Arduino and assembly code

Using Arduino Programming Questions
1

Is there a tool some where that lets you paste in a simple C/C++ code snippet and have it spit out the appropriate optimised assembly code?

I did assembler years ago with the 8086 processor.

And I'd rather learn assembler with Arduino/ESP32 via reverse engineering with a tool.

     asm volatile(
          "headB:"
          "\n\t"
          "out  %[port] , %[hi]"
          "\n\t"
          "mov  %[n2]   , %[lo]"
          "\n\t"
          "out  %[port] , %[n1]"
          "\n\t"
          "rjmp .+0"
          "\n\t"
          "sbrc %[byte] , 6"
          "\n\t"
          "mov %[n2]   , %[hi]"
          "\n\t"
          "out  %[port] , %[lo]"
          "\n\t"
          "rjmp .+0"
          "\n\t"
          "out  %[port] , %[hi]"
          "\n\t"
          "mov  %[n1]   , %[lo]"
          "\n\t"
          "out  %[port] , %[n2]"
          "\n\t"
          "rjmp .+0"
          "\n\t"
          "sbrc %[byte] , 5"
          "\n\t"
          "mov %[n1]   , %[hi]"
          "\n\t"
          "out  %[port] , %[lo]"
          "\n\t"
          "rjmp .+0"
          "\n\t"
          "out  %[port] , %[hi]"
          "\n\t"
          "mov  %[n2]   , %[lo]"
          "\n\t"
          "out  %[port] , %[n1]"
          "\n\t"
          "rjmp .+0"
          "\n\t"
          "sbrc %[byte] , 4"
          "\n\t"
          "mov %[n2]   , %[hi]"
          "\n\t"
          "out  %[port] , %[lo]"
          "\n\t"
          "rjmp .+0"
          "\n\t"
          "out  %[port] , %[hi]"
          "\n\t"
          "mov  %[n1]   , %[lo]"
          "\n\t"
          "out  %[port] , %[n2]"
          "\n\t"
          "rjmp .+0"
          "\n\t"
          "sbrc %[byte] , 3"
          "\n\t"
          "mov %[n1]   , %[hi]"
          "\n\t"
          "out  %[port] , %[lo]"
          "\n\t"
          "rjmp .+0"
          "\n\t"
          "out  %[port] , %[hi]"
          "\n\t"
          "mov  %[n2]   , %[lo]"
          "\n\t"
          "out  %[port] , %[n1]"
          "\n\t"
          "rjmp .+0"
          "\n\t"
          "sbrc %[byte] , 2"
          "\n\t"
          "mov %[n2]   , %[hi]"
          "\n\t"
          "out  %[port] , %[lo]"
          "\n\t"
          "rjmp .+0"
          "\n\t"
          "out  %[port] , %[hi]"
          "\n\t"
          "mov  %[n1]   , %[lo]"
          "\n\t"
          "out  %[port] , %[n2]"
          "\n\t"
          "rjmp .+0"
          "\n\t"
          "sbrc %[byte] , 1"
          "\n\t"
          "mov %[n1]   , %[hi]"
          "\n\t"
          "out  %[port] , %[lo]"
          "\n\t"
          "rjmp .+0"
          "\n\t"
          "out  %[port] , %[hi]"
          "\n\t"
          "mov  %[n2]   , %[lo]"
          "\n\t"
          "out  %[port] , %[n1]"
          "\n\t"
          "rjmp .+0"
          "\n\t"
          "sbrc %[byte] , 0"
          "\n\t"
          "mov %[n2]   , %[hi]"
          "\n\t"
          "out  %[port] , %[lo]"
          "\n\t"
          "sbiw %[count], 1"
          "\n\t"
          "out  %[port] , %[hi]"
          "\n\t"
          "mov  %[n1]   , %[lo]"
          "\n\t"
          "out  %[port] , %[n2]"
          "\n\t"
          "ld   %[byte] , %a[ptr]+"
          "\n\t"
          "sbrc %[byte] , 7"
          "\n\t"
          "mov %[n1]   , %[hi]"
          "\n\t"
          "out  %[port] , %[lo]"
          "\n\t"
          "brne headB"
          "\n"
          : [byte] "+r"(b), [n1] "+r"(n1), [n2] "+r"(n2), [count] "+w"(i)
          : [port] "I"(_SFR_IO_ADDR(PORTB)), [ptr] "e"(ptr), [hi] "r"(hi),
            [lo] "r"(lo));
2

Not tested , but might or might not work.

https://sourceforge.net/projects/arduino-to-assembly-converter/

3

Hi @gregaryb. Here is a nice website you might find useful:

1 Like
4

looks like gcc -c -Sfilename

5

You can use Wokwi.com to simulate an Arduino running code and also view the assembler code. The F1 function exposes the option.

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image855×833 54.3 KB

This was the code running on an Arduino Uno (AVR architecture):

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image539×492 18.2 KB