Linux/AM3352: Boot issue

Jeff Schaefer

Part Number: AM3352

Tool/software: Linux

Our design use SYS_BOOT10-15 as inputs. The inputs are simple jumpers that are Open or Short to Ground. These jumpers are used to configure our product and are installed when power is off.

Our design is based on the Beagle Bone Black. Our design is configured to boot MMC1, MMC0, UART0, and lastly USB0. When no jumpers are installed this seems to work fine. When the jumper attached to SYS_BOOT14 is installed most boards boot, but others do not.

We tested this extensively on the Beagle Bone Black and it works. We tested it on the prototype run of our design, it worked. Now that we are in production it seems like about 20% of the boards will not boot with SYS_BOOT14 tied to ground.

Does anyone have any clues?

over 6 years ago

0 Biser Gatchev-XID over 6 years ago

TI__Guru**** 393215 points

SYSBOOT[15:14] determine the main oscillator frequency. Please see Table 26-7 in the AM335x TRM Rev. P. If the SYSBOOT settings are overridden by external signals at POR release time the device will not boot successfully.

0 Jeff Schaefer over 6 years ago in reply to Biser Gatchev-XID

Prodigy 50 points

Thank you for that answer.

I know what the SYS_BOOT Pins do. My question is why do most (80%) of the boards boot properly even when I have SYS_BOOT14 tied to ground? We tested the theory extensively on the beagle bone black and our prototype run (25 boards) and it worked fine. I saw then, and can still see now that there a potential for this problem. I probably should have gated the jumpers using PWRONRESETn, but the FAE that looked at the design said that it would not be a problem. Oh well

I have other unused jumpers that are not connected to SYS_BOOT pins.

0 Biser Gatchev-XID over 6 years ago in reply to Jeff Schaefer

TI__Guru**** 393215 points

Sorry, I can't say what's the reason for this behavior, not having the schematic to look at.

0 Jeff Schaefer over 6 years ago in reply to Biser Gatchev-XID

Prodigy 50 points

Is there any way for me to send you a snipet of the schematic?

0 Biser Gatchev-XID over 6 years ago in reply to Jeff Schaefer

TI__Guru**** 393215 points

You can post it here. Just drag and drop in in the text window, or use the "Insert Code, Attach Files and more... " link on bottom right.

0 Jeff Schaefer over 6 years ago in reply to Biser Gatchev-XID

Prodigy 50 points

Schematic Snipet.pdf

0 Jeff Schaefer over 6 years ago in reply to Jeff Schaefer

Prodigy 50 points

Let me know if you have any questions.

0 Biser Gatchev-XID over 6 years ago in reply to Jeff Schaefer

TI__Guru**** 393215 points

Hi,

Placing a jumper to GND on SYSBOOT[14] forces SYSBOOT[15:14] = 00b. From this combination the ROM code will assume that the main oscillator clock is 19.2MHz instead of 24MHz. The processor will usually boot, however all internal frequencies will be set wrongly. This can cause unpredictable behavior from the device.

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Linux/AM3352: Boot issue