| Overview | ||
|---|---|---|
 | Chapter 121. USB Host FTDI Protocol Driver |  |
Name
Overview — eCosPro Support for FTDI Protocol in Host Mode
Description
This package provides protocol support for a host mode connection to FTDI USB to serial adaptors. It needs to be used in conjunction with the USB serial driver package and the reader is referred to that document for additional details.
Usage Model
The eCos serial driver subsystem does not support the dynamic creation and deletion of serial devices. Instead the FTDI driver allocates a number of permanently available serial channels which are allocated to USB devices as they are attached. In order to retain some continuity, it is possible to assign specific Vendor and Product ID values to individual channels so that the USB device will be allocated the same channel each time it is attached.
Writing data to a detached channel will result in that data being lost, just as if it were being written to a disconnected serial line. A detached channel will not produce any data. Changes to the line configuration (baud rate, parity, stop bits, data size, flow control) will be stored and applied to the device once it is attached.
Applications may install a serial line callback function which will
be called with the which field set to
CYGNUM_SERIAL_STATUS_ATTACH and the
value field set to zero for a detach and
one for an attach.
Configuration
To use this package, various other packages need to be included and
configuration options need to be set. The packages that need
to be included are: USB Support (CYGPKG_IO_USB),
USB serial driver (CYGPKG_IO_SERIAL_USB),
Serial device drivers (CYGPKG_IO_SERIAL) and this package
USB host ftdi protocol driver (CYGPKG_IO_USB_FTDI).
Packages can be added directly using ecosconfig add
on the command line, or the Build->Packages…
menu item within the eCos Configuration Tool. Depending on your platform
some of these may already be present in the default eCos configuration.
To activate the requisite USB host and serial support, the options
CYGPKG_IO_USB_HOST
and CYGPKG_IO_SERIAL_DEVICES need to be
enabled. Following this at least one FTDI channel needs to be
configured using the options below.
The configuration option
CYGNUM_IO_USB_FTDI_MAXPKT defines the maximum
packet size used for USB transfers. It is used to define the size of
the the rx_buf in the
usb_serial_if structure. The actual packet
size used by any device is specified in its descriptors. Most
FTDI devices will use a maximum packet size of 64 bytes, and
many will be smaller. So this value should not be reduced unless it
is known that only devices with smaller packet sizes will be used.
The option CYGPKG_IO_USB_FTDI_SUPPORTED_EXTRA
defines an additional set of VID/PID pairs that the driver can
support. A user or HAL package can define this to add entries to
the table of VID/PID pairs that the driver recognizes as valid
devices. This option consists of a comma separated list of
initializers for for a VID/PID structure. For example "{ 0x0403,
0x6001 }, …".
Each serial channel has a number of configuration options associated with it. The following descriptions show the options for serial channel 0, for other channels the zero should be replaced with the number of the channel, currently up to 4.
-
CYGINT_IO_USB_FTDI_SERIAL0 - This interface may be implemented by the platform HAL to instantiate this serial channel.
-
CYGPKG_IO_USB_FTDI_SERIAL0 -
This is the main component that defines this serial channel,
unless this component is enabled, the remaining options will
remain undefined. Its default value is derived from
CYGINT_IO_USB_FTDI_SERIAL0, but it may also be enabled with a requires statement or from the configtool. -
CYGNUM_IO_USB_FTDI_SERIAL0_NAME - This option defines the name of this channel, which eCos applications should use to access the device via cyg_io_lookup(), open() or similar calls. The default is to set it to "/dev/ftdi0" and so on.
-
CYGNUM_IO_USB_FTDI_SERIAL0_BAUD -
This option specifies the default baud rate for this channel. Its
default value is set to
CYGNUM_HAL_VIRTUAL_VECTOR_CONSOLE_CHANNEL_BAUD. -
CYGNUM_IO_USB_FTDI_SERIAL0_BUFSIZE -
This option specifies the size of both the input and output
buffer for the common serial I/O driver layer. This should be at
least equal to
CYGNUM_IO_USB_FTDI_MAXPKTand preferably somewhat larger. The default value makes it twice the maximum packet size. -
CYGNUM_IO_USB_FTDI_SERIAL0_VID - This option controls whether this serial channel matches a particular USB Vendor ID. If zero it will match any ID, otherwise this channel will only match a device with the given vendor ID.
-
CYGNUM_IO_USB_FTDI_SERIAL0_PID This option controls whether this serial channel matches a particular USB Product ID. If zero it will match any ID, otherwise this channel will only match a device with the given product ID.
Channels are searched for a VID and PID match in numerical order, skipping any that are already in use. Therefore lower numbered channels should have more specific VID and PID values and generic channels should be at the end of the list.
-
CYGNUM_IO_USB_FTDI_SERIAL0_LATENCY - This option defines the latency in milliseconds between packets containing data from the FTDI device. If the device has 62 or more bytes available, it will send a packet immediately. Otherwise it will wait this number of milliseconds after the last packet before sending what it has. Decreasing this value will improve responsiveness for low data rate applications at the cost of more activity from the host driver as it processes more packets.
Supported Devices
There is a large family of FTDI devices, some of which support
slightly different variants of the communication protocol. It is
therefore important to detect what kind of device has been
attached. FTDI devices do not have standard class. subclass or
protocol codes defined by the USB-IF. Device descriptors have these
fields set to zero, to redirect them to the interfaces. The
interface fields are set to 0xFF, which is a
reserved vendor specific code. Additionally, FTDI devices can have
internal or external PROMs from which idVendor,
idProduct and string descriptors may be
fetched. The result of all this is that the exact identity of an
FTDI device can be difficult to determine.
The eCosPro FTDI driver employs a number of strategies to determine
whether a device is one that can be supported. The first part of
this is a table of VID/PID pairs. Only if a device can be found in
this table will it be accepted. By default the table contains the
standard FTDI VID/PID values and will be extended to contain the
values for any other devices that have been tested. There is also a
mechanism that allows users or other packages to add entries to
this table using the
CYGPKG_IO_USB_FTDI_SUPPORTED_EXTRA option.
If a device passes the VID/PID test, then other descriptor values
such as bcdDevice
bNumInterface are used to determine which FTDI
device model this is likely to be and adjust the protocol used to
talk to it accordingly.
The eCos FTDI driver has been successfully tested against the following standard FTDI USB serial adapters:
- FTDI CHIPI-X10 (FT231X based)
- FTDI US232R (FT232RL based)
- FTDI US232B (FT232BM based)
In addition an older FT232R and a FT2232C dual channel based devices from manufacturers other than FTDI have also been tested.
| |  | |
| Chapter 121. USB Host FTDI Protocol Driver |  | Part XXXVI. VirtIO Support |
| 2024-03-18 | eCosPro Non-Commercial Public License |