STM32L451 comparator settings with VREFINTx inputs

Hello,

If it was indicated by the reference manual especially the RM0394 / the note under the figure 118, no need to indicate the reason why this was not implemented nor to indicate it in the errata sheet.

Perhaps, it was a choice by the design to not implement the VERFINTxxx on L45xx and L46xx as COMP inputs.

This is a nasty documentation fail... I believe it's a design bug disguised as documented feature, but documented extremely poorly.

Also in DS:

If DAC_CH2 is not connected, than that should be documented too.

JW

[EDIT] I've just noticed there's no 'L461; 'L45x/'L46x would be more appropriate; sorry.

[EDIT2] There's no DAC_CH2 in 'L45x/'L46x, that's documented properly in the DAC chapter and DS; should be mentioned in the INMSEL fields description, and the Fig.118 footnote should be formulated clearer.

[EDIT3] 

Footnote to say unavailability of Vrefint and fractions, and DAC_CH2, should be added to Table 90. COMP1 input minus assignment and Table 92. COMP2 input minus assignment, too

Also, COMPx_CSR.SCALEN and COMPx_CSR.BRGEN appear to be linked to Vrefint and fractions. It would be nice if they would be depicted in Fig.118. The "bandgap" term should not be used in description of those bits, as this term is not explained/mentioned anywhere else in the RM (it is in the ADC chapter, where it may be confusing either). "Internal reference voltage", or "Vrefint" is used everywhere else.

The case was internally escalated over this internal ticket CDM0062827 for follow-up.

I looked also at Cube (not CubeMX, I don't use it and don't intend to install/run/learn).

In stm32l4xx_hal_comp.c, there's a table listing the options for comparator inputs/outputs. It lists exceptions for 'L41x/'L42x and for 'L43x/'L44x, for which I can't find references in the COMP chapter in RM0394, and, sure, doesn't list the exceptions for 'L45x/'L46x. Haven't had look at the actual code, if it performs some actual validity checks in this regard.

In stm32l4xx_ll_comp.c, there's an actual check, which does not take into account the discussed 'L45x/'L46x exception.

(Just to explain my surge of activity here: I do use the 'L431 and 'L451 actively in a group of projects, and although not COMP so far, it may happen such requirement will come one day as we've expanded the scope already several times, and I don't want to be surprised either. Btw. these are chips with a really nice set of features, truly.)

JW

> every time I set VREFINT as the reference source, the MCU immediately jumps into a hard fault

That's IMO unexpected and I would say there's some other unrelated reason.

Perhaps show, what expression exactly leads to that hardfault.

JW

@mƎALLEm ,

Thanks for this information. So, it appears, that - apart from the confusing footnote in Fig.118 - the probem was probably somewhere in  @y_liosha 's code, correct?

Can you also please have a look at this:

Thanks,

JW

Preferably to ask the question related to the comp driver in the STM32 Embedded software. 

I'll check the documentation next Monday.

@mƎALLEm , thanks.

JW