9.2. arm (ARM)¶

9.2.1. 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.

9.2.1.1. 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).

9.2.1.2. 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

9.2.1.3. Clock Driver¶

The clock driver uses the ARMv7-AR Generic Timer.

9.2.1.4. 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.

9.2.1.5. I2C Driver¶

I2C drivers are registered by the i2c_bus_register_imx() function. The I2C driver does not configure the pins.

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

void i2c_init(void)
{
  int rv;

  rv = i2c_bus_register_imx("/dev/i2c-0", "i2c0");
  assert(rv == 0);
}

9.2.1.6. 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.

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

void spi_init(void)
{
  int rv;

  rv =  spi_bus_register_imx("/dev/spi-0", "spi0");
  assert(rv == 0);
}

9.2.1.7. 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.

9.2.1.8. MMC/SDCard Driver¶

The MMC/SDCard driver (uSDHC module) is provided by the libbsd. It is initialized according to the device tree. Pin re-configuration according to the serial clock frequency is not supported. Data transfers are extremely slow. This is probably due to the missing DMA support.

9.2.1.9. 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.