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i.MX8M Mini USDHC3 eMMC IO Voltage

Question asked by Omar Hussein on Sep 2, 2019
Latest reply on Sep 3, 2019 by Wigros Sun



I've been reading through the documentation for the i.MX8M Mini boot from eMMC and have some queries about the IO voltage selection. 


Firstly, Table 6-19 of the reference manual states that BOOT_CFG[1] and BOOT_CFG[0] are used to set the IO voltage for USDHC1 and 2 respectively, which I assume corresponds to USDHC ports 1 and 2. However in the Fusemap (Table 6-43) it states that they control the USDHC IO Voltage for Normal Boot Mode and Manufacturer Mode. These seem like different things, unless Normal Boot Mode only uses port 1 and Manufacturer Mode uses port 2? If they are not associated in that way then which of the tables is correct?


Additionally Table 6-19 states that the IO voltage for USDHC3 is set through a fuse that isn't attached to a GPIO, and that it defaults to 3V3. Is there a way to make USDHC3 run at 1V8 before boot, in the case of booting from an eMMC card at 1V8 IO on port 3. The schematics for the dev board show that a 1V8 eMMC card is attached to port 3 and that to get around this restriction the USDHC3 supply is simply tied to 1V8 - is this the recommended solution to the problem? If that is the solution then what is the purpose of having the fuse for the IO voltage selection?