diff --git a/_data/ntnu-courses.yml b/_data/ntnu-courses.yml
index 91c39f0..400af56 100644
--- a/_data/ntnu-courses.yml
+++ b/_data/ntnu-courses.yml
@@ -15,6 +15,10 @@
course: ttk4145
desc: Sanntidsprogrammering, våren 2021.
updated: 2021-05-04
+ -
+ course: tiø4252
+ desc: Teknologiledelse, våren 2021.
+ updated: 2021-05-04
# Høsten 2020
-
diff --git a/ntnu/21v/ttk4145/summary/figures/fault-path.svg b/ntnu/21v/ttk4145/summary/figures/fault-path.svg
new file mode 100644
index 0000000..dbdb06e
--- /dev/null
+++ b/ntnu/21v/ttk4145/summary/figures/fault-path.svg
@@ -0,0 +1,3 @@
+
+
+
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diff --git a/ntnu/21v/ttk4145/summary/figures/fault-tolarance.svg b/ntnu/21v/ttk4145/summary/figures/fault-tolarance.svg
new file mode 100644
index 0000000..4d88bd6
--- /dev/null
+++ b/ntnu/21v/ttk4145/summary/figures/fault-tolarance.svg
@@ -0,0 +1,3 @@
+
+
+
\ No newline at end of file
diff --git a/ntnu/21v/ttk4145/summary/summary.md b/ntnu/21v/ttk4145/summary/summary.md
new file mode 100644
index 0000000..91fa2d1
--- /dev/null
+++ b/ntnu/21v/ttk4145/summary/summary.md
@@ -0,0 +1,110 @@
+---
+title: "Oppsumering av TTK4145"
+description: "Lot of theory and discussion, some fomulas, spring 2021."
+date: 2021-05-04
+math: true
+---
+
+## Fault tolerance
+
+Hard to capture faults.
+
+
+### Bugs
+
+* 1 bug per 50 lines before testing
+* 1 bug per 500 at release
+* 1 bug per 550 after a year, the constant
+
+1. Make the program work within specs.
+2. Run/Tests of the program-
+3. Errors happen
+4. Locate errors
+ * Incomplete spec
+ * Missing handleling of som situation
+5. Fix code
+
+### Traditional error handeling
+
+{% highlight c %}
+FILE *
+openConfigFile(){
+ FILE * f = fopen("/path/to/config.conf");
+ if (f == NULL) {
+ switch(errno){
+ case ENOMEM: {
+ ...
+ break;
+ }
+ case ENOTDIR: {
+ ...
+ break;
+ }
+ // Do this for all errors
+ }
+ }
+}
+{% endhighlight %}
+
+### Causes of errors
+
+* Incomplete specification
+* Software bugs
+* HW problems
+* Communication problems
+
+### Fault tolerance in real time systems
+
+The problem with traditional errorhandleing is that errors can happen at any possible time.
+This is extremely hard to test.
+
+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 not find errors in specification
+ * Can not find race conditions
+
+The fault path is shown under.
+
+
+
+With fault tolerance the path looks something more like the figure under.
+
+
+
+### Error handling
+
+Keep it simple!
+
+The error modes is a part of the module interface.
+
+One way is to handle all errors the same way.
+Handle the as if it was the worst error.
+Crash and start again.
+
+A different approach is to check that everything is OK.
+
+To test how the systems responds for a unknown error is to insert a failed acceptance test (a not OK signal).
+
+### Redundancy
+
+* If I have $N$ copies of my data, it is possible to handle that one is destroyed.
+* Sending $N$ messages, trying $N$ times.
+
+**Static redundancy**
+
+* $N$ active copies. Sending $N$ messages if it is necessary or not.
+* Detecting errors is not important.
+* Handles cosmic rays easily.
+
+**Dynammic redunancy**
+
+* Relies on detecting the error and recovering
+ * Resend if timeout and not receiving "ack"
+ * Go with default if no messages have been received
+* The acceptancetest must be good.
+
+
\ No newline at end of file
diff --git a/ntnu/21v/ttk4145/ttk4145.md b/ntnu/21v/ttk4145/ttk4145.md
index 48cd945..602fa78 100644
--- a/ntnu/21v/ttk4145/ttk4145.md
+++ b/ntnu/21v/ttk4145/ttk4145.md
@@ -6,6 +6,8 @@ description: "Sanntidsprogrammering"
## Oppsummering
+[Oppsummering](summary/) av faget TTK4145.
+
## Prosjekt
## Øvinger