kgdb debug with ttyUSB0 instead of ttyS0

DISCUSSION Oliver Graute 4 participants 7 messages Apr 25, 2017 – Apr 29, 2017

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Oliver Graute

author

2017-04-25 21:11 UTC #0 lore raw

Hello list,

i'am using a null modem cable with two usb to serial converts on both ends between my develop and my target machine. The connection is fine. On both machines the serial interface is /dev/ttyUSB0 for this connection.

On the target machine I try to enable kgdboc

echo ttyUSB0 > /sys/module/kgdboc/parameters/kgdboc

but only got:

echo write error: No such device

if I try:

echo ttyS0 > /sys/module/kgdboc/parameters/kgdboc

is not complaining. Some ideas why ttyUSB0 can't be used with kgdb?

Best regards,

Oliver

Mandeep Sandhu

2017-04-25 22:02 UTC #1 lore raw

Quoted 7 lines

echo ttyUSB0 > /sys/module/kgdboc/parameters/kgdboc
but only got:
echo write error: No such device

Is the USB-to-serial device detected on your target? Do you see a ttyUSB0 device node on your target? You can look at the kernel logs on your target when you insert the device. If the kernel has the drivers for it, you should see a device node being created.

-mandeep

Quoted 7 lines

if I try:
echo ttyS0 > /sys/module/kgdboc/parameters/kgdboc
is not complaining. Some ideas why ttyUSB0 can't be used with kgdb?

Quoted 9 lines

Best regards,
Oliver
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Greg KH

2017-04-26 04:37 UTC #2 lore raw

In reply to Oliver Graute

Quoted 12 lines · Oliver Graute

Hello list,
i'am using a null modem cable with two usb to serial converts on both ends between my develop and my target machine. The connection is fine. On both machines the serial interface is /dev/ttyUSB0 for this connection.
On the target machine I try to enable kgdboc
echo ttyUSB0 > /sys/module/kgdboc/parameters/kgdboc
but only got:

Quoted 7 lines

echo write error: No such device
if I try:
echo ttyS0 > /sys/module/kgdboc/parameters/kgdboc
is not complaining. Some ideas why ttyUSB0 can't be used with kgdb?

USB needs interrupts in order to run properly, which kgdb doesn't enable when you stop the target, for obvious reasons :)

Stick to a "real" serial connection and you should be fine.

good luck!

greg k-h

Oliver Graute

author

2017-04-26 11:23 UTC #3 lore raw

Quoted 15 lines · Greg KH

Quoted 14 lines · Oliver Graute
Hello list,
i'am using a null modem cable with two usb to serial converts on both ends between my develop and my target machine. The connection is fine. On both machines the serial interface is /dev/ttyUSB0 for this connection.
On the target machine I try to enable kgdboc
echo ttyUSB0 > /sys/module/kgdboc/parameters/kgdboc
but only got:
echo write error: No such device

Quoted 8 lines

Quoted 5 lines
if I try:
echo ttyS0 > /sys/module/kgdboc/parameters/kgdboc
is not complaining. Some ideas why ttyUSB0 can't be used with kgdb?
USB needs interrupts in order to run properly, which kgdb doesn't enable when you stop the target, for obvious reasons :)

ok that make sense

Quoted 1 line

Stick to a "real" serial connection and you should be fine.

thats not so easy. Even the old notebooks today lacks a "real" serial connection. Perhaps I should use a raspberry as target. There I can get a serial over the gpios.

Best Regards,

Oliver

Greg KH

2017-04-26 12:49 UTC #4 lore raw

Quoted 25 lines · Oliver Graute

Quoted 15 lines · Greg KH
Quoted 14 lines · Oliver Graute
Hello list,
i'am using a null modem cable with two usb to serial converts on both ends between my develop and my target machine. The connection is fine. On both machines the serial interface is /dev/ttyUSB0 for this connection.
On the target machine I try to enable kgdboc
echo ttyUSB0 > /sys/module/kgdboc/parameters/kgdboc
but only got:
echo write error: No such device
Quoted 8 lines
Quoted 5 lines
if I try:
echo ttyS0 > /sys/module/kgdboc/parameters/kgdboc
is not complaining. Some ideas why ttyUSB0 can't be used with kgdb?
USB needs interrupts in order to run properly, which kgdb doesn't enable when you stop the target, for obvious reasons :)

Quoted 7 lines

ok that make sense
Quoted 1 line
Stick to a "real" serial connection and you should be fine.
thats not so easy. Even the old notebooks today lacks a "real" serial connection. Perhaps I should use a raspberry as target. There I can get a serial over the gpios.

Why do you need to use a notebook where Linux works already for kgdb? That's traditionally only used to bring up new hardware platforms.

Also, there is USB serial debugging cables as there is a special mode in the USB 2 and 3 controllers that can be enabled to handle serial messages without interrupts for console/printk early messages that people use. The cables are not cheap to enable this, but worth it if you have to debug this type of target system.

Good luck!

greg k-h

Joe Smith

2017-04-26 21:11 UTC #5 lore raw

The options you suggested are not clear to me. Can you elaborate how I would debug live kernel when all I have on the two systems is usb. Can you list the cable that I can use/order.

Thanks.

Quoted 55 lines · Greg KH

Quoted 6 lines · Oliver Graute
Quoted 5 lines · Greg KH
Quoted 4 lines · Oliver Graute
Hello list,
i'am using a null modem cable with two usb to serial converts on both ends between my develop and my target machine. The connection is
fine.
Quoted 1 line
Quoted 1 line
Quoted 1 line
On both machines the serial interface is /dev/ttyUSB0 for this
connection.
Quoted 9 lines
Quoted 9 lines
Quoted 9 lines
On the target machine I try to enable kgdboc
echo ttyUSB0 > /sys/module/kgdboc/parameters/kgdboc
but only got:
echo write error: No such device
Quoted 7 lines
Quoted 7 lines
Quoted 5 lines
if I try:
echo ttyS0 > /sys/module/kgdboc/parameters/kgdboc
is not complaining. Some ideas why ttyUSB0 can't be used with kgdb?
USB needs interrupts in order to run properly, which kgdb doesn't
enable
Quoted 9 lines
Quoted 1 line
when you stop the target, for obvious reasons :)
ok that make sense
Quoted 1 line
Stick to a "real" serial connection and you should be fine.
thats not so easy. Even the old notebooks today lacks a "real" serial connection. Perhaps I should use a raspberry as target. There I can get a serial over the gpios.
Why do you need to use a notebook where Linux works already for kgdb? That's traditionally only used to bring up new hardware platforms.
Also, there is USB serial debugging cables as there is a special mode in the USB 2 and 3 controllers that can be enabled to handle serial messages without interrupts for console/printk early messages that people use. The cables are not cheap to enable this, but worth it if you have to debug this type of target system.
Good luck!
greg k-h
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JS
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Oliver Graute

author

2017-04-29 11:51 UTC #6 lore raw

In reply to Greg KH

Quoted 2 lines · Greg KH

Why do you need to use a notebook where Linux works already for kgdb? That's traditionally only used to bring up new hardware platforms.

I just used a old notebook as target to learn how-to debug with kgdb. inspired by the debugging Chapter 4 in the LDD3 Book.

Quoted 5 lines

Also, there is USB serial debugging cables as there is a special mode in the USB 2 and 3 controllers that can be enabled to handle serial messages without interrupts for console/printk early messages that people use. The cables are not cheap to enable this, but worth it if you have to debug this type of target system.

can you point us to such a cable?

Best Regards,

Oliver