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iMX28: Difference between pswitch usb mode and BM0:3 usb mode?

Question asked by Matthias Moschall on Apr 6, 2016
Latest reply on Apr 6, 2016 by Matthias Moschall

We have a custom board base on the iMX28 EVK which runs smoothly so far. But now we discovered we need to set the fuses for secure boot. This seems only possible while booting through USB OTG.

 

I wonder if there is a difference between the differently initiated USB boot modes. The reference manual describes two methods:

1. Apply high level voltage to PSWITCH for more then 5 seconds to enter "Freescale USB Recovery Mode"

2. Apply low level volatge to BM0:3 for USB Boot Mode

 

What's the difference? We need to write the fuses for secure boot capability! Is this possible with both methods?

 

On our recent board, we configured the BM0:3 pins (0b1001)  for booting from SD-Card. Additionally PSWITCH is tied to VDDXTAL through a 10k resistor and we use a 5V supply only. Everything runs good. My question is, if I need PSWITCH for USB recovery mode (to write also the fuses), will the system also start from SD-Card if PSWITCH has low level voltage and the 5V supply is available? This would make the changes easier!?

 

Thanks for your help.

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