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Can't boot when serial cable is connected to powered off pc

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paulchany
Posts: 123
Joined: 10 Jul 2009, 15:48
Location: Serbia
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Can't boot when serial cable is connected to powered off pc

Post by paulchany »

My Bubba2 is connected with an USB-based serial adaptor ( USB connector is at the pc side, on b2 side the cable is solded on to motherboard of b2 ) to my PC.

I have exactly this cable:
FTDI Chip
TTL-232RG-VREG3V3-WE
USB to TTL Serial Cable-1.8m
Wire End Version


When the serial adaptor is plugged into my powered off PC then the B2 ( live-USB ) fails to boot.

When I disconnect the serial cable from my powered off pc, then B2 ( live-USB ) is booted successfully.

When the serial adaptor is plugged into my powered on PC then the B2 ( live-USB ) is booted successfully too.

Can this behavior avoided so I can boot live-USB on B2 regardless of whether is b2 connected to powered off or powered on pc?
Best, Pali
Gordon
Posts: 1461
Joined: 10 Aug 2011, 03:18

Re: Can't boot when serial cable is connected to powered off

Post by Gordon »

Do you have a powered USB hub in between?

My guess is that with the computer powered down whatever is send through the serial connection is echoed back, essentially meaning you are pressing keys causing u-boot to go into manual mode waiting for you to enter a proper boot command. For this to happen, this does imply that the FTDI chip must receive power. Remove that power source and it should behave the same as with the open ended cable.
paulchany
Posts: 123
Joined: 10 Jul 2009, 15:48
Location: Serbia
Contact:

Re: Can't boot when serial cable is connected to powered off

Post by paulchany »

No, I have not any hardware ( eg. powered USB hub in between ), just the cable from B2 to the USB port of powered off PC.
However, the PC has a 0/I switch at back side which I leave in 'I' position always. But, again, the PC get it's power from an extension cord which have a switch too, that I always leave in off position at night.
Although I powered off pc, the serial cable still receive from pc some power, say I forgot to observe whether I tried to boot B2 when this switch was in off, or on position.

Anyway, I shall try to leave O/I switch of PC in 'O' position to see, can I boot then B2 successfully. Thank you for explanation.
Best, Pali
Gordon
Posts: 1461
Joined: 10 Aug 2011, 03:18

Re: Can't boot when serial cable is connected to powered off

Post by Gordon »

Come to think about it, I think you should be able to verify this the other way round. Just ssh into the B2 from another computer and use something like screen to write stuff to ttyS0. If it displays what you are typing, it is echoing. If you see other/random stuff appearing, chances are there is a grounding issue.
paulchany
Posts: 123
Joined: 10 Jul 2009, 15:48
Location: Serbia
Contact:

Re: Can't boot when serial cable is connected to powered off

Post by paulchany »

I did that: I ssh into B2 from my desktop linux system and issue:
# screen /dev/ttyS0 115200

then I type some characters, like 'qwert' but nothing appeares out there. 'Enter' doesn't has any effect too.

Interesting thing is, when I type Ctrl+A and '\' nothing happen, I can't close screen session this way, but only with 'Ctrl+A' and 'Ctrl+D'.

Sometimes, when I use this serial connection, but without ssh from my desktop pc, that is connected to B2 with this serial cable:
- start a xterm window as root user on pc
- issue command 'screen /dev/ttyUSB0 115200'

then I see nothing but empty window.
Then I hit Enter few times and see these:
This
3-gentoo-b2b2) 19:08:35
b2 (Linux ppc 4.1.3-gen

This is b2 (Linux ppc 4.1.3-gentoo-b2) 19:08:37

b2 login:

Thisgin:

Th login:

This is b2 (Linux ppc

This is
Then I login blindly with 'root' and enter password, and finally get these:
Last login: Tue Au8.50.163 on =============================================== o Gentoo Lin |
====rmitted by a==
| ===========
So maybe something is wrong with my serial connection?
Best, Pali
Gordon
Posts: 1461
Joined: 10 Aug 2011, 03:18

Re: Can't boot when serial cable is connected to powered off

Post by Gordon »

The blank screen is normal, because you only see output that is generated after you connect the terminal. The dropping of characters does imply a bad connection somewhere though. Do you get login failures as well?
paulchany
Posts: 123
Joined: 10 Jul 2009, 15:48
Location: Serbia
Contact:

Re: Can't boot when serial cable is connected to powered off

Post by paulchany »

I do not get login failures as well.

I tried boot B2 when my PC is powered off with back side switch in 'O' ( off ) position, but still can't boot B2. The only possibility is to un-plug the USB to TTL Serial Cable from my PC and just then can I boot B2 successfully.

I just connect with serial console from my PC like this:
Start xterm with root privileges.
Issue command:
screen /dev/ttyUSB0 115200
get a blank screen. Here I must hit Enter after about 30 sec, then I get login prompt:
b2 login:
Then I login as root user:
b2 login: root
hit Enter and get this:
assword: root
Here I enter root password and get this:
Aug 19 07:31====================================ux for the B2 miniserve |
| ntainer: sa@deciban.co========================TELY NO WARR==========================
| Pál ==============

0m
This is not a normal shell behavior.
So I can login every time but after login I get the 'messed up shell'.
May it have to do with IRQ settings on B2?
Best, Pali
Gordon
Posts: 1461
Joined: 10 Aug 2011, 03:18

Re: Can't boot when serial cable is connected to powered off

Post by Gordon »

You most likely have a bad connection on the Tx wire from your B2

If you'd had trouble sending characters as well it would have been the ground wire ;)
paulchany
Posts: 123
Joined: 10 Jul 2009, 15:48
Location: Serbia
Contact:

Re: Can't boot when serial cable is connected to powered off

Post by paulchany »

I will soon examine the solder joints on my B2.
Best, Pali
paulchany
Posts: 123
Joined: 10 Jul 2009, 15:48
Location: Serbia
Contact:

Re: Can't boot when serial cable is connected to powered off

Post by paulchany »

paulchany wrote:I will soon examine the solder joints on my B2.
Image
It is look like the solder joints are good enough, right?
Best, Pali
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