What you learn today
- Count run time per tick
- Split long loops
- yield in the right place
A pressure vessel is being watched, and at the same time the chip should form the average of the last 64 readings. The sum over 64 values needs around 300 executions. If it runs in one go, the overpressure alarm comes two or three ticks too late. For a pressure vessel that is a second too many.
Counting run time per tick
The chip executes at most 128 steps per tick. Then it pauses and carries on at the same place in the next tick – without an error. In the game code every step is a line: comment lines, blank lines and labels the chip runs over cost a step too.
| Line | costs |
|---|---|
| instruction | 1 |
| comment or blank line in the way | 1 |
| label jumped to or passed | 1 |
yield | 1, then the tick is over |
So a loop with five instructions and one label costs six steps per pass. For 64 values that is 384 steps – three ticks.
Splitting long loops
The solution: the long work is broken into portions. Every tick one piece runs, and a counter remembers where to carry on. Only after the last piece is the result output.
add end i PORTION
portion:
get tmp db i
add total total tmp
add i i 1
blt i end portion
blt i SLOTS start # not done yet: next tick
div tmp total SLOTS
sbn DISP HASH("Mittel") Setting tmpEight values per tick cost around 40 steps. After eight ticks the sum is done, and the chip still has enough room for everything else in every tick.
yield in the right place
The fast part – the overpressure watch – sits right after the yield and therefore runs first in every tick. The portion comes after it. When a portion is done, the chip jumps back to the yield instead of adding the next portion:
- Watches, switches, safety: every tick, at the front.
- Statistics, searching, sorting: in portions, at the back.
- Output of the result: only when all portions are through.
Without yield in the main loop the chip pauses in the middle of any line. The outputs of a loop can then be half done, and where the next tick begins depends on the length of the loop. A deliberate yield makes the flow predictable.
Comments inside a loop cost a step on every pass. Write them before the loop or use the game version, which removes them.
Diagram
Exercise
Task
The chip watches the vessel “Kessel” and forms the average of the last 64 pressure values:
- every tick: light “Druck” on above 200 kPa or without the sensor, then the value into the ring buffer (64 slots)
- after that sum up 8 buffer slots; after all 64 show the average on the display “Mittel” and start again
- the watch must run in every tick
Hints
Hint 1
Watch first: sgt, snan, or, sbn. Then skip the storing with bnan.
Hint 2
Portion: add end i PORTION, loop up to end, then blt i SLOTS start.
Hint 3
Only when i reaches 64 output the average and set total and i to 0.
Quiz
3 questions. You pass from 60 % – the server does the grading.
Complete the day
- Passed the simulator exercise
- Passed the quiz with at least 60 %
Without an account progress is saved in this browser only.
Report a mistake in this lesson
Please sign in to report. Sign in