This is because of cache. 0x40000000 bit means uncahed memory...
Did i get it right: SD card sends data directly to DRAM, and it is being later overwritten by data flushed from the CPU cache (if any)?
ok, I have managed to start an encoded DISKBOOT.BIN (a simplisitic blinker so far) from a freshly formatted SD card but only with '#' spamming, hardware loopback never worked, it always stopped on '#' sign for me.
thank you very much for the help!