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Published: Friday, 18 January 2019 14:18

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yosys - open source synthesis tool

Yosys is oen source synthesis tool. You provide it an RTL, and it spits out optimized gate level netlist.

yosys details are on this link: http://www.clifford.at/yosys/about.html

yosys download and installation. I'll show steps for both debian based OS (as Linux Mint or Ubuntu) and Fedora based OS (as CentOS). I haven't gotten to installing Yosys on LinuxMint, so will provide instructions for it later.

A CentOS: I will show steps for yosys installation on CentOS 7.5 1804 distro.

1. download python3 => see instructions for downloading python3 on python page. Do these steps:

•  I. First do "sudo yum install epel-release".
•  II. Next do "sudo yum install python3.4"
•  III. sudo curl -O https://bootstrap.pypa.io/get-pip.py
•  IV. sudo /usr/bin/python3.4 get-pip.py

2. download tcl/tk => see instructions for downloading tcl/tk in tcl/tk page. Use manual download and install from tcl8.7a

3. download libffi => run "sudo yum install libffi libffi-devel". Run "locate libffi" This will show libffi.so lib in /usr/lib64 and docs in /usr/share/doc. ffi.h file will be in /usr/include/libffi.h

4. install readline => sudo yum install readline-devel. This creates /usr/include/readline/readline.h

5. Now download yosys from here: http://www.clifford.at/yosys/download.html. Steps below:

 A. download yosys-0.8.tar.gz. Extract it within the file windows manager using right click and choosing "extract". That will create another dir named "yosys-yosys-0.8"

 B. type "make config-gcc". This will create Makefile with gcc as the compiler. this will suffice, as gcc can compile C++ also. There is no need to install clang.

 C. type "make" => this will start compilation process using gcc (should show CONFIG := gcc from Makefile.conf). Possible Errors:

• tcl.h not found (called in kernel/yosys.h) => tclsh not installed or found. See bullet 2 above.
• tclsh command not found => If you see this error and tclsh is alrready installed, probably the link or path for tclsh is not correct.
• readline/readline.h not found (called in kernel/driver.cc) => readline not installed. See bullet 4 above.
• ffi.h not found (called in frontends/ast/dpicall.cc) => libffl not installed. See bullet 3 above.

     If no errors found, we should see 100% build for yosys, then it downloads "abc" from berkeley, does 95% build for abc binary, and then finally "Build successful" message.

7. make test => runs all tests. Needs icarus verilog or "icarus"

8. sudo make install => This is final step where it just puts binaries for yosys in /usr/local/bin/yosys. Other yosys related binaries also here.

9. Now running yosys (typing yosys or /usr/local/bin/yosys) should bring up yosys tool. However, if we get "error while loading shared libraries: libtcl8.7.so: cannot open shared object file: No such file or directory" , that means LD_LIBRARY_PATH var is not set.   If we find "libtcl8.7.so", we see it in /usr/local/lib/libtcl.8.7.so". "echo $LD_LIBRARY_PATH" shows blank. For bash shell, type "LD_LIBRARY_PATH=$LD_LIBRARY_PATH:/usr/local/lib/". Now, "echo $LD_LIBRARY_PATH" will show ":/usr/local/lib/". Type "export LD_LIBRARY_PATH". Now typing yosys brings up cmd line yosys tool. To make this change permanent, add this line in ~/.bashrc (assuming you are using bash)

• export LD_LIBRARY_PATH=$LD_LIBRARY_PATH:/usr/local/lib/

10. Install open src s/w graphviz for graphical viewing: sudo yum install graphviz => installs graphviz-2.30*

10. All yosys cmds and scripts available on yosys webpage.

yosys usage:

 1. Read Yosys manual which explains everything in very good detail. http://www.clifford.at/yosys/files/yosys_manual.pdf

Yosys example: TO DO ---

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Published: Tuesday, 08 January 2019 05:24

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 Setting internet server:

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Published: Wednesday, 05 December 2018 20:45

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Riddles/puzzles:

1. Transport problem: There is a lion, cow and heap of grass. All 3 need to be transported from 1 side of river to other side on a boat. The boatman is rowing the boat, and he can only carry 1 of the 3 at one time, otherwise the boat will drown. Lion can eat cow, while cow can eat grass. Lion doesn't eat grass. How can the boatman transport all 3 of them across the river, without any of them eating anyone else. He can make as many trips as he wants. The only problem is that as soon as the boatman disappears from the scene, the animals are free to eat their food. So, if he leaves lion and cow while carrying grass with him, lion can eat cow. Since boatman cannot carry more than 1 of them with him, he has to leave 2 of them together, but in such a combination that no one can eat the other.

Soln: carry cow in 1st trip and leave it on other side of river. Then come back empty and carry lion with him. Then leave lion on other side, but bring back cow with him, else lion will eat cow. On his third trip, leave cow on the bank of river, and carry grass with him, and leave it on other side. Then come back empty, and carry cow with him to other side. Then all 3 animals end up on other side.

2. Switch problem: You have seen light switches in house. Sometimes we see the same light bulb being controlled by 2 switches. i.e light in the bedroom being controlled by the switch at entrance of bedroom, while also being controlled by switch by the side of bed. Draw a connection diagram showing how it works. We will need 3 way switch for these, not the regular 2 way switch. Also, how can you control the light bulb with "n" switches. We will need 4 way switches to make this work.

3. Bulb Problem: 3 incandescent bulbs in a closed room, 3 switches outside the room. All switches are in off state to start with, so all light bulbs are off. How can you figure out which light bulb is controlled by which switch. You are allowed to turn switches on/off as many times as you want, but once you enter the room, you are not allowed to go outside the room and flip switches again.

4. monty hall problem: Suppose you're on a game show, and you're given the choice of three doors: Behind one door is a car; behind the others, goats. You pick a door, say No. 1, and the host, who knows what's behind the doors, opens another door, say No. 3, which has a goat. He then says to you, "Do you want to pick door No. 2?" Is it to your advantage to switch your choice? 

5. Hardest Logic puzzle: Logic puzzles are yes/no questions to derive an answer. Link to Hardest Logic Puzzle => https://en.wikipedia.org/wiki/The_Hardest_Logic_Puzzle_Ever

• A simpler version of this puzzle for kids is as follows (the answer is in link above) => You are standing before two doors. One of the path leads to heaven and the other one leads to hell. There are two guardians, one by each door. You know one of them always tells the truth and the other always lies, but you don’t know who is the honest one and who is the liar. You can only ask one question to one of them in order to find the way to heaven. What is the question?

Kids Maths:

1. If there are 4 apples and you take away 3, how many do you have? => 3, because you took 3

2. What occurs twice in a week, once in a year but never in a day? => letter e

3. What goes up and doesn’t come back down?

4. What has two hands but no legs? => clock

5. What’s the easiest way to double your money? => in front of mirror

6. Which month has 28 days? => all of them

7. If four men can build four tables in four hours, how many tables can eight men build in eight hours? =>

8. Three guys rent a hotel room for the night. When they get to the hotel they pay the $30 fee, then go up to their room. Soon the bellhop brings up their bags and gives the lawyers back $5 because the hotel was having a special discount that weekend. So the three lawyers decide to each keep one of the $5 dollars and to give the bellhop a $2 tip. However, when they sat down to tally up their expenses for the weekend the could not explain the following details:
Each one of them had originally paid $10 (towards the initial $30), then each got back $1 which meant that they each paid $9. Then they gave the bellhop a $2 tip. HOWEVER, 3 • $9 + $2 = $29
The guys couldn't figure out what happened to the other dollar. After all, the three paid out $30 but could only account for $29. Can you determine what happened?

9. What digit is the most frequent between the numbers 1 and 1,000 (inclusive)? To solve this riddle you don't want to manually do all of the math but rather try to figure out a pattern.

10. How can you add eight 8's to get the number 1,000? (only use addition) => 888+88+8+8+8

11. Jammy is a milkman. He has 3-liter and 5-liter milk cans. Now, he want to measure 4 liters from these milk cans. How can he do it? =>

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Published: Wednesday, 05 December 2018 04:06

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Linux Directory structure:

tldp website is very good resource for learning Linux. This pdf is very detailed about Linux dir:

https://www.tldp.org/LDP/Linux-Filesystem-Hierarchy/Linux-Filesystem-Hierarchy.pdf

Below info is copied from here: https://www.howtogeek.com/117435/htg-explains-the-linux-directory-structure-explained/

/ => Everything on your Linux system is located under the / directory, known as the root directory.

Under root dir, we have these other subdir:

• /bin => The /bin directory contains the essential user binaries (programs) that must be present when the system is mounted in single-user mode. Applications such as Firefox are stored in /usr/bin, while important system programs and utilities such as the bash shell are located in /bin. The /usr directory may be stored on another partition – placing these files in the /bin directory ensures the system will have these important utilities even if no other file systems are mounted. The /sbin directory is similar – it contains essential system administration binaries.
• /sbin => The /sbin directory is similar to the /bin directory. It contains essential binaries that are generally intended to be run by the root user for system administration.
• /lib => The /lib directory contains libraries needed by the essential binaries in the /bin and /sbin folder. Libraries needed by the binaries in the /usr/bin folder are located in /usr/lib.
• /lib64 => The /lib64 contains 64 bit lib.

In CentOS, /bin, /sbin, /lib and /lib64 are all soft links to corresponding dir in /usr dir. So, all these dir are actually in /usr dir. eg. bin -> usr/bin (so when we do /bin, it's actually /usr/bin)

Modules: /lib/modules/<kernel-version>/ dir has all compiled drivers (aka kernel modules). Inside it is kernel/drivers/ subdir which has modules for wireless device, bluetooth device, usb device, etc.

lsmod => list all loaded modules

modinfo <module_name> => This gives detailed info about any of the modules that you got from lsmod.

i.e modinfo video => shows location of compiled kernel module (in /lib/modules/.../*.ko), and other info.

modprobe => useful cmd for loading or unloading modules

Linux directories;

• /boot => The /boot directory contains the files needed to boot the system – for example, the GRUB boot loader’s files (in grub2 dir) and your Linux kernels (file vmliinuz*) are stored here. The boot loader’s configuration files aren’t located here, though – they’re in /etc with the other configuration files. They generate grub.cfg file in grub2 dir as explained in section below. /boot dir has very few files: inintramfs*, vmlinuz*, grub2 dir. initramfs* is the initial RAM file system. It is the 1st root file system that the m/c has access to. It is used for mounting the real rootfs which has all your data. This is introduced from Linux 2.6 kernel series, and serves same purpose as initrd.
• /usr => The /usr directory contains applications and files used by users, as opposed to applications and files used by the system. For example, non-essential applications are located inside the /usr/bin directory instead of the /bin directory and non-essential system administration binaries are located in the /usr/sbin directory instead of the /sbin directory. Libraries for each are located inside the /usr/lib directory. The /usr directory also contains other directories – for example, architecture-independent files like graphics are located in /usr/share.
  • The /usr/local directory is where locally compiled applications install to by default – this prevents them from mucking up the rest of the system.
  • The /usr/src/ dir has src code for linux kernels inside "kernels" subdir. /usr/src/kernels/ has further subdir with Linux kernel version number (i.e: 3.10....x86-64). All linux src files along with Makefile are inside that dir.
• /var => variable data dir. The /var directory is the writable counterpart to the /usr directory (/usr dir is read-only in normal operation). Log files and everything else that would normally be written to /usr during normal operation are written to the /var directory. For example, you’ll find log files in /var/log
• /home => The /home directory contains a home folder for each user. For example, if your user name is bob, you have a home folder located at /home/bob. This home folder contains the user’s data files and user-specific configuration files. Each user only has write access to their own home folder and must obtain elevated permissions (become the root user) to modify other files on the system. ~ refers to the home dir of currently logged in user. So, if alex is logged in, then ~ refers to /home/alex. Each ~ dir conatins hidden files starting with ".", such as .bashrc, .emacs, etc. These files are configuration files that determine the look, feel or startup behaviour of bash, emacs or any other application for that user.
• /etc => The /etc directory contains configuration files, which can generally be edited by hand in a text editor. Note that the /etc/ directory contains system-wide configuration files (/etc/bashrc, /etc/profile) – user-specific configuration files are located in each user’s home directory (eg: /home/bob/.bashrc).
• /root => The /root directory is the home directory of the root user. Instead of being located at /home/root, it’s located at /root. This is distinct from /, which is the system root directory.
• /dev => Linux exposes devices as files, and the /dev directory contains a number of special files that represent devices. These are not actual files as we know them, but they appear as files – for example, /dev/sda represents the first SATA drive in the system. If you wanted to partition it, you could start a partition editor and tell it to edit /dev/sda.
• This directory also contains pseudo-devices, which are virtual devices that don’t actually correspond to hardware. For example, /dev/random produces random numbers. /dev/null is a special device that produces no output and automatically discards all input – when you pipe the output of a command to /dev/null, you discard it.
• /proc => The /proc directory similar to the /dev directory because it doesn’t contain standard files. It contains special files that represent system and process information.
• /media => The /media directory contains subdirectories where removable media devices inserted into the computer are mounted. For example, when you insert a CD into your Linux system, a directory will automatically be created inside the /media directory. You can access the contents of the CD inside this directory.
• /mnt => Historically speaking, the /mnt directory is where system administrators mounted temporary file systems while using them. For example, if you’re mounting a Windows partition to perform some file recovery operations, you might mount it at /mnt/windows. However, you can mount other file systems anywhere on the system.
• /tmp => Applications store temporary files in the /tmp directory. These files are generally deleted whenever your system is restarted and may be deleted at any time by utilities such as tmpwatch.
• /opt => The /opt directory contains subdirectories for optional software packages. It’s commonly used by proprietary software that doesn’t obey the standard file system hierarchy – for example, a proprietary program might dump its files in /opt/application when you install it.
• /lost+found => Each Linux file system has a lost+found directory. If the file system crashes, a file system check will be performed at next boot. Any corrupted files found will be placed in the lost+found directory, so you can attempt to recover as much data as possible.

Dir Permissions:

Every file on linux has permissions defined for 3 different owners - user, group and all others. User is the one who created the file, group is the group of the user to which he belongs, and others refers to all the other users. Each of these 3 owners have read, write and execute (rwx) permissions specified. You will see the user name and group name, as well as rwx permissions of each file when we run cmd:

ls -al file1

-rw-r--r-x. 1 user1 grp1 0 Feb 26 07:08 file1 => user "user1" in group "grp1". permissions are rw for user1, r for grp1 and rx for others.

groups are assigned based on 1st process that runs as login shell (it's run by login pgm in /bin/login). This login pgm runs as root, and calls a C function called initgroups to set up your groups (by reading /etc/group). Each line in /etc/group file has group_name:password:group_id(GID):Group_list(all users who are members of this group). ex: root:x:0: ...  grp1:x:1000:user1. NOTE: root has User id (UID) of 0, group id (GID) of 0. You will see a lot of other groups besides root, and username groups. Those groups are used by system processes. Once your groups are set, any processes run by you inherit those groups.

GRUB:

In linux mint,

/etc/default/grub => has GRUB bootloader related settings. HEre we can choose which OS to boot into by default, how many seconds the boot screen remains up, etc.

/boot/grub/grub.cfg => This is the final file that is automatically generated when grub-mkconfig is run. It uses templates from /etc/grub.d and settings from /etc/default/grub

To change default OS in grub:

1. In Linux mint, open a terminal and login as root. This can be done by typing " su -" to become root user.

2. Change value of GRUB_DEFAULT from 0 to 2 (or whatever number windows loaded is listed at, numbers start from 0 for 1st entry, and so on) in /etc/default/grub.

3. Now run "update-grub". This will update file /boot/grub/grub.cfg. Now, restart your computer and asterisk will appear infront of "windows" in the boot menu, indicating that's the default OS.