Optimize Your Arduino Code with Registers

For some interesting discussion and debate about the merits of doing this, see the following Reddit threads:

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[NTG]

Didn't realize registers were a thing. You definitely inspired some new thought today. Good work!

[ezion]

AVR is one of very few processor families specifically designed to be programed in assembly. Doing so is not much harder than using a higher level language. If speed and fine control over register use is what you after, assembly might be worth looking in to.
For example: You may give a routine (function) exclusive use of some of the 32 general purpose registers instead of using variables in memory, reducing the need to push and pull from stack and heap. This can give significant performance gains. Frequently called interrupts are a good target for this technique.

[shunnoysarkar]

Hey thanks a tonne Ben! Also thank you for citing Spark Fun's video on registers!

[gordmills]

Now write it in asm. For example, I wrote code that does exactly the same functions as multiple libraries, spi negotiation, i2c communication, in asm, and it compiles to just over 1.5kb…. The original code is over 24kb… there again I’m an old fart who started when memory was premium… you had to be efficient.

[esunisen]

Reminds me the good ol' time when i had to generate a 50 Hz sinewave signal with a 68705P3 and a DAC.
I had to track every microsecond to have the right frequency.

You kids have no idea how easier it is nowadays xD

[SKNMI]

I feel it shouldn't be necessary to bang on registers manually; That sort of thing should be resolved by the compiler.

[BrainTrance]

Two questions:
1.Is the faster/efficient code written in C? is that the reason why delay() converted into _delay_ms()?
2. Isn't it faster to bit operate the PORTB rather than reassign it a new value?

[akash]

Knowledgeable information, sir how to convert delay code into millis function?

[Johann]

Why not create a translator that will translate into registers? Wandering why Arduino IDE does not do that translation…

[brucemangy]

I strongly believe that the compiler should do that for us :( i'm disappointed.

[edgarbonet]

Do not write it is hard to read and error-prone. Write `_BV(PB5)` or `(1<<PB5)`: it's just as fast (it gives the same generated assembly) and makes it very clear that you are fiddling with pin PB5.

[dw]

Very nicely done!!!! Sincere thanks!

[IamSJ]

they should make macros using the constexpr that would be clean

[samarmany]

Where is position of accumulator memory in arduino like as microcontroller AT89S51??? how to acces and save??

[pocopoco]

Chat gpt said that we can store out libraries and parts of the program(Sketch) in SD card, I didn't find any video tutorial on this, how its done?

[TericT]

Any tips on finding the documentation for such registers? I always find that to be incredibly difficult.

[imamnegeri]

Wow, its very helpful with complex project algorithm on arduino. Could you please share your documents about this? Thanks

[nonaak]

and how to do IF THEN ELSE in register code. great fid you make. thanks

[nobodyeverybody]

how to learn about the registers and keywords?

[osamarabee]

some codes dosnot work with this methos i transfered a oled and dht sensor to this methos and it was impossible to work