STMCUBEIDE - H7 series force use of SMLAL (Signed Multiply with Accumulate (32 × 32 + 64), 64-bit result) instruction

[MikeDB]

Code is :

int16_t 	OscPhase[NumOsc];
int32_t 	OscInc[NumOsc];
int32_t 	OscVol[NumOsc];
int32_t 	Sine[65536];
 
int64_t 	OscTotal;
 
 
and then in main() :
 
		OscTotal = 0;
		for (i = 0; i < NumOsc; i++)
		{
			OscPhase[i] = OscPhase[i] + OscInc[i];
			OscTotal = OscTotal + Sine[OscPhase[i]] * OscVol[i];
		}

I was expecting the H7 to use the SMLAL instruction for the final multiply and accumulate but instead it performs a MUL.W which only gives a 32 bit result and then uses an ADD.W and ADC.W to add these 32 bits into the final 64 bit result.

Any suggestions on how to force it to use the correct code ?

[waclawek.jan]

Use inline assembler.

JW

[MikeDB]

Oh come on, this is the 21st century. Even the Arduino compiler produces better code than this managed so I'm sure it's just a compiler directive or something I am missing.

[waclawek.jan]

Then use Arduino.

JW

[MikeDB]

It doesn't support the full M7 instruction set. Only the M0/3.

[Ozone]

Does the shiny new STMCubeIDE support the M7 fully ? Including the H7 ?

Else, get a proper toolchain.

[Tesla DeLorean]

Try casting Sine with (int64_t) in the computaion.

[MikeDB]

Amazingly that works !!

ldr.w   r3, [r9, r0, lsl #2]

smlal   r4, r5, r1, r3

Definition of SMLAL is

SMLAL       R4, R5, R1, R3   ; Signed (R5,R4) = (R5,R4) + R1 × R3

Casting Sine to be 64 bits surely should force a 32*64 multiply but in fact it is indeed creating a 32*32 multiply (R1 x R3) ?

Methinks there is a bug in the compiler !

[Tesla DeLorean]

>>Methinks there is a bug in the compiler !

It is GNU, try something more industrial..