8.2.14. raspberrypi#

The ‘raspberrypi’ BSP supports the single core models (Zero, Zero W, A+, B+), and the ‘raspberrypi2’ BSP supports the Raspberry Pi 2, Raspberry Pi 3 A+, and Raspberry Pi 3. The Raspberry Pi 4 is supported by the AArch64 Raspberry Pi BSP. The default bootloader on the Raspberry Pi which is used to boot Raspbian or other OS can be also used to boot RTEMS. U-boot can also be used.

8.2.14.1. Setup SD card#

The Raspberry Pis have an unconventional booting mechanism. The GPU boots first, initializes itself, runs the bootloader and starts the CPU. The bootloader looks for a kernel image, by default the kernel images must have a name of the form kernel*.img but this can be changed by adding kernel=<img_name> to config.txt.

You must provide the required firmware files on the SD card for the GPU to proceed, and thereby to boot RTEMS. The BSP currently boots up with an older version of the official firmware. These files can be downloaded from the Raspberry Pi Firmware Repository. You can remove the kernel*.img files if you want to, but don’t touch the other files.

Copy these files in to a SD card with FAT filesystem.

8.2.14.2. Kernel image#

The following steps show how to run hello.exe on a Raspberry Pi 2. The same instructions can be applied to Raspberry Pi 1 also. Other executables can be processed in a similar way.

To create the kernel image:

$ arm-rtems6-objcopy -Obinary hello.exe kernel.img

Copy the kernel image to the SD card.

Make sure you have these lines below, in your config.txt.

dtoverlay=disable-bt
kernel_address=0x200000
kernel=kernel.img

8.2.14.3. SPI Driver#

SPI drivers are registered by the rpi_spi_init(bool bidirectional_mode) function.

#include <assert.h>
#include <bsp.h>

void spi_init(void)
{
  int rv;

  rv = rpi_spi_init(false);
  assert(rv == 0);
}

8.2.14.4. I2C Driver#

I2C drivers are registered by the rpi_setup_i2c_bus() function.

#include <assert.h>
#include <bsp.h>

void i2c_init(void)
{
  int rv;

  rv = rpi_setup_i2c_bus();
  assert(rv == 0);
}

8.2.14.5. Testing using QEMU#

QEMU can be built using RSB. Navigate to <SOURCE_BUILDER_DIR>/rtems and run this command.

$ ../source-builder/sb-set-builder --prefix=<TOOLCHAIN_DIR> devel/qemu

Note: Replace <SOURCE_BUILDER_DIR> and <TOOLCHAIN_DIR> with the correct path of the directories. For example, if you used quick-start section as your reference, these two will be $HOME/quick-start/src/rsb and $HOME/quick-start/rtems/5 respectively,

QEMU along with GDB can be used for debugging, but it only supports Raspberry Pi 2 and the emulation is also incomplete. So some of the features might not work as expected.

Make sure your version of QEMU is newer than v2.6, because older ones don’t support Raspberry Pis.

$ qemu-system-arm -M raspi2 -m 1G -kernel hello.exe -serial mon:stdio -nographic -S -s

This starts QEMU and creates a socket at port localhost:1234 for GDB to connect.

The Device Tree Blob (DTB) is needed to load the device tree while starting up the kernel. The BSP uses information from this file to initialize the drivers.

Make sure you pass in the correct DTB file. There are currently two version of DTB for the Raspberry Pi 2 bcm2709-rpi-2-b.dtb and bcm2710-rpi-2-b.dtb. The bcm2709-rpi-2-b.dtb is for Raspberry Pi 2 Model B and bcm2710-rpi-2-b.dtb is for Raspberry Pi 2 Model B v1.2

We need to pass in the DTB file to GDB before running the example.

In a new terminal, run GDB using

$ arm-rtems6-gdb hello.exe

This will open GDB and will load the symbol table from hello.exe. Issue the following commands in the GDB prompt.

(gdb) tar remote:1234
(gdb) load
(gdb) restore bcm2709-rpi-2-b.dtb binary 0x2ef00000
(gdb) set $r2 = 0x2ef00000

This will connect GDB to QEMU and will load the DTB file and the application.

(gdb) continue

The continue command will run the executable.

Note: Add set scheduler-locking on in GDB if you have any issues running the examples.

raspberrypi

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