58 lines
1.9 KiB
ReStructuredText
58 lines
1.9 KiB
ReStructuredText
Supported Features
|
|
==================
|
|
|
|
In addition to the standard architecture devices (HPET, local and I/O APICs,
|
|
etc.), Zephyr supports the following Apollo Lake-specific SoC devices:
|
|
|
|
* HSUART
|
|
|
|
* GPIO
|
|
|
|
* I2C
|
|
|
|
HSUART High-Speed Serial Port Support
|
|
-------------------------------------
|
|
|
|
The Apollo Lake UARTs are NS16550-compatible, with "high-speed" capability.
|
|
|
|
Baud rates beyond 115.2kbps (up to 3.6864Mbps) are supported, with additional
|
|
configuration. The UARTs are fed a master clock which is fed into a PLL which
|
|
in turn outputs the baud master clock. The PLL is controlled by a per-UART
|
|
32-bit register called ``PRV_CLOCK_PARAMS`` (aka the ``PCP``), the format of
|
|
which is:
|
|
|
|
+--------+---------+--------+--------+
|
|
| [31] | [30:16] | [15:1] | [0] |
|
|
+========+=========+========+========+
|
|
| enable | ``m`` | ``n`` | toggle |
|
|
+--------+---------+--------+--------+
|
|
|
|
The resulting baud master clock frequency is ``(n/m)`` * master.
|
|
|
|
Typically, the master clock is 100MHz, and the firmware by default sets
|
|
the ``PCP`` to ``0x3d090240``, i.e., ``n = 288``, ``m = 15625``, which
|
|
results in the de-facto standard 1.8432MHz master clock and a max baud rate
|
|
of 115.2k. Higher baud rates are enabled by changing the PCP and telling
|
|
Zephyr what the resulting master clock is.
|
|
|
|
Use devicetree to set the value of the ``PRV_CLOCK_PARAMS`` register in
|
|
the UART block of interest. Typically an overlay ``up_squared.overlay``
|
|
would be present in the application directory, and would look something
|
|
like this:
|
|
|
|
.. code-block:: console
|
|
|
|
/ {
|
|
soc {
|
|
uart@0 {
|
|
pcp = <0x3d090900>;
|
|
clock-frequency = <7372800>;
|
|
current-speed = <230400>;
|
|
};
|
|
};
|
|
};
|
|
|
|
The relevant variables are ``pcp`` (the value to use for ``PRV_CLOCK_PARAMS``),
|
|
and ``clock-frequency`` (the resulting baud master clock). The meaning of
|
|
``current-speed`` is unchanged, and as usual indicates the initial baud rate.
|