[PATCH] user/bsps : Add documentation for Beagle

[Vijay Kumar Banerjee]

---
 user/bsps/arm/beagle.rst | 91 +++++++++++++++++++++++++++++++++++++++-
 1 file changed, 89 insertions(+), 2 deletions(-)

diff --git a/user/bsps/arm/beagle.rst b/user/bsps/arm/beagle.rst
index a36efde..84bfe2d 100644
--- a/user/bsps/arm/beagle.rst
+++ b/user/bsps/arm/beagle.rst
@@ -1,8 +1,95 @@
 .. SPDX-License-Identifier: CC-BY-SA-4.0
 
-.. Copyright (C) 2019 TBD
+.. Copyright (C) 2019 Vijay Kumar Banerjee
 
 beagle
 ======
 
-TODO.
+This BSP supports four variants, `beagleboardorig`, `beagleboardxm`, `beaglebonewhite`
+and `beagleboneblack`. The basic hardware initialization is not performed by
+the BSP.  A boot loader with device tree support must be used to start the BSP,
+e.g. U-Boot.
+
+TODO(These drivers are present but not documented yet):
+
+ *  Clock driver.
+ *  Network Interface Driver.
+ *  SDcard driver.
+ *  GPIO Driver.
+ *  Console driver.
+ *  PWM Driver.
+ *  RTC driver.
+
+Boot via U-Boot
+---------------
+To boot via uboot, the ELF must be converted to a U-Boot image like below:
+
+.. code-block:: none
+
+    arm-rtems5-objcopy hello.exe -O app.bin
+    gzip 9 app.bin
+    mkimage -A arm -O linux -T kernel -a 0x80000000 -e 0x80000000 -n RTEMS -d app.bin.gz rtems-app.img
+
+Getting the Device Tree Blob
+----------------------------
+
+The Device Tree Blob(dtb) is needed to load the device tree while starting up
+the kernel. We build the dtb from the FreeBSD source matching the commit hash
+from the libbsd HEAD of freebsd-org. For example if the HEAD is at
+"19a6ceb89dbacf74697d493e48c388767126d418"
+Then the right dts file is:
+https://github.com/freebsd/freebsd/blob/19a6ceb89dbacf74697d493e48c388767126d418/sys/gnu/dts/arm/am335x-boneblack.dts
+
+.. code-block:: none
+
+     #building the dtb
+     #We will use the script from https://github.com/freebsd/freebsd/blob/19a6ceb89dbacf74697d493e48c388767126d418/sys/tools/fdt/make_dtb.sh
+
+     export MACHINE='arm' #The make_dtb.sh script uses environment variable MACHINE
+     SCRIPT_DIR=$HOME/freebsd/sys/tools/fdt
+     #The arguments to the script are
+     # $1 -> Build Tree
+     # $2 -> DTS source file
+     # $3 -> output path of the DTB file
+     ${SCRIPT_DIR}/make_dtb.sh ${SCRIPT_DIR}/../../ \
+     ${SCRIPT_DIR}/../../gnu/dts/arm/am335x-boneblack.dts \
+     $(pwd)
+Writing the uEnv.txt file
+-------------------------
+
+The uEnv.txt file is needed to set any environment variable before the kernel is
+loaded. Each line is a u-boot command that the uboot will execute during
+starting up.
+
+Add the following to a file named uEnv.txt:
+
+.. code-block:: none
+
+     setenv bootdelay 5
+     uenvcmd=run boot
+     boot=fatload mmc 0 0x80800000 rtems-app.img ; fatload mmc 0 0x88000000 am335x-boneblack.dtb ; bootm 0x80800000 - 0x88000000
+
+I2C Driver
+----------
+
+This BSP uses the I2C framework and is registered using
+``am335x_i2c_bus_register()`` the function prototype is given below:
+
+.. code-block:: C
+
+   int am335x_i2c_bus_register(
+   const char         *bus_path,
+   uintptr_t           register_base,
+   uint32_t            input_clock,
+   rtems_vector_number irq
+   );
+
+This function is needed only while registering with custom path with custom
+values. For registering the `/dev/i2c-0` device, a wrapper function is provided,
+``bbb_register_i2c_0()`` similarly ``bbb_register_i2c_1()`` and
+``bbb_register_i2c_2()`` are respectively used to register `i2c-1` and `i2c-2`.
+
+SPI Driver
+----------
+
+The SPI device `/dev/spi-0` can be registered with ``bbb_register_spi_0()```
-- 
2.20.1