Solved. Confirmed by Regional DELL support. DELL PowerEdge R640 can not use BOSS-S1 card in singleCPU configuration. Regards.
Hello! I've try to install BOSS-S1 card (with 2x240 SSD M2 installed) into R640 server with single CPU Gold 6242R. Risers A1 and A2 are preinstalled. If I install a card in slot3, nothing happens, but it should be, in a uniprocessor configuration slot3 does not work. However, the device is detected in the hardware inventory. If I install a card in slot1 or slot2, then the boot stops abnormally with the messages: UEFI0056: A PCIe error has occured. Check the System Event Log (SEL) to identify the PCIe device that is not functioning correctly, and then update the device firmware. And there is no card in the hardware inventory. At first, I assumed that the card was faulty, or it had a firmware failure. But, having installed in another server (R440), I found that the card is normally detected and, even, updates the firmware via iDRAC.  Then I just installed 2 bronze processors in the R640 server and the card was detected and worked in any PCIe slot (1,2.3).  So, my question is subject. Or maybe a different set of risers is required for the correct operation of this card in a uniprocessor configuration? Regards!
Does R640 can use BOOS-S1 card in 2 CPU config only?