Print a Range of a char Array without a for Loop

Code:

#include <stdio.h> 

 int main() 

{ 

   char a[1024] = "abcdefghijklmnopqrstuvwxyz";  

   printf("Characters 0 through 2 of a[]: %.3s\n", a); 

   printf("Characters 10 through 15 of a[]: %.6s\n", &a[10]); return 0; 

}

Prints this:
Characters 0 through 2 of a[]: abc 

Characters 10 through 15 of a[]: klmnop

The "%.Ns" notation in the printf string is "%s" with a precision specifier. It's buried in the geek-speak in the printf(3) man page


ref:
https://www.linuxquestions.org/questions/programming-9/is-there-a-way-to-print-a-range-of-a-char-array-without-a-for-loop-842798/

Arduino Command Line Usage

arduino is simply a program from your installation directory. Without any parameters, it would just start the Arduino IDE.

open ~/.bashrc and add the following line at the bottom:

              PATH=$PATH:/home/aaa/xxx/yyy/arduinoIDE/arduino-1.8.2

Now we can use cmd "arduino" everywhere.

Use cases:

For arduino nano:

arduino --board arduino:avr:nano:cpu=atmega328 --port /dev/ttyUSB0 --upload beep.ino

Serial Monitor:
picocom /dev/ttyUSB0 -b 9600

ref:
https://unix.stackexchange.com/questions/26047/how-to-correctly-add-a-path-to-path
https://github.com/arduino/Arduino/blob/master/build/shared/manpage.adoc

I think the following problems are the same:

Problem 1:
E: Could not get lock /var/lib/dpkg/lock - open (11: Resource temporarily unavailable)
E: Unable to lock the administration directory (/var/lib/dpkg/), is another process using it?

Problem  2:

sudo apt-get -f install

Reading package lists... Done

Building dependency tree       

Reading state information... Done

0 upgraded, 0 newly installed, 0 to remove and 39 not upgraded.

5 not fully installed or removed.

After this operation, 0 B of additional disk space will be used.

Setting up linux-image-extra-4.4.0-104-generic (4.4.0-104.127) ...

run-parts: executing /etc/kernel/postinst.d/apt-auto-removal 4.4.0-104-generic /boot/vmlinuz-4.4.0-104-generic

run-parts: executing /etc/kernel/postinst.d/initramfs-tools 4.4.0-104-generic /boot/vmlinuz-4.4.0-104-generic

update-initramfs: Generating /boot/initrd.img-4.4.0-104-generic

gzip: stdout: No space left on device

E: mkinitramfs failure cpio 141 gzip 1

update-initramfs: failed for /boot/initrd.img-4.4.0-104-generic with 1.

run-parts: /etc/kernel/postinst.d/initramfs-tools exited with return code 1

dpkg: error processing package linux-image-extra-4.4.0-104-generic (--configure):

 subprocess installed post-installation script returned error exit status 1

dpkg: dependency problems prevent configuration of linux-image-generic:

 linux-image-generic depends on linux-image-extra-4.4.0-104-generic; however:

  Package linux-image-extra-4.4.0-104-generic is not configured yet.

dpkg: error processing package linux-image-generic (--configure):

 dependency problems - leaving unconfigured

dpkg: dependency problems prevent configuration of linux-generic:

 linux-generic depends on linux-image-generic (= 4.4.0.104.109); however:

  Package linux-image-generic is not configured yet.

dpkg: error processing package linux-generic (--configure):

 dependency problems - leaving unconfigured

Setting up linux-image-4.4.0-98-generic (4.4.0-98.121) ...

No apport report written because the error message indicates its a followup error from a previous failure.

                                                                                                          No apport report written because the error message indicates its a followup error from a previous failure.

                                                                             Running depmod.

update-initramfs: deferring update (hook will be called later)

The link /initrd.img is a dangling linkto /boot/initrd.img-4.4.0-98-generic

vmlinuz(/boot/vmlinuz-4.4.0-98-generic

) points to /boot/vmlinuz-4.4.0-98-generic

 (/boot/vmlinuz-4.4.0-98-generic) -- doing nothing at /var/lib/dpkg/info/linux-image-4.4.0-98-generic.postinst line 491.

Examining /etc/kernel/postinst.d.

run-parts: executing /etc/kernel/postinst.d/apt-auto-removal 4.4.0-98-generic /boot/vmlinuz-4.4.0-98-generic

run-parts: executing /etc/kernel/postinst.d/initramfs-tools 4.4.0-98-generic /boot/vmlinuz-4.4.0-98-generic

update-initramfs: Generating /boot/initrd.img-4.4.0-98-generic

gzip: stdout: No space left on device

E: mkinitramfs failure cpio 141 gzip 1

update-initramfs: failed for /boot/initrd.img-4.4.0-98-generic with 1.

run-parts: /etc/kernel/postinst.d/initramfs-tools exited with return code 1

Failed to process /etc/kernel/postinst.d at /var/lib/dpkg/info/linux-image-4.4.0-98-generic.postinst line 1052.

dpkg: error processing package linux-image-4.4.0-98-generic (--configure):

 subprocess installed post-installation script returned error exit status 2

No apport report written because MaxReports is reached already

                                                              dpkg: dependency problems prevent configuration of linux-image-extra-4.4.0-98-generic:

 linux-image-extra-4.4.0-98-generic depends on linux-image-4.4.0-98-generic; however:

  Package linux-image-4.4.0-98-generic is not configured yet.

dpkg: error processing package linux-image-extra-4.4.0-98-generic (--configure):

 dependency problems - leaving unconfigured

No apport report written because MaxReports is reached already

                                                              Errors were encountered while processing:

 linux-image-extra-4.4.0-104-generic

 linux-image-generic

 linux-generic

 linux-image-4.4.0-98-generic

 linux-image-extra-4.4.0-98-generic

E: Sub-process /usr/bin/dpkg returned an error code (1)

Problem  3:

The volume "boot" has only  bytes disk space remaining

//////////////////////////////////////////////////////////////////////////////////////////////////////////////////

Solution:

Step 1:

List all the current existing kernels.

ls /boot/ | grep vmlinuz

vmlinuz-4.4.0-104-generic

vmlinuz-4.4.0-97-generic

vmlinuz-4.4.0-98-generic

Step 2:

Find the current kernel in use.

uname -r

4.4.0-97-generic

Step 3:

Remove one of them not in use:

sudo apt-get purge linux-image-4.4.0-104-generic

Reading package lists... Done

Building dependency tree       

Reading state information... Done

The following packages were automatically installed and are no longer required:

  linux-headers-4.4.0-104 linux-headers-4.4.0-104-generic linux-headers-generic thermald

Use 'sudo apt autoremove' to remove them.

0 upgraded, 0 newly installed, 0 to remove and 39 not upgraded.

ref:
https://askubuntu.com/questions/218783/the-volume-boot-has-only-0-bytes-disk-space-remaining

Toubleshooting: ampy "could not enter raw repl" error

When using ampy tool, nothing works!

ampy --port /dev/ttyUSB0 get boot.py

>>> 
Traceback (most recent call last):
  File "/usr/local/bin/ampy", line 11, in <module>
    sys.exit(cli())
  File "/usr/local/lib/python2.7/dist-packages/click/core.py", line 722, in __call__
    return self.main(*args, **kwargs)
  File "/usr/local/lib/python2.7/dist-packages/click/core.py", line 697, in main
    rv = self.invoke(ctx)
  File "/usr/local/lib/python2.7/dist-packages/click/core.py", line 1066, in invoke
    return _process_result(sub_ctx.command.invoke(sub_ctx))
  File "/usr/local/lib/python2.7/dist-packages/click/core.py", line 895, in invoke
    return ctx.invoke(self.callback, **ctx.params)
  File "/usr/local/lib/python2.7/dist-packages/click/core.py", line 535, in invoke
    return callback(*args, **kwargs)
  File "/usr/local/lib/python2.7/dist-packages/ampy/cli.py", line 96, in get
    contents = board_files.get(remote_file)
  File "/usr/local/lib/python2.7/dist-packages/ampy/files.py", line 68, in get
    self._pyboard.enter_raw_repl()
  File "/usr/local/lib/python2.7/dist-packages/ampy/pyboard.py", line 184, in enter_raw_repl
    raise PyboardError('could not enter raw repl')
ampy.pyboard.PyboardError: could not enter raw repl

On the NodeMCU side it prints:

...

>>>
>raw REPL; CTRL-B to exit >

The reason is because the serial port is busy. So after I closed the REPL python terminal and called ampy again, every thing works perfectly. 

ref:

http://forums.openmv.io/viewtopic.php?t=298

Casting Bitwise struct to Integer

I have bitwise structure with a bunch of flags.

struct {

  uint8_t a: 4; 

  uint8_t b: 4; 

} _tVarA

_tVarA Var_A = {0,0};

But when I want to view them as a whole integer, I need to cast it like this:

                               *(uint8_t*)&Var_A

ref:
http://www.avrfreaks.net/forum/casting-bitfield-struct-integer
https://stackoverflow.com/questions/11903820/casting-struct-into-int

Programming ESP8266 (01) using FTDI and Arduino IDE

ESP8266 is essentially a microcontroller. We can do development to it from the Arduino IDE.

Step 1: Install the ESP8266 board in Arduino IDE

According to the first method from https://github.com/esp8266/Arduino

(1) Start Arduino and open Preferences window.
(2) Enter http://arduino.esp8266.com/stable/package_esp8266com_index.json into Additional Board Manager URLsfield. You can add multiple URLs, separating them with commas.
(3) Open Boards Manager from Tools > Board menu and install esp8266 platform (and don't forget to select your ESP8266 board from Tools > Board menu after installation).

Step 2: Wiring

The Wiring is 90% the same from my last post: Getting Started with esp8266-01 as shown below:

The only thing different is that we must connect GND from FTDI to GPIO0 on ESP8266. This is to set the ESP8266 into "bootloading" mode. RST and GPIO2 pins can be left floating.

Step 3: Coding
If the board is chosen from Tool > Board as General ESP8266, we can just pull the blinky example from File > examples.


Step 4: Flash the Module

Flash the board using the following parameters.

/////////////////////////////////////////////////////////////////////////////////////////////

Troubleshooting:
(1)
At first I got the following error message:

warning: espcomm_sync failed
error: espcomm_open failed
error: espcomm_upload_mem failed
error: espcomm_upload_mem failed

Checked online and find some hints. The cause can be one of two things:

(1) Insufficient power. Try to power the ESP8266 from an external 3.3V power supply such as a lab supply. Two fully charged AA batteries should do the trick too. Make sure your serial adapter's GND pin is also connected to the ESP's GND pin in order to provide a common ground.

(2) ESP8266 is not in programming mode. Make sure GPIO0 is attached to GND and turn the ESP off and on again. It will then boot into programming mode. Once programmed, you can take it off GND.
So here is what I did:

> unplug the GND <=> GPIO0
basically go back the the getting start with ESP8266 post and do "AT" command and got "OK".

> plug the GND <=> GPIO0 back again
Flash and it worked!! You can see the blue led blinking.


(2)
Next day, I plug in the ftdi and the blue is NOT blinking any more. We must put it back to normal mode by unplug the GPIO0 from GND.


ref:
https://www.monocilindro.com/2017/02/25/flashing-esp8266-using-ftdi-and-arduino-ide/
https://github.com/esp8266/Arduino
https://stackoverflow.com/questions/31371969/cannot-program-esp8266

Getting Started with the ESP8266 (01)

Step 1: Wiring

I got a ESP-01 version of this module, which has 8 pins: VCC, GND, CH_PD, TX, RX, RST, GPIO0, and GPIO1. Wiring the module is not complicated and should be the same for all versions of this module:

• VCC needs 3.3V
• CH_PD has to be pulled-up (meaning it has to be connected to 3.3V as well)
• GND is connected to FTDI’s GND pin
• RX is connected to FTDI’s TX pin, because you want to create a loop: RX-> TX => RX -> TX
• TX is connected to FTDI’s RX pin
• other pins are left floating

VERY VERY IMPORTANTLY, this module needs 3.3V, not 5V which is what most FTDIs supply. Even if your FTDI module has an 3.3V output or a switch to change the voltage, please measure it with a multimeter to make sure it is outputing 3.3V exactly. I wasted more than one hour just because I trusted the piece of garbage!!!!

Step 2: Communication

Open the serial monitor from Arduino IDE, change the two settings at the right bottom corner according to the above picture. As you can see, my first 3 AT command didn't go through because of the carriage return is not there.


ref:
http://williamdurand.fr/2015/03/17/playing-with-a-esp8266-wifi-module/
http://rancidbacon.com/files/kiwicon8/ESP8266_WiFi_Module_Quick_Start_Guide_v_1.0.4.pdf
http://www.instructables.com/id/Getting-Started-With-the-ESP8266-ESP-01/

STATIC Variables and Functions in C

ref:
http://www.jianshu.com/p/f413ba3b2728
http://www.cnblogs.com/wly603/archive/2012/04/11/2442065.html
http://bbs.csdn.net/topics/350238100
http://www.cppblog.com/dbkong/archive/2006/12/09/16169.html

Build MicroPython Firmware for ESP8266

ref:
https://learn.adafruit.com/building-and-running-micropython-on-the-esp8266/build-firmware
https://github.com/micropython/micropython/wiki/Getting-Started