8.2.9. imx (NXP i.MX)¶

This BSP offers only one variant, the imx7. This variant supports the i.MX 7Dual processor and the i.MX 6UL/ULL processor family (with slightly different clock settings). 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 or barebox.

8.2.9.1. Build Configuration Options¶

The following options can be used in the BSP section of the waf configuration INI file. The waf defaults can be used to inspect the values.

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_ECSPI_HZ: The ECSPI clock frequency in Hz (default is 67500000).
IMX_CCM_AHB_HZ: The AHB clock frequency in Hz (default is 135000000).
IMX_CCM_SDHCI_HZ: The SDHCI clock frequency in Hz (default is 196363000).

8.2.9.2. Clock settings for different boards¶

The default clock settings are targeted for an i.MX 7Dual evaluation board using U-Boot. Some other boards with different boot loaders need different settings:

Phytec phyCORE-i.MX 6ULL (system on module) with MCIMX6Y2CVM08AB and a barebox bootloader (version 2019.01.0-bsp-yocto-i.mx6ul-pd19.1.0):

IMX_CCM_IPG_HZ=66000000

IMX_CCM_UART_HZ=80000000

IMX_CCM_AHB_HZ=66000000

IMX_CCM_SDHCI_HZ=198000000

IMX_CCM_ECSPI_HZ=60000000

8.2.9.3. Boot via U-Boot¶

The application executable file (ELF file) must be converted to an U-Boot image. Use the following commands:

arm-rtems6-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

The loadfdt command may be not defined in your U-Boot environment. Just replace it with the appropriate commands to load the device tree at ${fdt_addr}.

8.2.9.4. Boot via barebox¶

The same command like for U-Boot can be used to generate an application image. In a default configuration barebox expects an fdt image called oftree and a kernel image called zImage in the root folder of the bootable medium (e.g. an SD card).

8.2.9.5. Clock Driver¶

The clock driver uses the ARMv7-AR Generic Timer.

8.2.9.6. 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.

8.2.9.7. 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);
}

8.2.9.8. 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);
}

8.2.9.9. 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.

On the Phytec phyCORE-i.MX 6ULL modules the PHY needs an initialization for the clock. A special PHY driver handles that (ksz8091rnb). Add it to your libbsd config like that:

#define RTEMS_BSD_CONFIG_BSP_CONFIG
#define RTEMS_BSD_CONFIG_INIT
SYSINIT_DRIVER_REFERENCE(ksz8091rnb, miibus);
#include <machine/rtems-bsd-config.h>

On chips with two Ethernet controllers, the MDIO lines are shared between the two controllers for a number of chips variants. This is currently supported with some restrictions on the initialization order. For this configuration to work, you have to make sure that the pins are assigned to the Ethernet controller that is initialized first. The initialization order in libbsd depends on the order of the Ethernet controllers in the device tree. So if (for example) fec2 is defined in the device tree sources before fec1, make sure that the MDIO lines are routed to fec2 and that the Ethernet PHYs are a sub-node of fec2 in the device tree.

Note that the clock for the second Ethernet controller is not necessarily enabled in the CCM. On the i.MX6UL/ULL, the clock will be enabled by the startup code if the node that is compatible with fsl,imx6ul-anatop can be found in the device tree. If you have trouble with the second Ethernet controller make sure that the ENET2_125M_EN bit in the CCM_ANALOG_PLL_ENET register is set as expected.

8.2.9.10. 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.

8.2.9.11. 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.