STM32F4 - CRC implementation faulty

[RajaSrinivasan]

STM32.CRC defines a new type:

private

type CRC_32 is new STM32_SVD.CRC.CRC_Peripheral;

The above leads to creating new variables instead of accessing the singleton object CRC_Periph located at a specific address.

CRC calculations fail due to this - always returning the last value written to the DR

[pat-rogers]

Hello,
You are correct, the package itself is insufficient.
The idea is that there should be an object declaration for the CRC unit in the specific device's STM32.Devices package, but a misunderstanding prevented that except for the F4 series (and maybe others, I didn't check). For example, I have just opened PR #465 to add the declaration to the Devices package for the F7x series. I assume that the STM32.Devices package you're using does not have the CRC unit declaration. You can either manually add it to the STM32.Device package for the device you're using (and open a PR for it), or just declare a local variable of the CRC_32 type and reference that. If you add it to the Devices package you need to add ther Enable_Clock procedure too. For an example of the local declaration approach/hack/workaround:

with STM32_SVD.RCC;
with STM32.CRC; use STM32.CRC; -- make a local copy of this unit's files if you don't have them via the ADL gpr file
...
package body App_Foo is

CRC_Unit : CRC_32 with Address => STM32_SVD.CRC_Base, Volatile, Import;

-- references to the CRC unit above.
...

begin -- package body executable part
STM32_SVD.RCC.RCC_Periph.AHB1ENR.CRCEN := True; -- enable the clock
-- We must enable the clock the unit is used
end App_Foo;

Alternatively, you could put the CRC_Unit declaration in a local package spec, if multiple application units will require it. But don't forget to the enable clock, in any case.

Best regards,
Pat Rogers