imx6 system boot

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imx6开机启动就进入download模式，有的板子进入文件系统之后会进入download模式。查看datasheet，Chapter 8 System Boot查找原因,记录于此。

freescale论坛有关于这个问题的讨论，有硬件也有软件方面的原因。

参考链接

https://community.nxp.com/thread/316232

https://community.nxp.com/thread/338433

boot mode pin settings

8.2.1 Boot mode pin settings BOOT_MODE is initialized by sampling the BOOT_MODE0 and BOOT_MODE1 inputs on the rising edge of POR_B. After these inputs are sampled, their subsequent state does not affect the contents of the BOOT_MODE internal register. The state of the internal BOOT_MODE register may be read from the BMOD[1:0] field of the SRC Boot Mode Register (SRC_SBMR2). The available boot modes are: Boot From Fuses, serial boot via USB, and Internal Boot. See the table below for settings 根据BOOT_MODE[1:0]引脚的值选择启动类型 BOOT_MODE[1:0] Boot Type 00 Boot From Fuses 01 Serial Downloader 10 Internal Boot 11 Reserved在POR_B引脚的上升沿读取BOOT_MODE0和BOOT_MODE1的值作为启动的模式。如果boot一开始就进入download模式，应该查看POR_B上升沿时，BOOT_MODE, BOOT_CFG引脚配置的值是否正确。

Boot devices(Internal Boot)

当选择为Internal Boot时，根据BOOT_CFG1[7:4]选择启动设备的类型，如果没有选择的设备，则进入download模式。 NOR Flash with External Interface Module (EIM), located on CS0, 16-bit bus width • OneNAND Flash with EIM interface, located on CS0, 16-bits bus width • Raw NAND (MLC and SLC), and Toggle-mode NAND flash through GPMI-2 interface. Page sizes of 2 Kbyte, 4 Kbyte and 8 Kbyte. Bus widths of 8-bit with 2 through 40-bit BCH Hardware ECC (Error Correction) are supported. • SD/MMC/eSD/SDXC/eMMC4.4 via USDHC interface, supporting high capacity cards • EEPROM boot via SPI (serial flash) and I2C(via ECSPI and I2C blocks respectively) The selection of external boot device type is controlled by BOOT_CFG1[7:4] eFUSEs. See the table below for more detailsBOOT_CFG1[7:4] Boot Device 0000 NOR/OneNAND (EIM) 0001 Reserved 0011 Serial ROM (I2C/SPI) 010x SD/eSD/SDXC 011x MMC/eMMC 1xxx Raw NAND

BOOT_CFG其他引脚

BOOT_CFG1,BOOT_CFG2,BOOT_CFG3,BOOT_CFG4引脚进一步确定其他的参数。例如sd/emmc,如下： 8.5.3 Expansion Device The ROM supports booting from MMC/eMMC and SD/eSD compliant devices. 8.5.3.1 Expansion Device eFUSE Configuration SD/MMC/eSD/eMMC/SDXC boot can be performed using either USDHC ports, based on setting of the BOOT_CFG2[4:3] (Port Select) fuse or it's associated GPIO input value at boot. All USDHC ports support eMMC4.3 and eMMC4.4 fast boot.BOOT_CFG2[7:5] 选择SD/EMMC的参数 SD/eSD/SDXC (BOOT_CFG1[5]=0) Bus Width xx0 - 1-bit xx1 - 4-bit SD Calibration Step 00x - 1 delay cells 01x - 1 delay cells 10x - 2 delay cells 11x - 3 delay cells MMC/eMMC (BOOT_CFG1[5]=1) 000 - 1-bit 001 - 4-bit 010 - 8-bit 101 - 4-bit DDR (MMC 4.4) 110 - 8-bit DDR (MMC 4.4) Else - reserved. BOOT_CFG2[4:3] 选择从哪个设备启动 01 - USDHC-2 10 - USDHC-3 11 - USDHC-4