hid-generic driver

* enable input device driver first. HID depends on it.
kernel menuconfig -> device drivers -> input device supports
- select Generic input layer
kernel menuconfig -> device drivers -> HID support -> HID bus support ->
- select /dev/hidraw raw HID device support
- select Generic HID driver


CONFIG_INPUT=y
CONFIG_HID=y
CONFIG_HIDRAW=y
CONFIG_HID_GENERIC=y

hidraw udev rules

/etc/udev/rules.d/100-hidraw.rules

KERNEL=="hidraw*", SUBSYSTEM=="hidraw", MODE="0664", ATTRS{idVendor}=="1234", ATTRS{idProduct}=="4321", GROUP="plugdev"

linux lsusb

lsusb -vd 2650:1616

echo -n -e '\x66\x6f\x6f' > /dev/hidraw0
echo -n -e \\x66\\x6f\\x6f > /dev/hidraw0


https://www.kernel.org/doc/Documentation/hid/hidraw.txt

libudev to locate hidraw
devices attached to the system.  There is a tutorial on libudev with a
working example at:
 http://www.signal11.us/oss/udev/

write()
--------
The write() function will write a report to the device. For USB devices, if
the device has an INTERRUPT OUT endpoint, the report will be sent on that
endpoint. If it does not, the report will be sent over the control endpoint,
using a SET_REPORT transfer.

The first byte of the buffer passed to write() should be set to the report
number.  If the device does not use numbered reports, the first byte should
be set to 0. The report data itself should begin at the second byte.

http://elixir.free-electrons.com/linux/latest/source/samples/hidraw/hid-example.c

http://www.signal11.us/oss/udev/

$/sys/class/hidraw/hidraw0$ ls
/sys/class/hidraw/hidraw0/device


/sys/bus/usb/devices/2-1.2/

DNS info on Linux

$ nmcli device show eth0

cat /etc/resolv.conf

linux thread stack size

ulimit -s : shows in KB

Set Linux Terminal Console Column Width

* use variable $COLUMNS specifies the wide on terminal session is
 ex) export COLUMNS=100

how to check kernel module address

cat /proc/modules
cat /proc/kallsyms
/sys/module/<MODULE_NAME>/sections/

github download a commit

wget https://github.com/{username}/{project name}/commit/{sha1}.patch

wget https://github.com/ebmajor/my_github_project/commit/4cea0bd9d9151c3036b59e4131c53339b1a0e1f5.patch

openwrt open-wrt

Adding configuration options

If you would like configure your package installation/compilation in the menuconfig you can do the following: Add MENU:=1 to your package definition like this:

define Package/mjpg-streamer
  SECTION:=multimedia
  CATEGORY:=Multimedia
  TITLE:=MJPG-streamer
  DEPENDS:=@!LINUX_2_4 +libpthread-stubs +jpeg
  URL:=http://mjpg-streamer.wiki.sourceforge.net/
  MENU:=1
endef

Create a config key in the Makefile:

define Package/mjpg-streamer/config
 source "$(SOURCE)/Config.in"
endef

Create a Config.in file directory where the Makefile is located with the content like this:

 # Mjpg-streamer configuration
 menu "Configuration"
  depends on PACKAGE_mjpg-streamer

 config MJPEG_STREAMER_AUTOSTART
  bool "Autostart enabled"
  default n

  menu "Input plugins"
   depends on PACKAGE_mjpg-streamer
   config MJPEG_STREAMER_INPUT_FILE
    bool "File input plugin"
    help 
     You can stream pictures from jpg files on the filesystem
    default n
  
   config MJPEG_STREAMER_INPUT_UVC
    bool "UVC input plugin"
    help
     You can stream pictures from an Universal Video Class compatible webcamera
    default y
  
   config MJPEG_STREAMER_FPS
    depends MJPEG_STREAMER_INPUT_UVC
    int "Maximum FPS"
    default 15

   config MJPEG_STREAMER_PICT_HEIGHT
    depends MJPEG_STREAMER_INPUT_UVC
    int "Picture height"
    default 640

   config MJPEG_STREAMER_PICT_WIDTH
    depends MJPEG_STREAMER_INPUT_UVC
    int "Picture width"
    default 480


   config MJPEG_STREAMER_DEVICE
    depends MJPEG_STREAMER_INPUT_UVC
    string "Device"
    default /dev/video0
 
   config MJPEG_STREAMER_INPUT_GSPCA
    bool "GSPCA input plugin"
    help
     You can stream pictures from a gspca supported webcamera Note this module is deprecated, use the UVVC plugin instead
    default n
  endmenu
 
  # ......
 
 endmenu

Above you can see examples for various type config parameters.

And finally you can check your configuration parameters in your Makefile in the following way: (Note that you can reference to the parameters value with it name prefixed with CONFIG_)

ifeq ($(CONFIG_MJPEG_STREAMER_INPUT_UVC),y)
 $(CP) $(PKG_BUILD_DIR)/input_uvc.so $(1)/usr/lib
endif

macbook airport

cd /System/Library/PrivateFrameworks/Apple80211.framework/Versions/Current/Resources
sudo ./airport en0 -I

dump mtd block in linux kernel

uboot$ smem
kernel$ cat /proc/mtd
kernel$ ls -l /dev/
kernel$ hexdump -C /dev/mtdblock7 -s 4096 -n 1024
(offset 4096 == 0x1000, len = 1024)

dd if=/dev/mtdblock7 of=/root/data.bin count=64 bs=1024

dd if=/dev/mtd7 of=/root/data.bin bs=32 count=377 skip=128

bs: block size to read at once
count: number of 'bs' to run
* total size = bs * count = 64KB


* flash erase on kernel
kernel$flash_erase /dev/mtdblock7

* flash copy on kernel
kernel$ flashcp u-boot-env /dev/mtdblock7

trace the linux daemon log (running in background)

tail -F /var/log/messages

android crash report

c:>adb bugreport 2>&1 | tee bugreport.txt
(be patient, it takes time)

hostapd.conf

--- default:: hostapd-etsi-vht80.conf
driver=nl80211
logger_syslog=127
logger_syslog_level=2
logger_stdout=127
logger_stdout_level=2
country_code=DK
ieee80211d=1
ieee80211h=1
hw_mode=a
channel=52

ieee80211n=1
ht_capab=[HT40+][LDPC][SHORT-GI-20][SHORT-GI-40][TX-STBC][RX-STBC1][DSSS_CCK-40]
vht_oper_chwidth=1
vht_oper_centr_freq_seg0_idx=58
ieee80211ac=1
vht_capab=[RXLDPC][SHORT-GI-80][TX-STBC-2BY1][SU-BEAMFORMER][SU-BEAMFORMEE][MU-BEAMFORMER][RX-ANTENNA-PATTERN][TX-ANTENNA-PATTERN][MAX-MPDU-11454][RX-STBC-1][MAX-A-MPDU-LEN-EXP7]

interface=wlan2
ctrl_interface=/var/run/hostapd
disassoc_low_ack=0
preamble=1
wmm_enabled=1
ignore_broadcast_ssid=0
uapsd_advertisement_enabled=1
auth_algs=1
wpa=0
ssid=5G-DFS
bridge=br-lan

***
802.11ac may have one of three lengths: 3,895 bytes, 7,991 bytes, or 11,454 bytes.
but hostapd accept only 7991 and 11454.
[MAX-MPDU-7991]
[MAX-MPDU-11454]

The maximum length of an A-MPDU is controlled by the value of a field called the Maximum A-MPDU Length Exponent, which describes the maximum length of an A-MPDU by the formula
2^(13+Exponent) - 1 bytes.
802.11ac allows values for the exponent ranging from 0 to 7, which allows the maximum A-MPDU length to range from 8 KB to 1 MB.
[MAX-A-MPDU-LEN-EXP7] ~ [MAX-A-MPDU-LEN-EXP1]

android alarm dump

adb shell dumpsys alarm

alarmManager.cancel(pendingIntent) and pendingIntent.cancel()

sharing files on windows among windows, linux, and mac

* using samba protocol
* set-up folder sharing on windows

* on Linux
* install cifs-utils
sudo apt install cifs-utils

* PETER-DESKTOP is to be added to /etc/hosts

* add credential info
----- credential info -----
cat /home/peter/.smbcredentials
username=Peter
password=Password

peter@peter-linux-dell:~$ ls -al .smbcredentials  (root, 0600)
-rw------- 1 root root 187 Oct  3 15:16 .smbcredentials

-------------------------------------------------------------------------------

* add this line to /etc/fstab
----- /etc/fstab -----
//PETER-DESKTOP/shares /home/peter/shares cifs auto,iocharset=utf8,uid=1000,credentials=/home/peter/.smbcredentials,file_mode=0775,dir_mode=0775 0 0

-------------------------------------------------------------------------------

Wi-Fi DFS PRF/PPS to PRi

how to find the location of installed packages (or libraries)

sudo dpkg -L packagename

sudo dpkg -L libnl-3-dev

sudo apt install libnl-genl-3-dev

sudo dpkg -L libnl-genl-3-dev

finding missing header files in ubuntu

sudo apt install apt-file

apt-file update

apt-file search netlink/genl/genl.h

libnl-3-dev: /usr/include/libnl3/netlink/genl/genl.h

sudo apt-get install libnl-3-dev

batch renaming files in linux

sudo apt install mmv

mmv "*.patch" "c00-#1.patch"

c programming variables' memory location check

gcc -O0 memory.c -Wl,-Map=output.map

memory map of memory sections

https://www.ele.uva.es/~jesus/hardware_empotrado/Compiler.pdf

sparse build check

https://kernelnewbies.org/Sparse

sudo apt-get install sparse

How to use sparse

Choose a subdirectory in the kernel tree that you want to check for sparse warnings and errors, for instance that could be drivers/staging/wlan-ng, and do:

$ make C=2 drivers/staging/wlan-ng/

You can use the variable CF to pass more checkflags to sparse. For example, you can enable endian checks doing:

$ make C=2 CF="-D__CHECK_ENDIAN__" drivers/staging/wlan-ng/

The warnings produced indicate sites in code where types relevant to byteorder are mixed, possibly leading to buggy behavior.

You can observe what are the default checkflags set in the Makefile. You will see something close to the following:

CHECKFLAGS     := -D__linux__ -Dlinux -D__STDC__ -Dunix -D__unix__ \
                  -Wbitwise -Wno-return-void $(CF)

http://jake.dothome.co.kr/sparse/


* smatch ??
http://smatch.sourceforge.net/
http://events.linuxfoundation.org/sites/events/files/slides/Static%20code%20checking.pdf

802.11ac Max. length of A-MPDU

Maximum A-MPDU Length Exponent

Indicates the maximum length of A-MPDU that the STA can receive.
EOF padding is not included in this limit.

This field is an integer in the range of 0 to 7.
The length defined by this field is equal to
2 ^(13 + Maximum A-MPDU Length Exponent) – 1 octets.


Following are some of the useful attributes of 11ac MAC layer.
•  MSDU size for MAC payload - 2304
•  MPDU size for MAC frame - 11,454
•  PSDU size(PLCP payload) - About 4MB
•  PPDU size(PLCP frame) - 5.484 ms

hostapd.conf

MAX-A-MPDU-LEN-EXP1 ~ MAX-A-MPDU-LEN-EXP7
MAX-MPDU-7991 or MAX-MPDU-11454

bash shell infinite loop example

https://www.cyberciti.biz/faq/bash-infinite-loop/

iperf TOS option

CLIENT SPECIFIC OPTIONS

-S, --tos N               set the IP 'type of service'

The type-of-service for outgoing packets. (Many routers ignore the TOS field.)
You may specify the value in hex with a '0x' prefix, in octal with a '0' prefix, or in decimal.
For example, '0x10' hex = '020' octal = '16' decimal.
The TOS numbers specified in RFC 1349 are:

    IPTOS_LOWDELAY     minimize delay        0x10
    IPTOS_THROUGHPUT   maximize throughput   0x08
    IPTOS_RELIABILITY  maximize reliability  0x04
    IPTOS_LOWCOST      minimize cost         0x02

   0     1      2       3       4       5       6       7
+-----+-----+-----+-----+-----+-----+-----+-----+
 |   PRE               |                                   |  M   |
 |   CEDENCE    |           TOS                 |  B   |
 |                          |                                   |  Z   |
+-----+-----+-----+-----+-----+-----+-----+-----+

"PRECEDENCE" is intended to denote the importance or priority of the datagram.

The last field, labeled "MBZ" (for "must be zero") above, is currently unused.

1000   --   minimize delay ( + MBZ (0) = 1000 0 = 1 0000 = 0x10)
0100   --   maximize throughput ( + MBZ (0) = 0100 0 = 0 1000 = 0x08)
0010   --   maximize reliability ( + MBZ (0) = 0010 0 = 0 0100 = 0x04)
0001   --   minimize monetary cost ( + MBZ (0) = 0001 0 = 0 0010 = 0x02)
0000   --   normal service ( + MBZ (0) = 0000 0 = 0 0000 = 0x00)
* bit 3: minimize delay, bit 4: maximize throughput, bit 5: maximize reliability

PRECEDENCE
000 Routine
001 Priority
010 Immediate
011 Flash
100 FlashOverride
101 Critical
110 InterNetwork Control
111 Network Control


A. DOD DD173 Precedence/Priority Filed Explanations (Lowest-Highest):

Routine: (R) “…is used for all messages that justify transmission by electrical means unless the message delivery is of sufficient urgency to require higher precedence.”
Priority: (P) “…is used for all messages that require expeditious action by the addressee(s) and/or furnish essential information for the conduct of ongoing operations.”
Immediate (O) “…is reserved for messages relating to situations that gravely affect the security of National/Allied forces or populace.”
Flash (Z) “…is reserved for initial enemy contact messages or operational combat messages of extreme urgency.”
Flash Override (X) “… is reserved for messages relating to the outbreak of hostilities and/or detonation of nuclear devices.”
CRITIC/ECP “…stands for “Critical and Emergency Call Processing” and should only be used for authorized emergency communications, for example in the United States Government Emergency Telecommunications Service (GETS), the United Kingdom Government Telephone Preference Scheme (GTPS) and similar government emergency preparedness or reactionary implementations elsewhere.”
1. Network Control “…is intended to be used within a network only. The actual use and control of that designation is up to each network.”

2. Internetwork Control “…is intended for use by gateway control originators only.”

TOS (Dec)	TOS (Hex)	TOS (Bin)	TOS Precedence (Bin)	TOS Precedence (Dec)	TOS Precedence Name	TOS Delay flag	TOS Throughput flag	TOS Reliability flag	DSCP (Bin)	DSCP (Hex)	DSCP (Dec)	DSCP/PHB Class
0	0x00	00000000	000	0	Routine	0	0	0	000000	0x00	0	none
4	0x04	00000100	000	0	Routine	0	0	1	000001	0x01	1	none
8	0x08	00001000	000	0	Routine	0	1	0	000010	0x02	2	none
12	0x0C	00001100	000	0	Routine	0	1	1	000011	0x03	3	none
16	0x10	00010000	000	0	Routine	1	0	0	000100	0x04	4	none
32	0x20	00100000	001	1	Priority	0	0	0	001000	0x08	8	cs1
40	0x28	00101000	001	1	Priority	0	1	0	001010	0x0A	10	af11
48	0x30	00110000	001	1	Priority	1	0	0	001100	0x0C	12	af12
56	0x38	00111000	001	1	Priority	1	1	0	001110	0x0E	14	af13
64	0x40	01000000	010	2	Immediate	0	0	0	010000	0x10	16	cs2
72	0x48	01001000	010	2	Immediate	0	1	0	010010	0x12	18	af21
80	0x50	01010000	010	2	Immediate	1	0	0	010100	0x14	20	af22
88	0x58	01011000	010	2	Immediate	1	1	0	010110	0x16	22	af23
96	0x60	01100000	011	3	Flash	0	0	0	011000	0x18	24	cs3
104	0x68	01101000	011	3	Flash	0	1	0	011010	0x1A	26	af31
112	0x70	01110000	011	3	Flash	1	0	0	011100	0x1C	28	af32
120	0x78	01111000	011	3	Flash	1	1	0	011110	0x1E	30	af33
128	0x80	10000000	100	4	FlashOverride	0	0	0	100000	0x20	32	cs4
136	0x88	10001000	100	4	FlashOverride	0	1	0	100010	0x22	34	af41
144	0x90	10010000	100	4	FlashOverride	1	0	0	100100	0x24	36	af42
152	0x98	10011000	100	4	FlashOverride	1	1	0	100110	0x26	38	af43
160	0xA0	10100000	101	5	Critical	0	0	0	101000	0x28	40	cs5
176	0xB0	10110000	101	5	Critical	1	0	0	101100	0x2C	44	voice-admit
184	0xB8	10111000	101	5	Critical	1	1	0	101110	0x2E	46	ef
192	0xC0	11000000	110	6	InterNetwork Control	0	0	0	110000	0x30	48	cs6
224	0xE0	11100000	111	7	Network Control	0	0	0	111000	0x38	56	cs7