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<title>EHCI debugging on the BeagleBone Black</title>
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<div class="section">
<h1 id="pagetop">EHCI debugging on the BeagleBone Black</h1>
<p><a href="index.html">Back to previous index</a></p>
</div>
<div class="section">
<h1>EHCI debugging</h1>
<ol class="toc">
<li><a href="#FindUSBportonthetargetthatsupportsEHCIdebug">Find
USB port on the target that supports EHCI debug</a></li>
<li><a href="#InitialsetupofBBBtoactasEHCIdebugdongle">Initial
setup of BBB to act as EHCI debug dongle</a></li>
<li><a href="#PatchBBBsgdbgpmoduleoptionalbuthighlyrecommended">Patch
BBB's <tt>g_dbgp</tt> module (optional, but highly recommended)</a></li>
<li><a href="#ConfigurelibrebootwithEHCIdebug">Configure
libreboot with EHCI debug</a>
<ol>
<li><a href="#SelectingHCDIndexandUSBDebugport">Selecting
<tt>HCD Index</tt> and <tt>USB Debug port</tt></a></li>
</ol></li>
<li><a href="#Howtogetthedebuglogs">How to get the debug
logs</a></li>
<li><a
href="#EnebleEHCIDebugonthetargetskerneloptionalrecommended">Eneble
EHCI Debug on the target's kernel (optional, recommended)</a></li>
<li><a href="#References">References</a></li>
</ol>
<p>If your computer does not boot after installing libreboot, it is
very useful to get debug logs from it, from the payload (grub) and/or
the kernel (if gets to there). All of them stream debug logs on the
available serial (RS-232) by default. However, most of todays laptops
lack RS-232 port. The other option is to stream the logs to USB EHCI
debug port.</p>
<p>This section explains step-by-step how to setup BBB as a
“USB EHCI debug dongle” and configure libreboot and the
linux kernel to stream logs to it (TODO: grub).</p>
<p>I will refer to three computers:</p>
<ul>
<li><b>host</b> - this is the computer you use, have
tools, compiler, Internet, etc</li>
<li><b>BBB</b> - Beaglebone Black (rev. B or higher, i
use rev. C)</li>
<li><b>target</b> - the computer you are trying to
install liberboot</li>
</ul>
<h3 id="FindUSBportonthetargetthatsupportsEHCIdebug">Find USB port
on the target that supports EHCI debug</h3>
<p>
Not all USB controllers support EHCI debug (see: <a
href="http://www.coreboot.org/EHCI_Debug_Port#Hardware_capability">EHCI
Debug Port</a> ). Even more, if a USB controller supports EHCI debug, it
is available only <b>on a single port</b> that might or might
not be exposed externally.
</p>
<ul>
<li>You need running OS (GNU/Linux) on your target for this step
(If you’ve flashed libreboot and it does not boot, you have to
flush back the stock bios)</li>
<li>You need USB memory stick (the data on it will not be
touched).</li>
<li>The EHCI debugging can not be done through external hub, BBB
must be connected directly to the debug port of the controller (so, no
hubs)</li>
</ul>
<ul>
<li>Download<sup class="footnote"><a href="#___fn1">1</a></sup> <a
href="http://www.coreboot.org/pipermail/coreboot/attachments/20080909/ae11c291/attachment.sh">this</a>
shell script.
</li>
</ul>
<ol>
<li>Plug the usb stick in the first available usb port</li>
<li>Run the script, you will get output similar to following:</li>
<pre>The following PCI devices support a USB debug port (says lspci): 0000:00:1a.0 0000:00:1d.0
The following PCI devices support a USB debug port (says the kernel): 0000:00:1a.0 0000:00:1d.0
*PCI device 0000:00:1a.0, USB bus 3, USB physical port 1*
*PCI device 0000:00:1d.0, USB bus 4, USB physical port 2*
Currently connected high-speed devices:
/: Bus 04.Port 1: Dev 1, Class=root_hub, Driver=ehci-pci/2p, 480M
|__ Port 1: Dev 2, If 0, Class=Hub, Driver=hub/8p, 480M
|__ Port 7: Dev 14, If 0, Class=Hub, Driver=hub/4p, 480M
|__ Port 1: Dev 15, If 0, Class=Hub, Driver=hub/4p, 480M
|__ Port 3: Dev 17, If 0, Class=Hub, Driver=hub/2p, 480M
|__ Port 4: Dev 18, If 0, Class=Hub, Driver=hub/4p, 480M
/: Bus 03.Port 1: Dev 1, Class=root_hub, Driver=ehci-pci/2p, 480M
|__ Port 1: Dev 2, If 0, Class=Hub, Driver=hub/6p, 480M
/: *Bus 01*.Port 1: Dev 1, Class=root_hub, Driver=xhci_hcd/4p, 480M
|__ *Port 3: Dev 31, If 0, Class=Mass Storage, Driver=usb-storage, 480M*
</pre>
<li>The buses the support debug are Bus 3 (0000:00:1a.0) on Port 1
and Bus 4 (0000:00:1d.0) on port 2. Your usb stick is plugged on Bus
1, Port 3</li>
<li>Repeat the steps, plugging the USB stick in the next available
port</li>
<li>Go through all available ports and remember(write down) those
for which bus/port of the usb stick matches one of the bus/port that
support debug (bold).</li>
</ol>
<p>Remember (write down) for each port (external plug) you found
that supports debug: <b>PCI device id, the bus id, the port number, and
the physical location of the usb plug.</b></p>
<p>If you do not find a match, you can not get debug over EHCI.
Sorry.</p>
<p id="___fn1" class="footnote">
<sup>1</sup> The guys from coreboot were talking about including the
script in coreboot distribution (check the status).
</p>
<h3 id="InitialsetupofBBBtoactasEHCIdebugdongle">Initial setup of
BBB to act as EHCI debug dongle</h3>
<p>BBB must be powered with a barrel power connector since the
mini-B USB plug will be used for the EHCI debug stream. So you will
need:</p>
<ul>
<li>power supply (5V, 2A(10W) is sufficient).</li>
<li>an extra usb cable: A to mini-B</li>
</ul>
<p>
(On BBB) The linux kernel includes module (g_dbgp that enables one of the usb ports on a computer to behave as EHCI
debug dongle. Make sure you have this module available on your BBB
(Debian 7.8 that comes with BBB should have it), if not, you should
compile it yourself (see next section):
</p>
<pre>ls /lib/modules/3.8.13-bone70/kernel/drivers/usb/gadget/g_dbgp.ko</pre>
<p>
Unload all other
g_*
modules:
</p>
<pre># lsmod
# rmmod g_multi
...
</pre>
<p>
Then load
g_dbgp
:
</p>
<pre># modprobe g_dbgp
# lsmod # should show that g_dbgp is loaded, and no other g_*
</pre>
<p>
Plug the mini-B side of the USB cable in your BBB and the A side in
your target. Then one of the usb devices on your target (with
lsusb
) should be:
</p>
<pre>Bus 001 Device 024: ID 0525:c0de Netchip Technology, Inc.</pre>
<p>If you see the device on the target, you are good to continue to
the next step.</p>
<h3 id="PatchBBBsgdbgpmoduleoptionalbuthighlyrecommended">
Patch BBB’s
g_dbgp
module (optional, but highly recommended)
</h3>
<p>
For the reasons why you need this, see: <a
href="http://www.coreboot.org/EHCI_Gadget_Debug">EHCI Gadget Debug</a>.<br />Make
sure that you have cross compiling environment for
arm-linux-gnueabihf
setup on your <em>host</em>.
</p>
<ul>
<li>On BBB: uname -r - this will give you version
number like 3.8.13-bone70 (I will refer to this as: $mav.$miv-$lv:
where mav=3.8, miv=13, lv=bone70
</li>
<li>Get the BBB kernel ready on your host for cross-compiling:</li>
</ul>
<pre>$ cd $work_dir
$ git clone https://github.com/beagleboard/kernel.git
$ cd kernel
$ git checkout $mav (see above)
$ ./patch.sh
$ wget http://arago-project.org/git/projects/?p=am33x-cm3.git\;a=blob_plain\;f=bin/am335x-pm-firmware.bin\;hb=HEAD -O kernel/firmware/am335x-pm-firmware.bin
$ cp configs/beaglebone kernel/arch/arm/configs/beaglebone_defconfig
</pre>
<ul>
<li>Download the patch from <a
href="http://www.coreboot.org/images/8/88/Ehci-debug-gadget-patches.tar.gz">here</a></li>
<li>tar -xf Ehci-debug-gadget-patches.tar.gz (will
create dir: usbdebug-gadget)</li>
<li>Note that there are two patches (patch_1 and patch_2) for each
of the two different version of the kernel (3.8 and 3.10). I will use
3.8. (If using kernel 3.12 patch_1 is not needed)</li>
<li>cd kernel (note that this is one more level: you
should be in $work_dir/kernel/kernel)</li>
<li>Apply the patches:</li>
</ul>
<pre>
git apply ../usbdebug-gadget/v3.8-debug-gadget/0001-usb-dbgp-gadget-Fix-re-connecting-after-USB-disconne.patch
git apply ../usbdebug-gadget/v3.8-debug-gadget/0002-usb-serial-gadget-no-TTY-hangup-on-USB-disconnect-WI.patch
;
make ARCH=arm CROSS_COMPILE=arm-linux-gnueabihf- beaglebone_defconfig -j4@
</pre>
<ul>
<li>
You should also apply the linux-libre <i>deblob</i> script to turn it into linux-libre
(deletes all the blobs from the linux kernel).
<a href="http://www.fsfla.org/ikiwiki/selibre/linux-libre/">fsfla website</a>
- see <a href="http://www.fsfla.org/svn/fsfla/software/linux-libre/scripts/">scripts</a>.
</li>
<li>Get your current BBB kernel config (from: /boot/config-<ver>)
and copy it to your host as $work_dir/kernel/kernel/.config</li>
<pre>
make ARCH=arm CROSS_COMPILE=arm-linux-gnueabihf- oldconfig - all default answers</pre>
<li>Set proper version number:
<ul>
<li>On your host, edit $work_dir/kernel/kernel/.config
(the one you’ve just copied from BBB), find the line CONFIG_LOCALVERSION="<something
or empty>" and change it to CONFIG_LOCALVERSION="-$lv",
so it will look something like: CONFIG_LOCALVERSION="-bone70"</li>
</ul>
</li>
<li>Also, make sure that: CONFIG_USB_G_DBGP=m (If
not, make menuconfig, and set @Device Drivers-> USB
Support -> USB Gadget Support -> EHCI Debug Device Gadget=m</li>
<li>Build the module:</li>
</ul>
<pre>
$ make ARCH=arm CROSS_COMPILE=arm-linux-gnueabihf- -j4 (is it possoble to build only the gadget modules)
$ mkdir ../tmp && make ARCH=arm CROSS_COMPILE=arm-linux-gnueabihf- INSTALL_MOD_PATH=../tmp modules_install
</pre>
<ul>
<li>on BBB, backup /lib/modules/3.8.13-bone70/kernel/drivers/usb/gadget
(i.e. mv
/lib/modules/3.8.13-bone70/kernel/drivers/usb/gadget $HOME)
</li>
<li>copy the freshly compiled usb/gadget dir to /lib/modules/3.8.13-bone70/kernel/drivers/usb</li>
<li>restart BBB</li>
<li>Remove all g_* modules (rmmod
g_<>)
</li>
<li>modprobpe g_dbgp</li>
</ul>
<h3 id="ConfigurelibrebootwithEHCIdebug">Configure libreboot with
EHCI debug</h3>
<p>
Libreboot(coreboot) should be configured with debug turned on and to
push debug messages to the EHCI debug port.<br />If you’ve
downloaded the binary distribution, you can check if it is properly
configured in the following way:
</p>
<ul>
<li>Go to the libreboot dist root directory cd
$libreboot_bin</li>
<li>Locate the rom image for your target (I will call it: $img_path)
</li>
<li>Running the following command will extract the config in a
file ./my_config:
</li>
</ul>
<pre>
./cbfstool/i686/cbfstool $img_path extract -n config -f ./my_config
</pre>
<ul>
<li>Make sure that the following params in the config are set as
following:</li>
</ul>
<pre>
CONFIG_USBDEBUG=y (Generic Drivers -> USB 2.0 EHCI debug dongle support)
CONFIG_USBDEBUG_IN_ROMSTAGE=y (Generic Drivers -> Enable early (pre-RAM) usbdebug)
CONFIG_USBDEBUG_HCD_INDEX=<HCD Index of usb controller - see below> (Generic Drivers -> Index for EHCI controller to use with usbdebug)
CONFIG_USBDEBUG_DEFAULT_PORT=<USB Debug port - see below> (Generic Drivers -> Default USB port to use as Debug Port)
</pre>
<p>
The following three are behind radio button in the menu. Only the first
one<sup class="footnote"><a href="#___fn2">2</a></sup> should be = y
</p>
<pre>
USBDEBUG_DONGLE_STD=y (Generic Drivers -> Type of dongle (Net20DC or compatible) -> Net20DC or compatible)
CONFIG_USBDEBUG_DONGLE_BEAGLEBONE=n (Generic Drivers -> Type of dongle (Net20DC or compatible) -> BeagleBone)
CONFIG_USBDEBUG_DONGLE_BEAGLEBONE_BLACK=n (Generic Drivers -> Type of dongle (Net20DC or compatible) -> BeagleBone Black)
</pre>
<p id="___fn2" class="footnote">
<sup>2</sup> The g_dbgp module on BeagleBone Black (Rev. C) reports it self as Net20DC, the
other options are for older BB(B) - ver1. This is documented <a
href="https://johnlewis.ie/coreboot-ehci-debug-gadget-demonstration/">here</a>
(also tested/verified).
</p>
<p>
Then:<br />
<pre>
CONFIG_CONSOLE_USB=y (Console -> USB dongle console output)
</pre>
</p>
<p>
Also
Debugging ---> Output verbose XYZ
) (<b>FIXME</b> somebody verify these):
</p>
<pre>
CONFIG_DEBUG_CBFS=y (Output verbose CBFS debug messages )
CONFIG_HAVE_DEBUG_RAM_SETUP=y (??? What/where is this)
CONFIG_DEBUG_RAM_SETUP=y (Output verbose RAM init debug messages)
CONFIG_DEBUG_SMI=y (Output verbose SMI debug messages)
CONFIG_DEBUG_ACPI=y (Output verbose ACPI debug messages )
CONFIG_DEBUG_USBDEBUG=y (Output verbose USB 2.0 EHCI debug dongle messages)
</pre>
<p>If some of the above mentioned configuration options are not as
specified, you have to configure and compile libreboot yourself. Please
refer to the doc(<b>FIXME: link</b> about compiling libreboot.</p>
<h4 id="SelectingHCDIndexandUSBDebugport">
Selecting
HCD Index
and
USB Debug port
</h4>
<p>
This applies (and works) only if the USB controller that supports debug
(found in the first section) is from Intel.<br />If the PCI ID of the
port you found in the first section is
0000:00:1a.0
or
0000:00:1d.0
, you are ok. Otherwise you have to try without guarantee that will
work.
</p>
<p>
If the externally exposed port is on a bus with
PCI ID == 0000:00:1a.0
then for
CONFIG_USBDEBUG_HCD_INDEX
choose 2, otherwise choose 0
.
</p>
<p>
For
CONFIG_USBDEBUG_DEFAULT_PORT
choose the port from the first section that correspond to the
PCI ID
</p>
<p>
Notes:<br />The above is based on the implementation of
coreboot/src/southbridge/intel/common/usb_debug.c : pci_ehci_dbg_dev()
.<br />This is enough as it applies for the supported GM45/G45
Thinkpads. coreboot support some other contollers too, but they are
irellevent for libreboot (for now).
</p>
<ul>
<li>On T500 (with switchable GPU) the debug ports for both intel
controllers is exposed.</li>
<li>On x200t the debug ports for both intel controllers is
exposed.</li>
</ul>
<h3 id="Howtogetthedebuglogs">How to get the debug logs</h3>
<ul>
<li>Plug the USB cable in the target’s debug port (the one
you found in step 1) and BBB’s mini-B USB</li>
<li>Make sure no other then g_dbgp of the g_*
modules is loaded on your BBB
</li>
<li>On the BBB:</li>
</ul>
<pre>
stty -icrnl -inlcr -F /dev/ttyGS0
cat /dev/ttyGS0
</pre>
<ul>
<li>Power on the target with libreboot</li>
<li>You should see debug logs comming on your BBB console</li>
</ul>
<p>
Note that this is not permanent on BBB, if you reboot it, you have to
rmmod g_*
and
modprobe g_dbgp
</p>
<h3 id="EnebleEHCIDebugonthetargetskerneloptionalrecommended">Eneble
EHCI Debug on the target’s kernel (optional, recommended)</h3>
<p>You have to know how to compile kernel for your target.</p>
<ol>
<li>Check if early debugging is already enabled: grep
CONFIG_EARLY_PRINTK_DBGP /boot/config-<ver></li>
<li>If enabled, you do not have to compile the kernel (skip this
step). Otherwise, prepare kernel source for your distribution and
select (Kernel hacking -> Early printk via EHCI debug
port). Compile and install the new kernel.
</li>
<li>Edit your grub configuration and add following to the kenel
parameters<sup class="footnote"><a href="#___fn20">20</a></sup><sup
class="footnote"><a href="#___fn21">21</a></sup>: earlyprintk=dbgp,keep.
Also, try: earlyprintk=dbgp<N>,keep where N
is the debug port id if the first does not work.
</li>
</ol>
<h3 id="References">References</h3>
<p id="___fn10" class="footnote">
<sup>10</sup> <a href="http://www.coreboot.org/EHCI_Debug_Port">EHCI
Debug Port</a>
</p>
<p id="___fn11" class="footnote">
<sup>11</sup> <a
href="https://johnlewis.ie/coreboot-ehci-debug-gadget-demonstration/">coreboot
EHCI debug gadget demonstration</a>
</p>
<p id="___fn12" class="footnote">
<sup>12</sup> <a href="http://www.coreboot.org/EHCI_Gadget_Debug">EHCI
Gadget Debug</a>
</p>
<p id="___fn13" class="footnote">
<sup>13</sup> <a
href="http://www.coreboot.org/images/8/88/Ehci-debug-gadget-patches.tar.gz">Ehci-debug-gadget-patches.tar.gz</a>
</p>
<p id="___fn14" class="footnote">
<sup>14</sup> <a
href="http://wiki.beyondlogic.org/index.php/BeagleBoneBlack_Building_Kernel">Compiling
the BeagleBone Black Kernel</a>
</p>
<p id="___fn15" class="footnote">
<sup>15</sup>
http://dumb-looks-free.blogspot.ca/2014/06/beaglebone-black-bbb-compile-kernel.html
</p>
<p id="___fn16" class="footnote">
<sup>16</sup>
http://dumb-looks-free.blogspot.fr/2014/06/beaglebone-black-bbb-kernal-headers.html
</p>
<p id="___fn17" class="footnote">
<sup>17</sup> <a href="http://elinux.org/Building_BBB_Kernel">Building
BBB Kernel</a>
</p>
<p id="___fn18" class="footnote">
<sup>18</sup>
http://komposter.com.ua/documents/USB-2.0-Debug-Port%28John-Keys%29.pdf
</p>
<p id="___fn19" class="footnote">
<sup>19</sup> <a href="http://cs.usfca.edu/~cruse/cs698s10/">Exploring
USB at the Hardware/Software Interface</a>
</p>
<p id="___fn20" class="footnote">
<sup>20</sup>
https://www.kernel.org/doc/Documentation/x86/earlyprintk.txt
</p>
<p id="___fn21" class="footnote">
<sup>21</sup> https://wiki.ubuntu.com/Kernel/Debugging/USBearlyprintk
</p>
<p>
<b>TODO</b>:
</p>
<ol>
<li>grub does not send messages to EHCI debug. Investigate.</li>
<li>The section “Configure libreboot with EHCI debug”
can be skipped/simplified if a common configuration works for all
relevant targets is selected as defualt</li>
<li>Patch and compule g_dbgp on BBB instead cross-compile</li>
<li>Find a simple way to send debug messages from targets userland</li>
</ol>
</div>
<div class="section">
<p>
Copyright © 2015 Alex David <opdecirkel@gmail.com><br/>
This document is released under the Creative Commons Attribution-ShareAlike 4.0 International Public License and all future versions.
A copy of the license can be found at <a href="../cc-by-sa-4.txt">../cc-by-sa-4.txt</a>.
</p>
<p>
This document is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See <a href="../cc-by-sa-4.txt">../cc-by-sa-4.txt</a> for more information.
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