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The new i2c driver in the beagle BSP uses FDT based initialization. This updates the documentation of the BSP about the same.
243 lines
8.1 KiB
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243 lines
8.1 KiB
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.. SPDX-License-Identifier: CC-BY-SA-4.0
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.. Copyright (C) 2019 Vijay Kumar Banerjee
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.. _BSP_arm_beagle:
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.. _BSP_arm_beagleboardorig:
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.. _BSP_arm_beagleboardxm:
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.. _BSP_arm_beagleboneblack:
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.. _BSP_arm_beaglebonewhite:
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beagle
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======
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This BSP supports four variants, `beagleboardorig`, `beagleboardxm`,
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`beaglebonewhite` and `beagleboneblack`. The basic hardware initialization is
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not performed by the BSP. A boot loader with device tree support must be used
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to start the BSP, e.g., U-Boot.
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TODO(These drivers are present but not documented yet):
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* Clock driver.
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* Network Interface Driver.
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* SDcard driver.
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* GPIO Driver.
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* Console driver.
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* PWM Driver.
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* RTC driver.
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Boot via U-Boot
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---------------
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To boot via uboot, the ELF must be converted to a U-Boot image like below:
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.. code-block:: none
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arm-rtems5-objcopy hello.exe -O binary app.bin
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gzip -9 app.bin
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mkimage -A arm -O linux -T kernel -a 0x80000000 -e 0x80000000 -n RTEMS -d app.bin.gz rtems-app.img
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Getting the Device Tree Blob
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----------------------------
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The Device Tree Blob (DTB) is needed to load the device tree while starting up
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the kernel. We build the dtb from the FreeBSD source matching the commit hash
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from the libbsd HEAD of freebsd-org. For example if the HEAD is at
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"19a6ceb89dbacf74697d493e48c388767126d418"
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Then the right Device Tree Source (DTS) file is:
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https://github.com/freebsd/freebsd/blob/19a6ceb89dbacf74697d493e48c388767126d418/sys/gnu/dts/arm/am335x-boneblack.dts
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Please refer to the :ref:`DeviceTree` to know more about building and applying
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the Device Trees.
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Writing the uEnv.txt file
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-------------------------
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The uEnv.txt file is needed to set any environment variable before the kernel is
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loaded. Each line is a u-boot command that the uboot will execute during start
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up.
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Add the following to a file named uEnv.txt:
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.. code-block:: none
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setenv bootdelay 5
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uenvcmd=run boot
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boot=fatload mmc 0 0x80800000 rtems-app.img ; fatload mmc 0 0x88000000 am335x-boneblack.dtb ; bootm 0x80800000 - 0x88000000
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I2C Driver
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----------
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The Beagle i2c initialization is based on the device tree. To initialize a i2c
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device, the user has to enable the respective node in the device tree using
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overlays.
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For registering an I2C device with a custom path (say `/dev/i2c-eeprom`) an
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overlay has to be provided. The overlay must add an additional attribute
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`rtems,path` with the custom path as value to the respective i2c node.
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For example,
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.. code-block::
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/dts-v1/;
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/ {
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compatible = "ti,am335x-bone-black", "ti,am335x-bone", "ti,am33xx";
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fragment@0 {
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target = <0xffffffff>;
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__overlay__ {
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compatible = "rtems,bsp-i2c", "ti,omap4-i2c";
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status = "okay";
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rtems,path = "/dev/i2c-eeprom";
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};
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};
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__fixups__ {
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i2c0 = "/fragment@0:target:0";
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};
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};
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The above example registers a custom path `/dev/i2c-eeprom` for i2c0.
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SPI Driver
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----------
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The SPI device `/dev/spi-0` can be registered with ``bbb_register_spi_0()``
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For registering with a custom path, the ``bsp_register_spi()`` can be used.
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The function prototype is given below:
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.. code-block:: C
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rtems_status_code bsp_register_spi(
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const char *bus_path,
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uintptr_t register_base,
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rtems_vector_number irq
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);
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Debugging using libdebugger
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---------------------------
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RTEMS's ``libdebugger`` requires the ARM debug resources be enabled for it to
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work. The TI SOC used on the ``beagleboneblack`` board provides no access for
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software to the ARM defined debug enable signal ``DBGEN``. The signal is
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negated on power up locking software out of the ARM debug hardware. The signal
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can only be accessed via the JTAG interface.
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The ``beagleboneblack`` BSP provides a low level solution to enable the
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``DBGEN`` signal via the JTAG interface if the board has the following
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hardware modification installed. The modification requires the addition of two
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small wire links soldered to the pads of the JTAG connect on the underside of
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the board. A small length of fine wire, a fine tip soldering iron, some good
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quality solder and a pair of fine tip pliers are required. If you are new to
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soldering I suggest you find something to practice on first.
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The modification details and software driver can be found in the BSP in the
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file ``bsps/arm/beagle/start/bspdebug.c``. The driver is automatically run
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and the ``DBGEN`` is asserted via JTAG when ``libdebugger`` is started.
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The modification is:
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1. Locate P2 on the bottom side of the board. It is the JTAG connector
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pads. If you look at the underside of the board with the SD card holder to
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the right the pads are top center left. There are 20 pads in two
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columns. The pads are numbered 1 at the top left then 2 top right, 3 is
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second top on the left, 4 is second top to the right, then the pin number
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increments as you move left then right down the pads.
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2. Connect P2 to P5.
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3. Connect P7 to P13.
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The resulting wiring is:
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.. code-block::
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1 === /--=== 2
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3 === | === 4
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5 ===--/ === 6
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7 ===--\ === 8
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9 === | === 10
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11 === | === 12
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13 ===--/ === 14
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15 === === 16
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17 === === 18
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19 === === 20
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.. figure:: ../../images/user/bbb-p2-debug-mod.jpg
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:width: 50%
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:align: center
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:alt: BeagleBone Black JTAG Hardware Modification
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BeagleBone Black JTAG Hardware Modification
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If ``libdebugger`` fails to detect the registers open the ``bspdebug.c``
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source and change ``has_tdo`` to ``1``, save then rebuild and install the
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BSP. This will turn on an internal feeback to check the JTAG logic. Discard
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the edit once the hardware is working.
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Debugging Beagle Bone Black using a JTAG debugger and gdb
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---------------------------------------------------------
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Debugging a Beagle Bone Black (or variants) is also possible using a hardware
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JTAG debugger. The JTAG is available via P2. The footprint is for an ARM 20 pin
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cTI connector. That connector should be used, if it is necessary to have access
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to commercially available adapters.
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For hand-made cables and adapters a standard 1.27mm pitch header and a 0.635mm
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ribbon cable can be much cheaper. But note that even if it looks compatible,
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it's not the same pin out as a ARM Cortex 20 pin connector!
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A lot of JTAG adapters that are working together with OpenOCD will work. There
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are also commercially available systems (like Segger J-Link) that work well with
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the Beagle. Note that the JTAG debugger has to be compatible with ARM Cortex A8.
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Cortex M only debuggers (like the Segger J-Link Edu Mini) won't work.
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If the debugger offers a gdb server (like OpenOCD or Segger J-Link) the
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following gdb start script can be used:
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.. code-block::
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define reset
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echo -- Reset target and wait for U-Boot to start kernel.\n
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monitor reset
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# RTEMS U-Boot starts at this address.
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tbreak *0x80000000
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# Linux starts here.
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tbreak *0x82000000
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continue
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echo -- Disable watchdog.\n
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set *(uint32_t*)0x44e35048=0xAAAA
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while (*(uint32_t*)0x44e35034 != 0)
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end
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set *(uint32_t*)0x44e35048=0x5555
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while (*(uint32_t*)0x44e35034 != 0)
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end
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echo -- Overwrite kernel with application to debug.\n
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load
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end
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target remote :2331
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Note that you might have to replace the ``monitor reset`` by some other command
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that resets the target using your specific debugger. You also have to replace
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the ``target remote :2331`` to match the port of your gdb server.
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The script expects that the Beagle Bone Black starts some application from an SD
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card or from eMMC. It defines a ``reset`` command that does the following:
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* reset the target
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* let U-Boot run, initialize the base system, load an FDT and an application
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* break at the application entry point
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* disable the watchdog
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* overwrite the application that has been loaded by U-Boot with the application
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provided as an command line argument to gdb
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This method has the advantage that the application is executed in nearly the
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same environment like it would be executed if loaded by U-Boot directly (except
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for the watchdog).
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