Thursday, May 10, 2018

Bluepill+: Diagnosing bad solder joints

If your like me... a FW engineer attempting to do soldering then this might sound familiar. I have been replacing Bluepill STM32F103C8's with STM32L443CC chips. Its a hack as I do it as I use hot air for the remove and then residual pad solder for the stick down of the replacement.

Not surprisingly, some pads don't get good adhesion. Worse, some pads don't show this lack of adhesion until much later when you need the pad to do something useful.

The STM32 series are quite good, I think all user pads can be made into GPIOs. What if we wrote a program that toggled each pad every second and then walked the pins with a meter. So that program was written.

That's great! Take a look at that code for the abstraction on the GPIOs that the Ada Device Library provides with

type GPIO_Points is array (Positive range <>) of GPIO_Point;

The magic decl in pinny is:

BP_Points : GPIO_Points :=
PB0 & PB1 & PB3 & PB4 & PB5 & PB6 & PB7 & PB8 &
PB9 & PB10 & PB11 & PB12 & PB13 & PB14 & PB15 &
PA0 & PA1 & PA2 & PA3 & PA4 & PA5 & PA6 & PA7 &
PA8 & PA9 & PA10 & PA11 & PA12 & PA15 &
PC13 & PC14 & PC15;

& concatenates items together, in this case of GPIO_Point making the init of the array BP_Points.

After that, we can just say:


The lib has code to accept the array and it will walk each element and toggle each one.

So that is every useful pin on a Bluepill highlighted above in the decl. With the abstraction of the pins to be a single element, initialization and group change becomes trivial and a small amount of user code.

A corridor conversation with a co-worker, Tyson Leistiko followed. As I described my software he mentioned I should group the GPIOs in such a way that neighboring pins toggle asymmetrically and in that way look for non 3v, 0v pins indicating some form of pin bridging. So pinny was adapted easily to add two hand picked sets that reflect the property of being neighbors to the other set.

As so:

Set1 : GPIO_Points :=
PC13 & PC15 & PA1 & PA4 & PA6 & PB0 & PB10 & PB12 &
PB14 & PA8 & PA10 & PA12 & PB3 & PB5 & PB7 & PB9;

Set2 : GPIO_Points :=
PC14 & PA0 & PA2 & PA3 & PA5 & PA7 & PB1 & PB11 &
PB13 & PB15 & PA9 & PA11 & PA15 & PB4 & PB6 & PB8;

Post those decl's we can preload the sets as so:

Clear (Set1);
Set (Set2);

Then both pinny programs go into a loop allowing you to probe all the pins for the 3v -> 0v -> 3v .. pattern.

Toggle (BP_Points);
delay until Clock + Milliseconds (1000);
end loop;

It should be said my friend Eric Schlaepfer mentioned that the EE way of doing this is to probe
the ESD diodes and look for pad to pin connectivity that way. My solution: a FW engineer caused the
problem, a FW way was used to repair the problem 😀

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