OK - after some time and retries:

I received the new ordered HAT.
I took your Linux-Image and tried again.
Changing of the i2c Adress did not work...
What worked was to update the Firmware to the 2024.hex
After FW-Update now changing the adress works as well.
Also changing dtoverlay of the ds1307 to the adress 0x48

--> Finally after 40h and your great support I think it's running - Thank you

@ryf 

Hi,

The former HAT one must be working. We have extremely low number of faulty boards. If it is not working please send me your postal address, so I ship you new one with our costs. It is practically impossible that it is not working. We have installed tens of thousands of UPS PIco HV4.0 over the world working 24/24/7/7. If you like can send you new one (but green not red, red is not available anymore). Alternatively can send you M.2 – UPS and Power Management HAT for Raspberry Pi® 5, instead. 

Please contact me with your details on support@pimodules.com

BR PiM

Still having a problem when my second-Device (SigmaDSP) is on the bus.

May any i2c professional can help me, --> see detailed analysis attached.

- UPS only works (also with the high baudrate i need for the DSP)
  --> for it doesn't look like the clock-stretching problem
- both devices release the bus properly
- UPS not responding when the DSP ist on the bus...

PS: UPS on Adr 0x48...   DSP on Adr 0x38

another pic attached, why is there a 0 on the last bit when working and a 1 when not working?

OK - One step further:

If I start the system without my DSP and connect it later, everything works.

What I do on startup, I write a big amount of data (~800 Byte) to the DSP (the Firmware) - after that the UPS doesn't respond anymore.

--> Looks like the UPS goes to a undefinded state, if I write that big Data to Adr 0x38.

But what to do against that?

@ryf 

Hi,
UPS CAN NOT work with a high speed. Due to MCU handler and Raspberry Pi bug, you MUST decrease the I2C speed. This is the only solution for now. If not it is possible you hang up the I2C (on the MCU side). The DSP should logically work with the lower rates.

If you like I can work on the  MCU I2C routine little bit more and add some extra handlers om that.

I will be able to do that next end of the next week, as travelling to London for the Raspberry Pi Summit.

I can also release the C source to you, however, you will need much more time than me.

Any solution is fine with me. Please advise.

My Best Regards

PiM

try with 25K

BR PiM

OK - thank you

It's not the big amount of Data, even a Single Write to Adr 0x38 as attached hangs up the UPS.
What I don't understand, why does it work well if I only read from my 0x38 device but it hangs up the UPS when I write a singe Byte to the UPS...

But ok - I'll try with 25k...

Same Problem with 25k and my DSP does not work with that low Baudrate.

Look's like the two Devices are not compatible... 

If you could implement a Firmwareupgrade with a Whatchdog, that UPS Resets after it hangs up...

Thanks so much again for your absolutely great support!

@ryf 

First of all Thank you for your positive comments !

Second of all there no not compatible devices. It is up to us, and we made them compatible. Not miracles.

No one reported such bug, but it is good, because we will improve the firmware.

Yes, I add such watchdog.

The only minus is that you need to wait, until I return for the UK. So, able to work on this end of next week. 

As I see, you have I2C analyzer, so it is perfect as both have a proper tools.

We will solve it for 10000%. No miracles on this matter.

My Best Regards

PiM