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The XR21B1421, XR21B1422 and XR21B1424 are the one-, two- and four-port models of a second XR21B142X type of the Maxlinear/Exar USB UARTs. The XR21B142X type differs from XR21V141X in several ways, including: - register layout - register width (16-bit instead of 8-bit) - vendor register requests - UART enable/disable sequence - custom-driver mode flag - three additional GPIOs (9 instead of 6) As for XR21V141X, the XR21B142X vendor requests encode the channel index in the MSB of wIndex, but it lacks the UART Manager registers which have been replaced by regular UART registers. The new type also uses the interface number of the control interface (0, 2, 4, 6) as channel index instead of the channel number (0, 1, 2, 3). The XR21B142X lacks the divisor and format registers used by XR21V141X and instead uses the CDC SET_LINE_CONTROL request to configure the line settings. Note that the currently supported XR21V141X type lacks the custom-driver mode flag that prevents the device from entering CDC-ACM mode when a CDC requests is received. This specifically means that the SET_LINE_CONTROL request cannot be used with XR21V141X even though it is otherwise supported. The UART enable sequence for XR21B142X does not involve explicitly enabling the FIFOs, but according to datasheet the UART must be disabled when writing any register but GPIO_SET, GPIO_CLEAR, TX_BREAK and ERROR_STATUS. Signed-off-by: Johan Hovold <johan@kernel.org> |
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Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.