Removed some NTNU info

Reviewed-on: #4

404.html

@@ -12,4 +12,4 @@ description: Siden ble ikke funnet :(
 function goBack() {
 	history.go(-1); event.preventDefault();
 }
-</script>
+</script>

Gemfile

@@ -7,7 +7,7 @@ source "https://rubygems.org"
 #
 # This will help ensure the proper Jekyll version is running.
 # Happy Jekylling!
-gem "jekyll", "~> 4.1.1"
+gem "jekyll", "~> 4.3.0"
 # This is the default theme for new Jekyll sites. You may change this to anything you like.
 
 # If you want to use GitHub Pages, remove the "gem "jekyll"" above and
@@ -18,3 +18,5 @@ gem "jekyll", "~> 4.1.1"
 #  gem "jekyll-feed", "~> 0.12"
 #end
 
+
+gem "webrick", "~> 1.8"

LICENSE

@@ -0,0 +1,674 @@
+                    GNU GENERAL PUBLIC LICENSE
+                       Version 3, 29 June 2007
+
+ Copyright (C) 2007 Free Software Foundation, Inc. <https://fsf.org/>
+ Everyone is permitted to copy and distribute verbatim copies
+ of this license document, but changing it is not allowed.
+
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+later version.
+
+  15. Disclaimer of Warranty.
+
+  THERE IS NO WARRANTY FOR THE PROGRAM, TO THE EXTENT PERMITTED BY
+APPLICABLE LAW.  EXCEPT WHEN OTHERWISE STATED IN WRITING THE COPYRIGHT
+HOLDERS AND/OR OTHER PARTIES PROVIDE THE PROGRAM "AS IS" WITHOUT WARRANTY
+OF ANY KIND, EITHER EXPRESSED OR IMPLIED, INCLUDING, BUT NOT LIMITED TO,
+THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
+PURPOSE.  THE ENTIRE RISK AS TO THE QUALITY AND PERFORMANCE OF THE PROGRAM
+IS WITH YOU.  SHOULD THE PROGRAM PROVE DEFECTIVE, YOU ASSUME THE COST OF
+ALL NECESSARY SERVICING, REPAIR OR CORRECTION.
+
+  16. Limitation of Liability.
+
+  IN NO EVENT UNLESS REQUIRED BY APPLICABLE LAW OR AGREED TO IN WRITING
+WILL ANY COPYRIGHT HOLDER, OR ANY OTHER PARTY WHO MODIFIES AND/OR CONVEYS
+THE PROGRAM AS PERMITTED ABOVE, BE LIABLE TO YOU FOR DAMAGES, INCLUDING ANY
+GENERAL, SPECIAL, INCIDENTAL OR CONSEQUENTIAL DAMAGES ARISING OUT OF THE
+USE OR INABILITY TO USE THE PROGRAM (INCLUDING BUT NOT LIMITED TO LOSS OF
+DATA OR DATA BEING RENDERED INACCURATE OR LOSSES SUSTAINED BY YOU OR THIRD
+PARTIES OR A FAILURE OF THE PROGRAM TO OPERATE WITH ANY OTHER PROGRAMS),
+EVEN IF SUCH HOLDER OR OTHER PARTY HAS BEEN ADVISED OF THE POSSIBILITY OF
+SUCH DAMAGES.
+
+  17. Interpretation of Sections 15 and 16.
+
+  If the disclaimer of warranty and limitation of liability provided
+above cannot be given local legal effect according to their terms,
+reviewing courts shall apply local law that most closely approximates
+an absolute waiver of all civil liability in connection with the
+Program, unless a warranty or assumption of liability accompanies a
+copy of the Program in return for a fee.
+
+                     END OF TERMS AND CONDITIONS
+
+            How to Apply These Terms to Your New Programs
+
+  If you develop a new program, and you want it to be of the greatest
+possible use to the public, the best way to achieve this is to make it
+free software which everyone can redistribute and change under these terms.
+
+  To do so, attach the following notices to the program.  It is safest
+to attach them to the start of each source file to most effectively
+state the exclusion of warranty; and each file should have at least
+the "copyright" line and a pointer to where the full notice is found.
+
+    <one line to give the program's name and a brief idea of what it does.>
+    Copyright (C) <year>  <name of author>
+
+    This program is free software: you can redistribute it and/or modify
+    it under the terms of the GNU General Public License as published by
+    the Free Software Foundation, either version 3 of the License, or
+    (at your option) any later version.
+
+    This program 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 the
+    GNU General Public License for more details.
+
+    You should have received a copy of the GNU General Public License
+    along with this program.  If not, see <https://www.gnu.org/licenses/>.
+
+Also add information on how to contact you by electronic and paper mail.
+
+  If the program does terminal interaction, make it output a short
+notice like this when it starts in an interactive mode:
+
+    <program>  Copyright (C) <year>  <name of author>
+    This program comes with ABSOLUTELY NO WARRANTY; for details type `show w'.
+    This is free software, and you are welcome to redistribute it
+    under certain conditions; type `show c' for details.
+
+The hypothetical commands `show w' and `show c' should show the appropriate
+parts of the General Public License.  Of course, your program's commands
+might be different; for a GUI interface, you would use an "about box".
+
+  You should also get your employer (if you work as a programmer) or school,
+if any, to sign a "copyright disclaimer" for the program, if necessary.
+For more information on this, and how to apply and follow the GNU GPL, see
+<https://www.gnu.org/licenses/>.
+
+  The GNU General Public License does not permit incorporating your program
+into proprietary programs.  If your program is a subroutine library, you
+may consider it more useful to permit linking proprietary applications with
+the library.  If this is what you want to do, use the GNU Lesser General
+Public License instead of this License.  But first, please read
+<https://www.gnu.org/licenses/why-not-lgpl.html>.

_config.yml

@@ -36,8 +36,6 @@ author:
 collections:
   posts:
     excerpt_separator: <!--more-->
-    
-  
 
 
 markdown:         kramdown

_data/home.yml

@@ -1,7 +1,7 @@
 - 
   title: NTNU
   href: /ntnu/
-  description: Alt som er relatert til NTNU, både fag og filer. Her kan du finne tidligere eksamensoppgaver, LF, mine løsninger og oppsummeringer.
+  description: Alt som er relatert til NTNU, både fag og noen filer. Her kan du finne mine løsninger og oppsummeringer.
   icon: fa-graduation-cap
 
 - 

_data/ntnu-courses.yml

@@ -14,11 +14,11 @@
     -
       course: ttk4145
       desc: Sanntidsprogrammering, våren 2021.
-      updated: 2021-05-04
+      updated: 2021-05-18
-    -
+    # -
-      course: tiø4252
+    #   course: tiø4252
-      desc: Teknologiledelse, våren 2021.
+    #   desc: Teknologiledelse, våren 2021.
-      updated: 2021-05-04
+    #   updated: 2021-05-13
 
 # Høsten 2020
 -
@@ -79,10 +79,10 @@
       course: ttt4260
       desc: Elektronisk systemdesign og -analyse I, våren 2019.
       updated: 2019-05-05
-    - 
+    # - 
-      course: tma4105
+    #   course: tma4105
-      desc: Matematikk 2, våren 2019.
+    #   desc: Matematikk 2, våren 2019.
-      updated: 2019-05-21
+    #   updated: 2019-05-21
     - 
       course: tdt4102
       desc: Prosedyre og objektorientert programmering, våren 2019.

about.md

@@ -4,7 +4,7 @@ title: Om
 permalink: /om/
 ---
 
-Mitt navn er Øyvind Skaaden. Jeg er 22 år gammel og studerer Elektronisk systemdesign og innovasjon på NTNU.
+Mitt navn er Øyvind Skaaden. Jeg er 24 år gammel og studerer Elektronisk systemdesign og innovasjon på NTNU.
 
 Jeg er stor fan av open-source og prøver så godt jeg kan å fremme dette. 
 

index.html

@@ -1,6 +1,6 @@
 ---
 layout: layouts/home
-description: Personlig nettside for Øyvind Skaaden. Inneholder det meste av personlige prosjekter og fag fra NTNU.
+description: Personlig nettside for Øyvind Skaaden. Inneholder det meste av personlige prosjekter og noen ting fra NTNU.
 ---
 
 <div class="homepage-main">
@@ -18,4 +18,3 @@ description: Personlig nettside for Øyvind Skaaden. Inneholder det meste av per
     {% endfor %}
   </div>
 </div>
-

ntnu/21v/tfe4130/tfe4130.md

@@ -4,10 +4,6 @@ title: "TFE4130"
 description: "Bølgeforplantning"
 ---
 
-## Filer og annet
-
-Alle øvinger og andre viktige filer ligger på [git](https://git.glados.no/oyvindskaaden/TFE4130).
-
 ## Forelesninger
 
 [2021-01-12](./lectures/2021-01-12/) - Intro

ntnu/21v/tiø4252/tiø4252.md

@@ -0,0 +1,68 @@
+---
+title: TIØ4252
+description: Teknologiledelse, våren 2021
+date: 2021-05-13
+---
+
+
+## Formelark
+
+Formelark i TIØ4252 kan finnes [her][formel].
+
+Kildekoden ligger på [git][git_formel].
+
+[formel]:https://git.glados.no/oyvindskaaden/TIO4252/raw/branch/main/formelark/formelark.pdf
+[git_formel]:https://git.glados.no/oyvindskaaden/TIO4252/src/branch/main/formelark/
+
+## Eksamen
+
+Alle filer er tilgjengelig på [git][git].
+
+[git]: https://git.glados.no/oyvindskaaden/TIO4252
+
+Kombinert løsningsforslag for alle eksamener finnes [her][LF_alle].
+
+[LF_alle]:https://git.glados.no/oyvindskaaden/TIO4252/raw/branch/main/eksamen/LF.pdf
+
+| År   | Eksamen | Oppgave       | LF       |
+| :--- | :------ | :------------ | :------- |
+| 2020 | Høst    | [Oppgave][1]  | [LF][2]  |
+| 2020 | Sommer  | [Oppgave][3]  | [LF][4]  |
+| 2020 | Vår     | [Oppgave][5]  | [LF][6]  |
+| 2019 | Høst    | [Oppgave][7]  | [LF][8]  |
+| 2019 | Sommer  | [Oppgave][9]  | [LF][10] |
+| 2018 | Høst    | [Oppgave][11] | [LF][12] |
+| 2018 | Sommer  | [Oppgave][13] | [LF][14] |
+| 2018 | Vår     | [Oppgave][15] | [LF][16] |
+| 2017 | Høst    | [Oppgave][17] | [LF][18] |
+| 2017 | Vår     | [Oppgave][19] | [LF][20] |
+| 2014 | Sommer  | [Oppgave][21] | [LF][22] |
+| 2013 | Sommer  | [Oppgave][23] | [LF][24] |
+{: .table-responsive-lg .table }
+
+[1]:https://git.glados.no/oyvindskaaden/TIO4252/raw/branch/main/eksamen/20H/Eksamen_20H.pdf
+[2]:https://git.glados.no/oyvindskaaden/TIO4252/raw/branch/main/eksamen/20H/Losning_20H.pdf
+[3]:https://git.glados.no/oyvindskaaden/TIO4252/raw/branch/main/eksamen/20S/Eksamen_20S.pdf
+[4]:https://git.glados.no/oyvindskaaden/TIO4252/raw/branch/main/eksamen/20S/Losning_20S.pdf
+[5]:https://git.glados.no/oyvindskaaden/TIO4252/raw/branch/main/eksamen/20V/Eksamen_20V.pdf
+[6]:https://git.glados.no/oyvindskaaden/TIO4252/raw/branch/main/eksamen/20V/Losning_20V.pdf
+[7]:https://git.glados.no/oyvindskaaden/TIO4252/raw/branch/main/eksamen/19H/Eksamen_19H.pdf
+[8]:https://git.glados.no/oyvindskaaden/TIO4252/raw/branch/main/eksamen/19H/Losning_19H.pdf
+[9]:https://git.glados.no/oyvindskaaden/TIO4252/raw/branch/main/eksamen/19S/Eksamen_19S.pdf
+[10]:https://git.glados.no/oyvindskaaden/TIO4252/raw/branch/main/eksamen/19S/Losning_19S.pdf
+[11]:https://git.glados.no/oyvindskaaden/TIO4252/raw/branch/main/eksamen/18H/Eksamen_18H.pdf
+[12]:https://git.glados.no/oyvindskaaden/TIO4252/raw/branch/main/eksamen/18H/Losning_18H.pdf
+[13]:https://git.glados.no/oyvindskaaden/TIO4252/raw/branch/main/eksamen/18S/Eksamen_18S.pdf
+[14]:https://git.glados.no/oyvindskaaden/TIO4252/raw/branch/main/eksamen/18S/Losning_18S.pdf
+[15]:https://git.glados.no/oyvindskaaden/TIO4252/raw/branch/main/eksamen/18V/Eksamen_18V.pdf
+[16]:https://git.glados.no/oyvindskaaden/TIO4252/raw/branch/main/eksamen/18V/Losning_18V.pdf
+[17]:https://git.glados.no/oyvindskaaden/TIO4252/raw/branch/main/eksamen/17H/Eksamen_17H.pdf
+[18]:https://git.glados.no/oyvindskaaden/TIO4252/raw/branch/main/eksamen/17H/Losning_17H.pdf
+[19]:https://git.glados.no/oyvindskaaden/TIO4252/raw/branch/main/eksamen/17V/Eksamen_17V.pdf
+[20]:https://git.glados.no/oyvindskaaden/TIO4252/raw/branch/main/eksamen/17V/Losning_17V.pdf
+[21]:https://git.glados.no/oyvindskaaden/TIO4252/raw/branch/main/eksamen/14S/Eksamen_14S.pdf
+[22]:https://git.glados.no/oyvindskaaden/TIO4252/raw/branch/main/eksamen/14S/Losning_14S.pdf
+[23]:https://git.glados.no/oyvindskaaden/TIO4252/raw/branch/main/eksamen/13S/Eksamen_13S.pdf
+[24]:https://git.glados.no/oyvindskaaden/TIO4252/raw/branch/main/eksamen/13S/Losning_13S.pdf
+
+

ntnu/21v/ttk4145/summary/summary.md

@@ -26,7 +26,7 @@ Hard to capture faults.
 
 ### Traditional error handeling
 
-{% highlight c %}
+{% highlight java %}
 FILE *
 openConfigFile(){
     FILE * f = fopen("/path/to/config.conf");
@@ -63,9 +63,9 @@ This is some of the error handling real time programming have.
 * Handling of unexpected errors
 * More threads hanles errors
 * Can not test the conventional way
-  * Can only show extistence of errors
+    * Can only show extistence of errors
-  * Can not find errors in specification
+    * Can not find errors in specification
-  * Can not find race conditions
+    * Can not find race conditions
 
 The fault path is shown under.
 
@@ -103,8 +103,8 @@ To test how the systems responds for a unknown error is to insert a failed accep
 **Dynammic redunancy**
 
 * Relies on detecting the error and recovering
-  * Resend if timeout and not receiving "ack"
+    * Resend if timeout and not receiving "ack"
-  * Go with default if no messages have been received
+    * Go with default if no messages have been received
 * The acceptancetest must be good.
 
 
@@ -128,29 +128,29 @@ Find the failure modes: What could go wrong?
 **Step 3: Handling with redundancy**
 
 * Have multiple copies of the the information
-  * Use only the newest
+    * Use only the newest
 
 #### Example with communication function
 
 **Step 1: Failure modes**
 
 * Message
-  * Lost
+    * Lost
-  * Delayed
+    * Delayed
-  * Corrupted
+    * Corrupted
-  * Duplicated
+    * Duplicated
-  * Wrong recipient
+    * Wrong recipient
 
 **Step 2: Detection, Merging of errormodes and error injection**
 
 * Adding information to message
-  * Checksum
+    * Checksum
-  * Session ID
+    * Session ID
-  * Sequence number
+    * Sequence number
 * Adding "ack" on well recieved messages
 * All errors will be treaded as "Lost message"
 * Injection
-  * Occasionally throw away some messages
+    * Occasionally throw away some messages
 
 **Step 3: Handling with redundancy**
 
@@ -179,7 +179,7 @@ There are three solutions:
     * Store a checkpoint
     * Do the "side effects"
 2. Process pairs
-    * Crash and let an another process take over
+        * Crash and let an another process take over
 3. Presistent processes
 
 
@@ -198,3 +198,343 @@ A transaction is a design framework for Damage Confinement and Error Recovery.
 * **C**oncistency: Leaves the system in a consistent state when finished
 * **I**solation: Errors does not spread
 * **D**urability: Results are not lost
+
+### Atomic Actions
+
+**Resumption vs. Termination mode**
+* If we continue where we were (e.g. after the interrupt) --> *Resumption*
+* If we continue somewhere else (i.e. terminating what we where doing) --> Termination
+
+**Async Notification (AN) = Low level thread interaction**
+* Async event handling. ("Signals") (resumption)
+    * Modeled after a HW interrupt
+    * Can be sent to the correct thread
+    * Can be handled, ignored, blocked --> The domain can be controlled.
+    * Often lead to polling
+        * Could rather skip the signal and poll a status variable or a message queue
+        * Useless
+* ATC --> Async transfer of Control (termination)
+    * Canceling threads
+    * setjmpt/longjmp could convert signals to ATC (not really, but still)
+    * ADA: a strictured mechanism for ATV is integraded with the selected statement
+    * RT Java: A structured mechanism for ATC is integraded with the exception-handling mechanism
+
+#### Cancelling threads
+
+**Yes, killing threads is ATC!**
+
+* Can make termination model by letting domain be a thread
+    * "Create a `doWork` thread, and kill it if the action fails"
+* Ca still control domain by disabling "cancelstate"
+
+**But, but, but: It leaves ut in undifined state!?**
+* Not if we have...
+    * Full control over changed state (like logs or recovery points) or some other way of recovering well.
+    * A lock manager that can unlock on behalf of killed thread
+    * Some control of where we were killed (like nok in the middle of a lock manager or log call)
+* An this is what we have!
+
+
+## Shared variable synchronization
+
+### Non-Preemptive scheduling
+
+Controlling a pump filling a tank.
+
+**Spec:**
+* Every second: measure the water level of the tank and generate the reference to the pump
+* 10 times a second: Set the power of the pump motor
+* Do some GUI: let the human control the process
+
+#### A trivial solution: "Cyclic Exectutive"
+
+{% highlight java %}
+oldTime = now();
+i = 0;
+while(true) {
+    i = i + 1;
+    if (i % 10 == 0) {
+        i = 0;
+        calculatePumpReference();
+    }
+    controlPump();
+    do {
+        handleUserEvent();
+    } while(now() < oldTime + 0.1);
+    oldTime = oldTime + 0.1;
+}
+{% endhighlight %}
+
+**Drawbacks**
+
+* OK tasks?
+* Timing hard to tune (what if pump sampling should be $\pi$/10?)
+* Overload (what if `calucaltePumpReference` uses more than 1/10 seconds?)
+* How to add new tasks? (Everything is coupled)
+* Waste of time in the do-loop?
+* What is priority of `handleUserEvents`?
+* How are erros, exceptions, alarms etc. handled?
+
+#### Better soulution with Non-preemptive scheduler
+
+* *3 taskts* administered by a scheduler
+* The scheduler takes care of who runs and timing
+* Scheduler often inculuded in OSes
+* Introducing priorities
+
+{% highlight java %}
+/**
+    * scheduler_registerThread(function, time, priority)
+    * Higher priority numer means higher priority in scheduler
+    */
+main() {
+        scheduler_registrerThread(controlPump, 0.1, 3);
+        scheduler_registrerThread(calculatePumpReference, 1, 2);
+        scheduler_registrerThread(handleUserEvents, 0.2, 1);
+        scheduler_mainLoop();
+}
+{% endhighlight %}
+
+**Some notes on priorities**
+* Priority is generally not important; rather, the main rule is to give higher priority to shorter-deadline tasks. 
+    * This allows tasks to reach its deadlines.
+* ... but this is not always the case - if e.g. the tasks are cooperating
+* We still handle overload badly
+* And: What connection between deadline and priority to start with?
+    * Is this a good dependency seen from a code quality perspective?
+
+### Pros and cons of nonpreemptive scheduling
+
+| **Pros**                                       | **Cons**                                                                   |
+| :--------------------------------------------- | :------------------------------------------------------------------------- |
+| Simple, intuitive, predictable                 | C macro hell                                                               |
+| No kernel                                      | Threads must cooperate <-- a form of dependency breaking module boundaries |
+| Fast switching times                           | Heavy threads must be divided                                              |
+| Some elegant sunchronization patterns possible | Can we handle blocking of library functions?                               |
+|                                                | Unrobust to errors                                                         |
+|                                                | Unrobust to (heavy) error handling                                         |
+|                                                | Hard to tune at end of project                                             |
+{: .table-responsive-lg .table }
+
+
+
+### Preemptive Kernel
+
+* Preemption, thread objects and the timer interrupt
+* Enabling synchronization: Busy waiting, tes-and-set, disabling the timer interrupt
+* Blocking and suspend & resume
+* An API for synchronization? Semaphores!
+
+
+#### Preemption
+
+* Make a handler for a timer interrupt
+* Store all registers (including IP & SP) in a "thread object"
+* Organize queue of processes (Round Robin e.g. - a collection of thread objects?)
+* Can synchronize by: `while(!ready);` (busy wating, "spin locks")
+
+**Bad solution**
+
+{% highlight java%}
+while(lock==1) {}
+lock = 1;
+    // We may run
+lock = 0;
+{% endhighlight %}
+
+**Better solution**
+
+{% highlight java%}
+void t1() {
+    flag1 = 1;  // Declare my intention
+    turn  = 2;  // But try to be polite
+    while(flag2 == 1 && turn == 2) {}
+    // We may run
+    flag1 = 0;
+}
+{% endhighlight %}
+
+##### Looking more closely at the arsenal
+
+**How can we make basic synchronization under preemption?**
+
+* Spin locks (wasting time and cpu)
+* Test&Set (swap) assembly instruction (atomic, but not obvious)
+* Disable interrupt (steals control from OS/scheduler)
+
+**But**
+* If we disable the timer interrupt we don not have preemption any more
+* And... Are these good abstractions in the application programmer domain?
+
+#### Blocked threads
+
+**Let us introduce another queue; the collection of threads not running, waiting for something**
+
+* Fixes the bad performance of spin locks. Is conceptually better.
+* `suspend` moves a thread object from "run" queue to "blocked" queue
+* `resume` moves it back.
+
+##### Two bad solutions
+
+{% highlight java%}
+t1(){
+    while(busy == 1) suspend();
+    busy = 1;   // It is free; tak it - No
+        // Run
+    busy = 0;   // Release resource
+
+    resume t2 // No
+}
+{% endhighlight %}
+
+or 
+
+{% highlight java%}
+t1(){
+    while(TestNSet(busy, 1) == 1) suspend();
+        // We own resource
+        // Run
+    busy = 0;
+
+    resume t2 // No
+}
+{% endhighlight %}
+
+##### The suspend/resume problem
+
+{% highlight java%}
+// Global variables
+bool g_initDone = False;
+
+// Threads
+t1(){                           t2(){
+    /* Do init */                   if (g_initDone == False) {
+    g_initDone = True;                  Suspend();
+    resume(t2)                      }
+    // Continue executing           // Continue exectuting
+}                               }
+{% endhighlight %}
+
+#### Priorities
+
+* Threads mey have different *priorities*. (A sortet run-queue, or more of them.)
+* Only if there are no running threads on a higher priority, a thread will run.
+* We are not aiming for some sens of fairness (!). But predictability.
+* And priorities supports schedulability proofs.
+* But we open ourselves up to *starvation*. A thread may not ever get to run, even if it is runnable.
+
+
+#### Application-level syncronization
+
+**SO, the application programmer needs some syncronozation primitives...**
+
+* `sleep()`? - Ok
+* Publish `suspend` and `resume` - No
+* Events (`wait` and `signal`) - Just named versions of suspend & resume semantics.
+  * Fixes the need to know aboud "thread objects". But no
+* ...or "Condition variables" - same
+
+
+### Semaphores
+
+**A counting semaphore**
+
+* `signal(SEM)` increases the counter (possibly resuming a thread waiting for the semaphore)
+* `wait(SEM)` decrements the counter - will block (be suspended) `if SEM == 0`
+  * The semaphores value can not be negative
+* Of course; These calls are protected from interleaving by disabling the timer interrupt
+
+**We solve beautifully:**
+* Mutual Exclusion
+* Conditional Synchronization (ref `suspend`/`resume`)
+* Basic resource allocation
+
+**Semaphore variations**
+
+* `wait` and `signal` nay take parameter value to add or subtract
+* `getValue(SEM)` returning the value of the semaphore. (Fishy)
+* BInary semaphores (`signal` will fail `if SEM == 1`)
+* Who is woken at `signal` (FIFO, Arbitrary, Highest priority)
+* The mutex
+  * binary
+  * ownership
+  * allows mulitple waits by owner
+  * regions (may be released by Javas `wait` or POSIX condition variables)
+* RTFM
+
+**Semaphore challenges**
+
+* Breaks modules (both ways)
+  * Does not scale!
+* Deadlocks
+  * Global analysis --> Does not scale
+* Can not release "temporarily
+* "Limited expressive power". Some reasonalbe problems are hard to solve
+  * Ref ["The Little Book of Semaphores"](https://greenteapress.com/semaphores/LittleBookOfSemaphores.pdf)
+
+### Why shared-variable synchronization
+
+**Why not?**
+
+* "Shared variables" is bad code quality
+  * Ref global variables, and data members in module interfaces
+* An obvious bottleneck? Scales terribly
+* "Variables" are passive objects
+  * They can not protect themselves
+* Why use synchronization when it is communication we need?
+* Technology transfers badly to distibuted systems
+* ... and this is before we start discussing how hard it is
+
+**Why?**
+
+* Part of the "real-time" design pattern
+  * "One thread per timing demand" 
+  * We do have scheduling proofs and best practises
+* Timing analysis is global anyway
+  * Scalability and deadlock analysis may not be the limiting constraint
+* HW is shared memory architecture
+  * Infrastucture is avalible
+* Communication systems requires infrastucture that we may not have
+
+#### *All* resources are shared!
+
+* Memory, certainly
+* "Hidden" memory used by libraries (.. your own modules and the kernel)
+  * If the library takes care of this itself, it is called *"reentrant"*
+* Sensors and actuators
+* "CPU" - Computing capacity 
+  * *This* is real-time programming; We solve it by *Scheduling*
+* ... any other interface
+
+
+#### Some standard problems/pit-falls
+
+* **Race condition**: A bug that surfaces by unfortunate timing or order of events
+* **Deadlock:** system in circular wait
+  * Special case of livelock
+  * Does not use CPU
+* **Livelock:** system locked in a subset of states 
+  * like deadlock, but we use CPU
+  * Busy-Waiting is a livelock
+* **Starvation:** A thread does "by accident" not get the necessary resources
+
+
+#### Features in syncronization
+
+* Critical Section - Code that must not be interupted
+* Mutual Exclusion - More piecesof code that must not interrupt each other
+* Bounded buffer - Buffer with full/empty synchronization
+* Read/Write Locks
+  * Readers can interleave eachother
+  * Writers have mutual exclusion
+* Condition Syncronization - Blocking on event or status
+  * Guards etc.
+* Resource allocation
+  * More than mutual exclution!
+  * Ref: The lock manager
+* Rendezvouz/barriere - Synchronization point
+  * Ref: AA "end boundary"
+* Communication
+* Broadcast
+* ...
+

ntnu/21v/ttk4145/ttk4145.md

@@ -8,8 +8,4 @@ description: "Sanntidsprogrammering"
 
 [Oppsummering](summary/) av faget TTK4145.
 
-## Prosjekt
-
-## Øvinger
-