Is there a particular way I am supposed to type out commands in asm(); ?
asm (
*"SET R30, R30, 0x15"*
);
Assembly statement "SET R30, R30, 0x15"
creates a label, which may not be what was intended.
On Monday, November 6, 2017 at 3:42:17 AM UTC+5:30, Przemek Klosowski wrote:
>
>
>
> On Sun, Nov 5, 2017 at 10:07 AM, Alek Mabry <[email protected]
> <javascript:>> wrote:
>
>>
>>
>> However in the C code, I have no idea what it's actually doing in
>> assembly.
>>
>> Take a function for example, if I make a void function, will the
>> assembler have a command that jumps to that part of the code, and then
>> jumps back (adding two cycles or so), or will it just insert that code into
>> wherever the function is called?
>>
> Well, the C compiler is just essentially generating machine code, just
> lilke assembler---it's just that in assembler you specify the instructions,
> so there's a simple 1:1 correspondence. You can force the compiler to list
> the generated assembly and count instructions. You can also inject assembly
> into your function using asm() compiler extensions; typically, you would
> insert such assembly in the middle of a function. You can also call your C
> functions from such assembly but it's a little tricky because you have to
> observe the compiler ABI for register saving, stack operations and
> parameter passing.
>
>>
>> Is there any way to force the C program to do something in a specified
>> number of cycles, figure out how many cycles the C code is taking, or just
>> write assembly for time-critical parts directly into the C code itself?
>>
> You can inspect the generated code, and count instructions to get the
> cycles. You obviously can't force the compiler to use less cycles than it
> already uses in an optimized compile, but you can in principle pad with
> NOPs to artificially increase the cycle count.
>
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