Thank you eureka! That is what I thought. So it would be nice if somebody could write somewhere so that there are not other people like me trying!
Attention imx_usb_loader does NOT work on Mac OS X!
So I now downloaded Kubuntu Live DVD (maybe Ubuntu would be better but I just Kubuntu until a few month ago...) and booted into it.
Thank you aditya3098 for your github and your instructions, just to be easier on freshly installed (K)Ubuntu, there was a typo (no "s" in build-essential) and a few more packages are needed: pkg-config and git
Furthermore, I still need to do "make", don't I?
Anyhow, I am in USB_download_mode:
Bus 003 Device 032: ID 15a2:0052 Freescale Semiconductor, Inc. i.MX50 SystemOnChip in RecoveryMode
However, it does not work:
imx_gui version 1.0
main:Could not open device vid=0x15a2 pid=0x52 err=-3
What does that mean and what do I have to do?