Compare PowerPC and ARM Architecture

The end of the year is approaching, but I’d like to have one last delta before taking some time off. PowerPC vs. Arm, seems like an appropriate stand-off. In this rendition. However, I will incarnate the e200z0 core and the Cortex-M4 core, which are the MCU implementations of each corresponding ISAs. For the sake of simplicity, each time the word PowerPC is uttered, I am referring to the e200z0 core; similarly, Arm will stand as a simplification of Cortex-M4.

Getting the obvious out of the way

PowerPC is sold both as silicon (i.e. MCU) as well as synthesizable IP blocks; Arm only sells IP, but there are a number of companies that sell microcontrollers built around said IP. At the end of the day, both cores cannot be compared in terms of technology node because their implementation depends on a third party. I will say, however, that PowerPCs are typically used in automotive and industrial applications which tend to use more robust technology nodes than consumer applications where Arm is typically found. I suspect, but cannot confirm, that one of the reasons for this is that the Arm core is relatively big (physically), and really benefits from a smaller node. Therefore, it is not strange to find PowerPC devices qualified at -40 – 125C ranges, in LPDF packages; Arm devices are normally only qualified in 0 – 85C ranges and come in smaller, BGA packages.

Architecture

Similarly colored boxes show the equivalent blocks for each architecture. It should be immediately obvious that the Cortex-M4 to the left has a significant number of blocks without equivalent on the e200z0 architecture.

And this is what I’d like to talk about. Power.org has done an excellent job of defining a powerful core, one that is flexible and capable of being hooked-up to an almost infinite number of peripherals. And then it stops. Standard peripherals, such as an interrupt handler unit, or a debug trace unit are not defined in the standard, which means each vendor is free to implement as they wish. Arm, on the other hand, tightly integrates these “standard” peripherals into the core. Arm wins in this situation because tighter integration of debug peripherals means compatibility with standard tools; tighter integration of the interrupt handler unit means quicker interrupts (but let’s not get ahead of ourselves). This approach also helps vendors integrating the IP as they do not have to worry about handling these elements (which are more than likely far away from their target application, or from where they want to add value).

The direct effect of one approach vs. the other is quickly visible when it comes to interrupts: Arm’s Cortex-M4 guarantees a latency of 3-cycles from the time the Interrupt is flagged to the time the core is actually doing something with it. All context registers are stored automatically. The e200z0, on the other hand, will require an external controller to flag it to the core as an external interrupt. Next, some code will need to be written to ensure that the context registers are correctly stored. Finally, it is also code that will allow to jump to the pending interrupt and attend. Latency is therefore not guaranteed, and will vary from implementation to implementation.

But that is not to say that the e200z0 is inferior. Let’s take a look at Table 1:

	Cortex-M4	e200z0
Execution	IN-order	IN-order
Memory Management/Protection Unit	Y	N
Instruction Cache	N	N
Signal processing extension	Y	N
Pipeline	3-stage	4-stage
Branch unit processor	Not explicit	Y
Multiply	1	1
Integer divide cycles	2 – 12 cycles	5 – 34 cycles
Endianness	Little	Big
Architecture	Harvard	Harvard
Interrupt controller	Internal	External
Jump-to-Isr latency	3 cycles	Code dependant; several cycles
Relocatable ISR table	Yes	Yes
Debug Interfaces	JTAG, J-Link	JTAG
Number of core registers	13 + SP, LR, PC (16 total)	32 + SP, CR, LR, CTR
Instruction set supported	Thumb 16-bit instructions	VLE 16-bit instructions

Table 1.

In fact, when you look at  the generalities, the e200z0 and the Cortex-M4 are very similar: Harvard architecture, 32-bit RISC machines with no out-of-order execution and 1-cycle execution times for most instructions. Yes, the Cortex-M4 is about twice as fast ath the e200z0 when it comes to division, but the fact that the latter has double the amount of core registers means that it can economize load/store cycles.

Which brings us to the instruction set architecture.

ISA

In a similar effort, both Arm and Power.org have created extensions to their original ISA with the goal of reformatting instructions into 16-bit words to help with code density. Both communities have later released devices that are only compatible with these extensions, removing all support for the original ISA. This is the case for both the e200z0 and the Cortex-M4 with Variable Length Encoding, and Thumb ISAs, respectively.

Comparing and contrasting both ISAs probably deserves a blog entry by itself, but the gist of it is that both instruction sets have similar encodings. Perhaps worthy of a special mention is Thumb’s immediate rotate addressing mode, which allows to shift a core-register while performing another operation during the same execution cycle of the original operation.

Truth be told, both ISAs are so complex that it will be up to the compiler to fully exploit their advantages. Take, for example, the Cortex-M4 DSP extension which adds a DSP-like unit capable of 1-cycle Multiply-and-accumulate operations, among others. When writing code, a simple line such as

y = (m * x + b);

will compile using a standard sequence of loads, multiplies, stores, and adds. In order to use the DSP-extension, an abstraction layer needs to be downloaded, and function-like calls need be made (which are replaced by macros and take advantage of said extension).

Which means that code is no longer portable to, say, a PowerPC architecture.

Toolchain support

This category is tough. Both organizations have done an excellent job of standardizing their architectures, and a plethora of compilers and standard tools is available for both. Since both are also JTAG-compliant, this means that almost anything can be used to develop for them:

• gcc
• CodeWarrior
• Green Hills
• IAR Workbench (Arm only)

I’d say there’s a tie here, although there may be specialized tools on each case,debugging activities are not necessarily harder on one platform than on the other.

Conclusion

If both architectures were to hit the market for the first time today,with the same IP-based distribution model, it’s really hard to predict who would win. The Cortex-M4 is tightly integrated with an interrupt controller and debugging support, while the e200z0 allows a greater amount of customization to vendors. The Cortex-M4 allows bit-shifting as part of a register load or store, but the e200z0 doesn’t need to perform loads and stores as often because it has more core registers. The Cortex-M4 is slightly faster with fixed-point math division. Toolchain support is excellent for both architectures. Without bringing down these characteristics to specific products, it’s hard to have a winner!

[Unix / Linux Shell Tutorial - Lession 3] Directory Management

In this chapter, we will discuss in detail about directory management in Unix.

A directory is a file the solo job of which is to store the file names and the related information. All the files, whether ordinary, special, or directory, are contained in directories.

Unix uses a hierarchical structure for organizing files and directories. This structure is often referred to as a directory tree. The tree has a single root node, the slash character (/), and all other directories are contained below it.

Home Directory

The directory in which you find yourself when you first login is called your home directory.

You will be doing much of your work in your home directory and subdirectories that you'll be creating to organize your files.

You can go in your home directory anytime using the following command −

$cd ~
$

Here ~ indicates the home directory. Suppose you have to go in any other user's home directory, use the following command −

$cd ~username
$

To go in your last directory, you can use the following command −

$cd -
$

Absolute/Relative Pathnames

Directories are arranged in a hierarchy with root (/) at the top. The position of any file within the hierarchy is described by its pathname.

Elements of a pathname are separated by a /. A pathname is absolute, if it is described in relation to root, thus absolute pathnames always begin with a /.

Following are some examples of absolute filenames.

/etc/passwd
/users/sjones/chem/notes
/dev/rdsk/Os3

A pathname can also be relative to your current working directory. Relative pathnames never begin with /. Relative to user amrood's home directory, some pathnames might look like this −

chem/notes
personal/res

To determine where you are within the filesystem hierarchy at any time, enter the command pwd to print the current working directory −

$pwd
/user0/home/amrood

$

Listing Directories

To list the files in a directory, you can use the following syntax −

$ls dirname

Following is the example to list all the files contained in /usr/local directory −

$ls /usr/local

X11       bin          gimp       jikes       sbin
ace       doc          include    lib         share
atalk     etc          info       man         ami

Creating Directories

We will now understand how to create directories. Directories are created by the following command −

$mkdir dirname

Here, directory is the absolute or relative pathname of the directory you want to create. For example, the command −

$mkdir mydir
$

Creates the directory mydir in the current directory. Here is another example −

$mkdir /tmp/test-dir
$

This command creates the directory test-dir in the /tmp directory. The mkdir command produces no output if it successfully creates the requested directory.

If you give more than one directory on the command line, mkdir creates each of the directories. For example, −

$mkdir docs pub
$

Creates the directories docs and pub under the current directory.

Creating Parent Directories

We will now understand how to create parent directories. Sometimes when you want to create a directory, its parent directory or directories might not exist. In this case, mkdir issues an error message as follows −

$mkdir /tmp/amrood/test
mkdir: Failed to make directory "/tmp/amrood/test"; 
No such file or directory
$

In such cases, you can specify the -p option to the mkdir command. It creates all the necessary directories for you. For example −

$mkdir -p /tmp/amrood/test
$

The above command creates all the required parent directories.

Removing Directories

Directories can be deleted using the rmdir command as follows −

$rmdir dirname
$

Note − To remove a directory, make sure it is empty which means there should not be any file or sub-directory inside this directory.

You can remove multiple directories at a time as follows −

$rmdir dirname1 dirname2 dirname3
$

The above command removes the directories dirname1, dirname2, and dirname3, if they are empty. The rmdir command produces no output if it is successful.

Changing Directories

You can use the cd command to do more than just change to a home directory. You can use it to change to any directory by specifying a valid absolute or relative path. The syntax is as given below −

$cd dirname
$

Here, dirname is the name of the directory that you want to change to. For example, the command −

$cd /usr/local/bin
$

Changes to the directory /usr/local/bin. From this directory, you can cd to the directory /usr/home/amrood using the following relative path −

$cd ../../home/amrood
$

Renaming Directories

The mv (move) command can also be used to rename a directory. The syntax is as follows −

$mv olddir newdir
$

You can rename a directory mydir to yourdir as follows −

$mv mydir yourdir
$

The directories . (dot) and .. (dot dot)

The filename . (dot) represents the current working directory; and the filename .. (dot dot) represents the directory one level above the current working directory, often referred to as the parent directory.

If we enter the command to show a listing of the current working directories/files and use the -a option to list all the files and the -l option to provide the long listing, we will receive the following result.

$ls -la
drwxrwxr-x    4    teacher   class   2048  Jul 16 17.56 .
drwxr-xr-x    60   root              1536  Jul 13 14:18 ..
----------    1    teacher   class   4210  May 1 08:27 .profile
-rwxr-xr-x    1    teacher   class   1948  May 12 13:42 memo
$

[Unix / Linux Shell Tutorial - Lession2] File Management

In this chapter, we will discuss in detail about file management in Unix. All data in Unix is organized into files. All files are organized into directories. These directories are organized into a tree-like structure called the filesystem.

When you work with Unix, one way or another, you spend most of your time working with files. This tutorial will help you understand how to create and remove files, copy and rename them, create links to them, etc.

In Unix, there are three basic types of files −

• Ordinary Files − An ordinary file is a file on the system that contains data, text, or program instructions. In this tutorial, you look at working with ordinary files.
• Directories − Directories store both special and ordinary files. For users familiar with Windows or Mac OS, Unix directories are equivalent to folders.
• Special Files − Some special files provide access to hardware such as hard drives, CD-ROM drives, modems, and Ethernet adapters. Other special files are similar to aliases or shortcuts and enable you to access a single file using different names.

Listing Files

To list the files and directories stored in the current directory, use the following command −

$ls

Here is the sample output of the above command −

$ls

bin        hosts  lib     res.03
ch07       hw1    pub     test_results
ch07.bak   hw2    res.01  users
docs       hw3    res.02  work

The command ls supports the -l option which would help you to get more information about the listed files −

$ls -l
total 1962188

drwxrwxr-x  2 amrood amrood      4096 Dec 25 09:59 uml
-rw-rw-r--  1 amrood amrood      5341 Dec 25 08:38 uml.jpg
drwxr-xr-x  2 amrood amrood      4096 Feb 15  2006 univ
drwxr-xr-x  2 root   root        4096 Dec  9  2007 urlspedia
-rw-r--r--  1 root   root      276480 Dec  9  2007 urlspedia.tar
drwxr-xr-x  8 root   root        4096 Nov 25  2007 usr
drwxr-xr-x  2    200    300      4096 Nov 25  2007 webthumb-1.01
-rwxr-xr-x  1 root   root        3192 Nov 25  2007 webthumb.php
-rw-rw-r--  1 amrood amrood     20480 Nov 25  2007 webthumb.tar
-rw-rw-r--  1 amrood amrood      5654 Aug  9  2007 yourfile.mid
-rw-rw-r--  1 amrood amrood    166255 Aug  9  2007 yourfile.swf
drwxr-xr-x 11 amrood amrood      4096 May 29  2007 zlib-1.2.3
$

Here is the information about all the listed columns −

• First Column − Represents the file type and the permission given on the file. Below is the description of all type of files.
• Second Column − Represents the number of memory blocks taken by the file or directory.
• Third Column − Represents the owner of the file. This is the Unix user who created this file.
• Fourth Column − Represents the group of the owner. Every Unix user will have an associated group.
• Fifth Column − Represents the file size in bytes.
• Sixth Column − Represents the date and the time when this file was created or modified for the last time.
• Seventh Column − Represents the file or the directory name.

In the ls -l listing example, every file line begins with a d, -, or l. These characters indicate the type of the file that's listed.

Sr.No.	Prefix & Description
1	- Regular file, such as an ASCII text file, binary executable, or hard link.
2	b Block special file. Block input/output device file such as a physical hard drive.
3	c Character special file. Raw input/output device file such as a physical hard drive.
4	d Directory file that contains a listing of other files and directories.
5	l Symbolic link file. Links on any regular file.
6	p Named pipe. A mechanism for interprocess communications.
7	s Socket used for interprocess communication.

Metacharacters

Metacharacters have a special meaning in Unix. For example, * and ? are metacharacters. We use * to match 0 or more characters, a question mark (?) matches with a single character.

For Example −

$ls ch*.doc

Displays all the files, the names of which start with ch and end with .doc −

ch01-1.doc   ch010.doc  ch02.doc    ch03-2.doc 
ch04-1.doc   ch040.doc  ch05.doc    ch06-2.doc
ch01-2.doc ch02-1.doc c

Here, * works as meta character which matches with any character. If you want to display all the files ending with just .doc, then you can use the following command −

$ls *.doc

Hidden Files

An invisible file is one, the first character of which is the dot or the period character (.). Unix programs (including the shell) use most of these files to store configuration information.

Some common examples of the hidden files include the files −

• .profile − The Bourne shell ( sh) initialization script
• .kshrc − The Korn shell ( ksh) initialization script
• .cshrc − The C shell ( csh) initialization script
• .rhosts − The remote shell configuration file

To list the invisible files, specify the -a option to ls −

$ ls -a

.         .profile       docs     lib     test_results
..        .rhosts        hosts    pub     users
.emacs    bin            hw1      res.01  work
.exrc     ch07           hw2      res.02
.kshrc    ch07.bak       hw3      res.03
$

• Single dot (.) − This represents the current directory.
• Double dot (..) − This represents the parent directory.

Creating Files

You can use the vi editor to create ordinary files on any Unix system. You simply need to give the following command −

$ vi filename

The above command will open a file with the given filename. Now, press the key i to come into the edit mode. Once you are in the edit mode, you can start writing your content in the file as in the following program −

This is unix file....I created it for the first time.....
I'm going to save this content in this file.

Once you are done with the program, follow these steps −

• Press the key esc to come out of the edit mode.
• Press two keys Shift + ZZ together to come out of the file completely.

You will now have a file created with filename in the current directory.

$ vi filename
$

Editing Files

You can edit an existing file using the vi editor. We will discuss in short how to open an existing file −

$ vi filename

Once the file is opened, you can come in the edit mode by pressing the key iand then you can proceed by editing the file. If you want to move here and there inside a file, then first you need to come out of the edit mode by pressing the key Esc. After this, you can use the following keys to move inside a file −

• l key to move to the right side.
• h key to move to the left side.
• k key to move upside in the file.
• j key to move downside in the file.

So using the above keys, you can position your cursor wherever you want to edit. Once you are positioned, then you can use the i key to come in the edit mode. Once you are done with the editing in your file, press Esc and finally two keys Shift + ZZ together to come out of the file completely.

Display Content of a File

You can use the cat command to see the content of a file. Following is a simple example to see the content of the above created file −

$ cat filename
This is unix file....I created it for the first time.....
I'm going to save this content in this file.
$

You can display the line numbers by using the -b option along with the catcommand as follows −

$ cat -b filename
1   This is unix file....I created it for the first time.....
2   I'm going to save this content in this file.
$

Counting Words in a File

You can use the wc command to get a count of the total number of lines, words, and characters contained in a file. Following is a simple example to see the information about the file created above −

$ wc filename
2  19 103 filename
$

Here is the detail of all the four columns −

• First Column − Represents the total number of lines in the file.
• Second Column − Represents the total number of words in the file.
• Third Column − Represents the total number of bytes in the file. This is the actual size of the file.
• Fourth Column − Represents the file name.

You can give multiple files and get information about those files at a time. Following is simple syntax −

$ wc filename1 filename2 filename3

Copying Files

To make a copy of a file use the cp command. The basic syntax of the command is −

$ cp source_file destination_file

Following is the example to create a copy of the existing file filename.

$ cp filename copyfile
$

You will now find one more file copyfile in your current directory. This file will exactly be the same as the original file filename.

Renaming Files

To change the name of a file, use the mv command. Following is the basic syntax −

$ mv old_file new_file

The following program will rename the existing file filename to newfile.

$ mv filename newfile
$

The mv command will move the existing file completely into the new file. In this case, you will find only newfile in your current directory.

Deleting Files

To delete an existing file, use the rm command. Following is the basic syntax −

$ rm filename

Caution − A file may contain useful information. It is always recommended to be careful while using this Delete command. It is better to use the -i option along with rm command.

Following is the example which shows how to completely remove the existing file filename.

$ rm filename
$

You can remove multiple files at a time with the command given below −

$ rm filename1 filename2 filename3
$

Standard Unix Streams

Under normal circumstances, every Unix program has three streams (files) opened for it when it starts up −

• stdin − This is referred to as the standard input and the associated file descriptor is 0. This is also represented as STDIN. The Unix program will read the default input from STDIN.
• stdout − This is referred to as the standard output and the associated file descriptor is 1. This is also represented as STDOUT. The Unix program will write the default output at STDOUT
• stderr − This is referred to as the standard error and the associated file descriptor is 2. This is also represented as STDERR. The Unix program will write all the error messages at STDERR.