From 749c2a4e16e07f22fa6c42c95d0391197b8f9a64 Mon Sep 17 00:00:00 2001 From: =?UTF-8?q?=C3=98yvind?= Date: Tue, 4 May 2021 22:24:30 +0200 Subject: [PATCH] Wrap up of day 1 in exam period spring 2021 --- _data/ntnu-courses.yml | 4 + .../ttk4145/summary/figures/fault-path.svg | 3 + .../summary/figures/fault-tolarance.svg | 3 + ntnu/21v/ttk4145/summary/summary.md | 110 ++++++++++++++++++ ntnu/21v/ttk4145/ttk4145.md | 2 + 5 files changed, 122 insertions(+) create mode 100644 ntnu/21v/ttk4145/summary/figures/fault-path.svg create mode 100644 ntnu/21v/ttk4145/summary/figures/fault-tolarance.svg create mode 100644 ntnu/21v/ttk4145/summary/summary.md 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 @@ + + +
Fault
Fault
Error
Error
Failure
Failure
"The bug"
"The bug"
"The event"
What happened
"The event"...
The system failed to behave according to specification
The system fail...Viewer does not support full SVG 1.1 \ No newline at end of file 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 @@ + + +
Fault tolerance
Fault tolerance
Fault prevention
Fault prevention
Avoidance
Avoidance
Removal
Removal
"Metodologies"
"How we work with the code"
"Metodologies"...
Testing
Code inspection
Testing...
Preventing Failures
Preventing Failu...
Preventing errors becoming failures
Preventing errors becoming...Viewer does not support full SVG 1.1 \ 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. + +![Fault tolerance](figures/fault-path.svg) + +With fault tolerance the path looks something more like the figure under. + +![Fault tolerance](figures/fault-tolarance.svg) + +### 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