Question, i.MX28 recovery mode

[Aemj]

Dear team,

I would like to ask about i.MX28 recovery mode.

My customer is testing if i.MX28 enters into recovery mode on their own board.

On their board, i.MX28 seems not to enter the recovery mode even when PSWITCH pin is connected to its high level.

When the PSWITCH pin is tied to high, i.MX28 seems not to work during 5 seconds after power on. Then i.MX28 starts boot from its original boot source(SPI Flash).

It seems to be reasonable for i.MX28 not to work during 5 seconds according to the description in reference manual. But after the 5 seconds, i.MX28 does not enter the Recovery mode.

Could you give your advice to make i.MX28 enter recovery mode?

The customer measured the voltage of PSWITH pin, and it was 2.1V at that time.

Thanks,

Miyamoto

[art]

I said "looks strange" since it looks to be inconvenient for a "real life" application. The typical PSWITCH circuitry consists of two parts: one to power up the processor for regular operation, another - to put it to the recovery mode, see below the fragment of the i.MX28 EVK board schematic:

Here S5 is for regular power-up, S6 - for entering recovery mode.

Best Regards,

Artur

[Aemj]

Dear Artur,

Thanks a lot for your support.

I checked with the customer and they decided not to use recovery mode on their board finally.

To ensure that the board does not enter into recovery mode, they plan to design their board as follows.

PSWITCH pin will be pulled down to GND through 100Kohm.

And VDD5V will be supplied until boot-up completes, then supplying 5V to VDD5V will stop on their board.

Could you tell me whether the above is OK?

BR,

Miyamoto

[art]

Yes, it should work OK in case if the valid DCDC_BATT supply voitage is applied as well.

Best Regards,

Artur

[Aemj]

Dear Artur,

Does i.MX28 behave like that, boot from SPI or else, in the case that USB connection is not established at that time?

BR,

Miyamoto

[art]

There are two possible cases.

1. If i.MX28 goes to the recovery mode due to PSWITCH connected to the High level, it first tries to detect an USB connection to Host. If it does not detect an USB connection, it then goes to normal boot mode.

2. If i.MX28 goes to the recovery mode due to unsuccessful boot in normal mode, it stays in recovery mode awaiting for an USB connection.

Best Regards,

Artur

[Aemj]

Dear all,

As for the USB connection, the customer was tested with no USB connection.

Thanks.

They tested again with USB connection.

This time, some of their boards could not go into the recovery mode and it seemed to be caused by the voltage level of PSWITCH.

In the boards which could not go into the recovery mode, i.MX28 started SPI boot right after power-on.

The circuitry around PSWITCH for entering recovery mode is as below.

And they measured the voltage of PSWITCH and VDDXTAL pin.

For the boards which can go into recovery mode;

PSWITCH: 1.81V, VDDXTAL: 1.01V

For the boards which can NOT go into recovery mode;

PSWITCH: 1.77V, VDDXTAL: 0.98V

For test, they forced the supply 2V to PSWITCH pin then i.MX28 could enter into recovery mode.

They have a doubt on the threshold voltage numbers written in Table11-1 in i.MX28 reference manual.

BestRegards,

Miyamoto

[art]

This schematic around the PSWITCH pin looks strange. Typical solution to enter the recovery mode is to tie PSWITCH to 3.3V VDDIO power rail through a 10kOhm resistor with no pulldowns. Please recommend it to the customer.

Best Regards,

Artur

[Aemj]

Dear Artur,

Thanks for you comment.

The customer’s schema is to test if i.MX28 can enter recovery mode.

And it is to provide the divided voltage to PSWITCH.

Could you tell me why the schema looks strange?

BR,

Miyamoto

[art · Accepted solution]

Please make sure that the PSWITCH pin is connected to the High logic level (e.g. to 3.3V VDDIO power rail) through a 10kOhm current limiting resistor to enter the USB recovery mode. Also, make sure that an USB connection to a Host PC is established and active when you are trying to enter the USB recovery mode.

Have a great day,
Artur

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[Yuri]

  Please try to change crystal 24 MHz. USB is frequency sensitive.

Re: Problem with i.MX28 ROM BOOT

Have a great day,
Yuri

[GraceH]

Is the USB connected?

With MX28 EVK board and USB connected, I can enter recovery mode when hold recovery button 5 seconds.

Grace