topic Re: i.MX6Q Boot Mode Selection in i.MX Processors

i.MX6Q Boot Mode Selection

neksn — Mon, 10 Sep 2018 10:08:19 GMT

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_7	CFG1_6	CFG1_5	CFG1_4	CFG1_3	CFG1_2	CFG1_1	CFG1_0	CFG2_7	CFG2_6	CFG2_5	CFG2_4	CFG2_3	CFG2_2	CFG2_1	CFG2_0
0	1	1	0	0	0	0	0	0	0	1	1	1	0	0	0	EMMC
0	1	0	0	0	0	0	0	0	0	1	1	0	0	0	0	USB
0	1	0	0	0	0	0	0	0	0	0	0	1	0	0	0	TF
011X=MMC/eMMC BOOT								0	X0=1-bit X1=4-bit 10=8-bit		01=SD2 BOOT
								0			10=SD3 BOOT
								0			11=SD4 BOOT
010X=SD/eSd BOOT								0	X0=1-bit X1=4-bit		01=SD2 BOOT
								0			10=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

Re: i.MX6Q Boot Mode Selection

igorpadykov — Tue, 11 Sep 2018 01:13:47 GMT

Hi Nelson

for first two questions, boot flow is defined by sd/emmc specifications for bus

width selection (1 - bit is default mode) for example please look at

sect.4.3.1 Wide Bus Selection SD card specification in document on

Q&A: uSDHC capability for SDXC cards in i.MX6S/DL

"For the USB download:" yes, idea is that "once some error happened

with internal boot, it will directly jump to USB mode" and described in

Figure 8-1. Boot flow i.MX6DQ Reference Manual
http://www.nxp.com/docs/en/reference-manual/IMX6DQRM.pdf

Best regards
igor
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Re: i.MX6Q Boot Mode Selection

neksn — Tue, 11 Sep 2018 02:02:49 GMT

Thank you for answer, but in that link, maybe it only simply saying TF card default bit width is 1 bit. not mention eMMC.

But it still not clarify my question, since both 4bit for TF card, and 8bit for eMMC both can work, why lot of design not use it, but instead of default value? or based on what purpose, they select low bitwidth.

My understanding the more width, the higher data rate, isn't it?