there is enough data to read the length of data
requested. The buffer size and the read request length can be
set by the USB_SET_BULK_RA_OPT ioctl(2) call.
USB_SET_BULK_WB (int)
Enable or disable bulk write-behind. When enabled, the driver
will buffer data from the write(2) call before writing it to the
device, enabling the write(2) call to return immediately.
write(2) will block if there is not enough room in the buffer for
all the data. The buffer size and the write request length can
be set by the USB_SET_BULK_WB_OPT ioctl(2) call.
USB_SET_BULK_RA_OPT (struct usb_bulk_ra_wb_opt)
Set the size of the buffer and the length of the read requests
used by the driver when bulk read-ahead is enabled. The changes
do not take effect until the next time bulk read-ahead is
enabled. Read requests are made for the length specified, and
the host controller driver (i.e., ehci(4), ohci(4), and uhci(4))
will perform as many bus transfers as required. If transfers
from the device should be smaller than the maximum length,
ra_wb_request_size must be set to the required length.
struct usb_bulk_ra_wb_opt {
u_int ra_wb_buffer_size;
u_int ra_wb_request_size;
};
USB_SET_BULK_WB_OPT (struct usb_bulk_ra_wb_opt)
Set the size of the buffer and the length of the write requests
used by the driver when bulk write-behind is enabled. The
changes do not take effect until the next time bulk write-behind
is enabled.
Note that there are two different ways of addressing configurations,
interfaces, alternatives, and endpoints: by index or by number. The
index is the ordinal number (starting from 0) of the descriptor as pre-
sented by the device. The number is the respective number of the entity
as found in its descriptor. Enumeration of descriptors use the index,
getting and setting typically uses numbers.
Example: All endpoints (except the control endpoint) for the current con-
figuration can be found by iterating the interface_index from 0 to
config_desc->bNumInterface-1 and for each of these iterating the
endpoint_index from 0 to interface_desc->bNumEndpoints. The config_index
should set to USB_CURRENT_CONFIG_INDEX and alt_index should be set to
USB_CURRENT_ALT_INDEX.
FILES
/dev/ugenN.EE Endpoint EE of device N.
SEE ALSO
usb(4)
HISTORY
The ugen driver appeared in NetBSD 1.4.
NetBSD 5.1 January 19, 2008 NetBSD 5.1
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