LCD pins/HDMI framer loading

[Gabriel Smolnycki]

The BBB SRM mentions that the LCD pins have an extra load on them due to the HDMI framer and filter caps, and that this could affect operation in other modes. In practice, how great is this effect? In particular, I'm looking to use the UARTs on those pins, and possibly some GPIOs through the PRU.

In a semi-related question, what limits the numbers of capes to 4? If I were to manually load DTOs, would there be any issue using say 8 capes? Is it just that capemgr won't detect the EEPROMs outside of the 0x54 to 0x57 range? I'd like to be able to use 5-6, all custom designs, I'm just wondering if there should be any problem with using that many stacked capes.

[evilwulfie]

If your not going to use the framer try a beagle bone green

On 10/21/2018 6:51 PM, Gabriel Smolnycki wrote:

The BBB SRM mentions that the LCD pins have an extra load on them due to the HDMI framer and filter caps, and that this could affect operation in other modes. In practice, how great is this effect? In particular, I'm looking to use the UARTs on those pins, and possibly some GPIOs through the PRU.

In a semi-related question, what limits the numbers of capes to 4? If I were to manually load DTOs, would there be any issue using say 8 capes? Is it just that capemgr won't detect the EEPROMs outside of the 0x54 to 0x57 range? I'd like to be able to use 5-6, all custom designs, I'm just wondering if there should be any problem with using that many stacked capes.

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[a...@autopogo.com]

I've never had an issue with 20MHz signals on the LCD pins with the HDMI chip off.

[Gabriel Smolnycki]

On Monday, October 22, 2018 at 10:16:43 AM UTC-4, a...@autopogo.com wrote:

I've never had an issue with 20MHz signals on the LCD pins with the HDMI chip off.

This is what I suspected, that the framer doesn't actually load down the pins that much. I assume by "off" you mean turned off via I2C0?

[Andrew Pikul]

I meant in the device tree. I would assume it never started, to be honest. Theoretically it might be on...

Andrew J. Pikul

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(800) 565 4026

autopogo.com

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"All the devil requires is acquiescence... not struggle, not conflict. Acquiescence."

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[Gabriel Smolnycki]

On Monday, October 22, 2018 at 3:27:06 PM UTC-4, Andrew Pikul wrote:

I meant in the device tree. I would assume it never started, to be honest. Theoretically it might be on...

Ahh I see. Right then, definitely make sure to turn off the HDMI virtual cape.

Do you know anything about the cape # limitation? I'm find if the DTOs don't load automatically, although it would be nice if they did.

[Andrew Pikul]

Unfortunately no, sorry. If you don't get a reply here post again or ask on #beagle ilon IRC or BBB.io's webchat.

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[Robert Nelson]

They can load automatically, if the cape's eeprom has a proper id and
we know about that id so u-boot can properly disable any conflicting
interfaces.

Regards,

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Robert Nelson
https://rcn-ee.com/

[Gabriel Smolnycki]

On Monday, October 22, 2018 at 8:48:21 PM UTC-4, RobertCNelson wrote:

They can load automatically, if the cape's eeprom has a proper id and
we know about that id so u-boot can properly disable any conflicting
interfaces.

I'm mostly concerned about loading extra capes, beyond the stated limit of 4. I'm guessing that the only real limit is that capemgr doesn't search I2C addresses outside of 0x54 to 0x57, and therefore won't "see" the additional EEPROMs. Of course, I can manually load as many devices through DTOs as I want Mainly I'm looking to see if there's any *hardware* limitations to loading 5+ capes (seems unlikely), or any software limitations (which seems somewhat likely).

I guess the big concern with the capes is, I'm continuing to add hardware to my system and I'm trying to determine what I might need to modify to ensure it loads properly at boot. If using more than 4 capes means I have to load the DTOs manually, I can do that, but it would be nice to not have to do that.