基于Yocto Krogoth为i.MX.6自定义裸机单板构建BSP层问询

Hey there! Since you’ve already got hands-on experience building Linux images and the Yocto SDK for the Nitrogen6x with Krogoth, you’re already halfway there. Let’s walk through how to create a custom BSP layer for your upcoming bare-metal i.MX.6 board—even with the processor chip still TBD.

Before diving into Yocto configs, you’ll need to nail down the specifics of your custom board:

• Exact i.MX.6 variant (e.g., i.MX6DL, i.MX6Q, i.MX6SL)—each has slightly different peripherals and memory maps.
• Core peripherals for debugging and boot: UART port (for early debug output), boot medium (SD card, eMMC, or SPI flash), power management IC (PMIC), and DDR configuration.
• Any custom peripherals you plan to support (GPIO, I2C sensors, etc.)—these will drive your driver needs later.

Yocto relies on layers for modularity, so let’s start by spinning up your dedicated BSP layer:

• Run this command from your Yocto build directory to generate a skeleton layer:

  bitbake-layers create-layer meta-custom-imx6-baremetal
  

• Add the new layer to your conf/bblayers.conf file—make sure it comes after meta-freescale and meta-freescale-3rdparty to inherit their i.MX.6 base configurations.

Every board needs a machine config file to tell Yocto what it’s dealing with:

• Create meta-custom-imx6-baremetal/conf/machine/custom-imx6-baremetal.conf
• Start by inheriting the base config for your eventual i.MX.6 variant (swap imx6sdl.inc for your chip’s include file once you know it):

  require conf/machine/include/imx6sdl.inc
  require conf/machine/include/imx-base.inc
  
  MACHINE_NAME = "custom-imx6-baremetal"
  MACHINE_FEATURES = "serial usbgadget usbhost vfat" # Adjust based on your board
  SERIAL_CONSOLE = "115200 ttymxc0" # Match your UART port
  

• Since this is a bare-metal setup, you can omit Linux kernel-related configs unless you plan to add a kernel later.

Yocto can build bare-metal binaries too—you just need to define recipes for your code:

• Create a recipe directory structure like meta-custom-imx6-baremetal/recipes-baremetal/my-baremetal-app
• Inside that, make my-baremetal-app.bb with content like this (adjust paths and flags to match your code):

  SUMMARY = "Custom bare-metal application for i.MX.6"
  DESCRIPTION = "Bare-metal firmware targeting our custom i.MX.6 board"
  LICENSE = "MIT"
  LIC_FILES_CHKSUM = "file://${COMMON_LICENSE_DIR}/MIT;md5=0835ade698e0bcf8506ecda2f7b4f302"
  
  SRC_URI = "file://main.c \
             file://linker.ld \
             file://startup.S"
  
  S = "${WORKDIR}"
  
  # Use Yocto's cross-compiler for ARM
  TARGET_PREFIX = "arm-poky-linux-gnueabi-"
  CC = "${TARGET_PREFIX}gcc"
  LD = "${TARGET_PREFIX}ld"
  OBJCOPY = "${TARGET_PREFIX}objcopy"
  
  # Compilation flags for bare-metal (no OS, no standard libraries)
  CFLAGS += "-march=armv7-a -mfloat-abi=hard -mfpu=neon -nostdlib -ffreestanding"
  LDFLAGS += "-T ${S}/linker.ld"
  
  do_compile() {
      ${CC} ${CFLAGS} -c ${S}/startup.S -o startup.o
      ${CC} ${CFLAGS} -c ${S}/main.c -o main.o
      ${LD} ${LDFLAGS} startup.o main.o -o ${B}/my-baremetal-app.elf
      ${OBJCOPY} -O binary ${B}/my-baremetal-app.elf ${B}/my-baremetal-app.bin
  }
  
  do_install() {
      install -d ${D}/firmware
      install -m 0644 ${B}/my-baremetal-app.bin ${D}/firmware/
  }
  
  FILES_${PN} = "/firmware/*"
  

• Place your bare-metal source files (main.c, startup.S, linker.ld) in the same recipe directory alongside the .bb file.

If you plan to use U-Boot to load your bare-metal binary (instead of booting directly from ROM), you’ll need to customize U-Boot for your board:

• Create a .bbappend file to extend the existing U-Boot recipe: meta-custom-imx6-baremetal/recipes-bsp/u-boot/u-boot_%.bbappend
• Add your custom U-Boot config and patches:

  SRC_URI += "file://custom-imx6-config.cfg \
              file://0001-custom-board-support.patch"
  
  UBOOT_CONFIG += "custom"
  UBOOT_CONFIG[custom] = "custom-imx6-config_defconfig"
  

• Your patch should add board-specific files (like board/mycompany/custom-imx6/) to U-Boot, including the board config and pinmux settings.

Once everything is set up:

• Set your machine in local.conf:

  MACHINE = "custom-imx6-baremetal"
  

• Build your bare-metal app with:

  bitbake my-baremetal-app
  

• Grab the binary from tmp/deploy/images/custom-imx6-baremetal/my-baremetal-app.bin
• Flash it to your boot medium or load it via U-Boot using load mmc 0:1 0x10000000 my-baremetal-app.bin; go 0x10000000 to test.

• Steal inspiration from meta-freescale/conf/machine/nitrogen6x.conf—it has pre-configured settings for i.MX.6 that you can adapt to your board (like serial console, PMIC settings).
• If you run into peripheral issues, check the Nitrogen6x’s device tree or U-Boot board files—they’ll give you a reference for how to configure i.MX.6 hardware in Yocto.

内容的提问来源于stack exchange，提问作者user12345