MWPau
Posts: 2
Joined: Sat Aug 04, 2018 7:34 pm

CM3 eMMC boot delay

Sun Aug 05, 2018 9:23 am

Greetings all,

I'm trying to work out what's causing an approx 13sec delay after power-up of a CM3 on a Waveshare "IO Board Plus".

I'm booting from the CM3's eMMC, and monitoring start progress on the serial console.
After power-on, it takes approx 13sec before i see any output (linux kernel boot log) info on the console.

Does anyone know what causes this delay?

Thanks in advance!

John Westlake
Posts: 84
Joined: Thu Nov 09, 2017 4:34 am

Re: CM3 eMMC boot delay

Sun Aug 05, 2018 1:33 pm

A common issue for first time CM3 hardware developers - I'm betting you missed a pull-up resistor on the HDMI_SDA line :)

See this Thread:-

viewtopic.php?f=98&t=115095

MWPau
Posts: 2
Joined: Sat Aug 04, 2018 7:34 pm

Re: CM3 eMMC boot delay

Sun Aug 05, 2018 3:15 pm

A 2.2k pull up to 3.3v seems to have done the trick.

Is there a recommended resistor value that should be used for this?

Thanks!

aBUGSworstnightmare
Posts: 1087
Joined: Tue Jun 30, 2015 1:35 pm

Re: CM3 eMMC boot delay

Mon Aug 06, 2018 10:19 am

https://www.raspberrypi.org/documentati ... CM_2p0.pdf
On page 12 you only find a note
f Requires external pull-up resistor to 5V as per HDMI spec
CMIO uses ESD5384 HDMI ESD protection
http://www.onsemi.com/pub/Collateral/ESD5384-D.PDF
Based on the parts spec:
R1, R2 Resistance min: 1575, typ: 1750, max: 1925
--> that's why I'm using 1k8 Ohms (to 3.3V as I don't have external HDMI connection). Anyway, your 2k2 Ohms pull-up should be fine.

John Westlake
Posts: 84
Joined: Thu Nov 09, 2017 4:34 am

Re: CM3 eMMC boot delay

Mon Aug 06, 2018 9:20 pm

MWPau wrote:
Sun Aug 05, 2018 3:15 pm
A 2.2k pull up to 3.3v seems to have done the trick.

Is there a recommended resistor value that should be used for this?

Thanks!
If HDMI is not used, then 2K2 is OK, we use 10K...

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