For low power, is LL better than HAL?

[S.Ma]

It is quite similar to the following question:

Is writing in assembly language better than C ?

Going lower level enables more control... for who has the tech know how for it.

Saving power is relative, there maybe many ways to reduce power, only few will have a significant impact.... power saving starts with a mission profile. Then, usually follows the question: what is the lowest core frequency that meet the application needs, to minimize the active and running power, then the power saving mode (clock stop...).... is the application sleeping 50% or 98% of the time?

HAL vs LL may require higher core frequency if more code is run relatively. Similarly for RTOS/linux vs Bare metal... trade offs are.to be well selected.

[TheRaprus]

Generally speaking I agree with you, but two things:

Using LL need deepest knowledge of the micro (and this is a must for the best solution ever).

From the ST website: "The general rule to minimize the power consumption is to perform the task for the shortest possible time, at the lowest possible operating frequency and with the clock enabled to a minimal part of the silicon."

HAL need SysTick "The SysTick timer is configured to be used to generate variable increments by calling HAL_IncTick() function in SysTick ISR and retrieve the value of this variable by calling HAL_GetTick() function. The call HAL_GetTick() function is mandatory when using HAL drivers with Polling Process or when using HAL_Delay()." So, to reach the best low consumption SysTick must be enabled on wakeUp and vice-versa. ISR is shortest using LL than HAL, and they don't need SysTick .

The point can be: is a HAL ISR 20% slowest than LL, and it's called every minute, is the effort to learn all the uC so deep necessary?

I saw code where the LL are "copied" inside a ISR or a routine, like this:

GPIOA->ODR &= ~(1<<4); {

   while (!((SPI1->SR)&(1<<1))) {};

   SPI1->DR = opcode; }

>> illeggible!

In the past I used the Standard Template Library, and I prefer LL than HAL. But many lazy programmers use HAL without knowing how they work...

[S.Ma]

Well the 1 msec interrupt could use an lptim in some families so in between clock stop is possiblr.

[Tesla DeLorean]

Coding just what you need will tend to be the most efficient.

The HAL is a bit of a train wreck in many respects, and the paradigms it uses are often unhelpful ​and forced.

[LCE]

I was actually surprised that the LL stuff I had a look at seemed only like a slightly toned down HAL.

So in case of doubt, write and read the registers directly.

[TheRaprus]

Sometime yes. Ofcourse, if you search only a bit set/reset OK. On a serial R/W interrupt things are most compicated (for me in HAL mode :face_with_tears_of_joy:). Unfortunately good library (as HAL are IMHO) makes programmers lazy.