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i.MX6Q Boot Mode Selection

Question asked by Nelson Ni on Sep 10, 2018
Latest reply on Sep 10, 2018 by Nelson Ni

Hi,

 

I am learning some development kits, and find some confusing about the boot mode config. Hope some experts can share some ideas. I found some suppliers development kits boot setting as below:

 

CFG1_7CFG1_6CFG1_5CFG1_4CFG1_3CFG1_2CFG1_1CFG1_0CFG2_7CFG2_6CFG2_5CFG2_4CFG2_3CFG2_2CFG2_1CFG2_0
0110000000111000EMMC
0100000000110000USB
0100000000001000TF
011X=MMC/eMMC BOOT    0X0=1-bit
X1=4-bit
10=8-bit
01=SD2 BOOT   
    010=SD3 BOOT   
    011=SD4 BOOT   
010X=SD/eSd BOOT    0X0=1-bit
X1=4-bit
01=SD2 BOOT   
    010=SD3 BOOT   
     11=SD4 BOOT   

For eMMC boot:

My confusing is why they both select 4 bit mode, instead of 8 bit, although the schematic design is 8bit. connect both SD0-SD7. I also see some board set 8bit also can work fine. Does the eMMC can be work under both 4bit and 8bit? what's the difference? If the development kits use 4bits mode, any impact if I change to the 8 bits then? Will the eMMC still working? any impact to the SW load?

 

For SD boot:

Same confusing, as the table, they use 1bit mode, but the schematic connect 4bits SD0-SD3 to the TF card. what will happen if I change to 4 bit boot?

 

For the USB download:

According the user manual, should set the boot_mode[1:0]=0x01, but the board has fixed the boot_mode=0x10, then with above config setting, still can go into USB mode. Does this use the feature "once some error happened with internal boot, it will directly jump to USB mode"? So this config lead the MCU check the unconnected interface, like SD3, MCU find nothing at SD3, then directly go into USB mode. Is this the idea?

 

Thank you

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