user: Add ARM BSPs chapter

Add NXP i.MX section as a BSP example.

Update #2854.

user/bsps/bsps-arm.rst

@@ -0,0 +1,138 @@
+.. comment SPDX-License-Identifier: CC-BY-SA-4.0
+.. comment Copyright (c) 2017, 2018 embedded brains GmbH
+
+arm (ARM)
+*********
+
+NXP i.MX
+========
+
+This BSP offers only one variant, the `imx7`.  This variant supports the i.MX
+7Dual processor.  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.
+
+Build Configuration Options
+---------------------------
+
+The following options are available at the configure command line.
+
+``BSP_PRESS_KEY_FOR_RESET``
+    If defined to a non-zero value, then print a message and wait until pressed
+    before resetting board when application terminates.
+
+``BSP_RESET_BOARD_AT_EXIT``
+    If defined to a non-zero value, then reset the board when the application
+    terminates.
+
+``BSP_PRINT_EXCEPTION_CONTEXT``
+    If defined to a non-zero value, then print the exception context when an
+    unexpected exception occurs.
+
+``BSP_FDT_BLOB_SIZE_MAX``
+    The maximum size of the device tree blob in bytes (default is 262144).
+
+``CONSOLE_USE_INTERRUPTS``
+    Use interrupt driven mode for console devices (enabled by default).
+
+``IMX_CCM_IPG_HZ``
+   The IPG clock frequency in Hz (default is 67500000).
+
+``IMX_CCM_UART_HZ``
+   The UART clock frequency in Hz (default is 24000000).
+
+``IMX_CCM_AHB_HZ``
+   The AHB clock frequency in Hz (default is 135000000).
+
+Boot via U-Boot
+---------------
+
+The application executable file (ELF file) must be converted to an U-Boot
+image.  Use the following commands:
+
+::
+
+    arm-rtems5-objcopy -O binary app.exe app.bin
+    gzip -9 -f -c app.bin > app.bin.gz
+    mkimage -A arm -O linux -T kernel -a 0x80200000 -e 0x80200000 -n RTEMS -d app.bin.gz app.img
+
+Use the following U-Boot commands to boot an application via TFTP download:
+
+::
+
+    tftpboot ${loadaddr} app.img && run loadfdt && bootm ${loadaddr} - ${fdt_addr} ; reset
+
+Clock Driver
+------------
+
+The clock driver uses the `ARMv7-AR Generic Timer`.
+
+Console Driver
+--------------
+
+The console driver supports up to seven on-chip UARTs.  They are initialized
+according to the device tree.  The console driver does not configure the pins.
+
+I2C Driver
+----------
+
+I2C drivers are registered by the ``i2c_bus_register_imx()`` function.  The I2C
+driver does not configure the pins.
+
+.. code-block:: c
+
+    #include <assert.h>
+    #include <bsp.h>
+
+    void i2c_init(void)
+    {
+      int rv;
+
+      rv = i2c_bus_register_imx("/dev/i2c-0", "i2c0");
+      assert(rv == 0);
+    }
+
+SPI Driver
+----------
+
+SPI drivers are registered by the ``spi_bus_register_imx()`` function.  The SPI
+driver configures the pins according to the ``pinctrl-0`` device tree property.
+SPI transfers with a continuous chip select are limited by the FIFO size of 64
+bytes.  The driver has no DMA support.
+
+.. code-block:: c
+
+    #include <assert.h>
+    #include <bsp.h>
+
+    void spi_init(void)
+    {
+      int rv;
+
+      rv =  spi_bus_register_imx("/dev/spi-0", "spi0");
+      assert(rv == 0);
+    }
+
+Network Interface Driver
+------------------------
+
+The network interface driver is provided by the `libbsd`.  It is initialized
+according to the device tree.  It supports checksum offload and interrupt
+coalescing.  IPv6 transmit checksum offload is not implemented.  The interrupt
+coalescing uses the MII/GMII clocks and can be controlled by the following
+system controls:
+
+ * ``dev.ffec.<unit>.int_coal.rx_time``
+ * ``dev.ffec.<unit>.int_coal.rx_count``
+ * ``dev.ffec.<unit>.int_coal.tx_time``
+ * ``dev.ffec.<unit>.int_coal.tx_count``
+
+A value of zero for the time or count disables the interrupt coalescing in the
+corresponding direction.
+
+Caveats
+-------
+
+The clock and pin configuration support is quite rudimentary and mostly relies
+on the boot loader.  For a pin group configuration see
+``imx_iomux_configure_pins()``.  There is no power management support.

user/bsps/index.rst

@@ -0,0 +1,14 @@
+.. comment SPDX-License-Identifier: CC-BY-SA-4.0
+
+.. comment: Copyright (c) 2018 embedded brains GmbH
+.. comment: All rights reserved.
+
+.. _BoardSupportPackages:
+
+Board Support Packages (BSPs)
+*****************************
+.. index:: Board Support Packages (BSPs)
+
+.. toctree::
+
+   bsps-arm

user/index.rst

@@ -49,6 +49,7 @@ to the Community Project hosted at http://www.rtems.org/.
 	installation/index
 
 	hardware/index
+	bsps/index
 
 	tools/index