The characters I see on the debug are unreadable
Even if I press the power button for 15 seconds
If you prefer, the LEDs are lit but remain fixed
Then your uart is incompatible (which vendor) or wrong mode (should be 115200 8 8n1).
I am checking the USB cable which is potentially incompatible
I use cp21x2 which works well…profilic is known to be buggy
I do not know this model
nothing to do the characters appear illogically. As if they are not correctly translated
Look this mixtures
I have put in this link two pictures that show what I have by the UART Debug port.
Without pressing the power button
Yes this looks like scrambled output of profilic usb2uart,but i have seen this only on powered device
Make sure you have connected gnd and tx to rx twice. Else try another usb2serial chipset
I am going to use this model, is it good?
I have one looking similar and it works good.
Lokal buy is much more expensive but with order in cn (ebay) you need to wait multiple weeks 
Finally it works under debian. Thanks again for your help. Now I want to be able to put PFSense (freebsd) on it and I haven’t seen anyone on the forum doing the installation would you have any idea of the right file to configure?
Thanks
Afair freebsd is not available as it does not use linux kernel.
I thought that like all other distributions Freebsd had a Linux kernel. Excuse me for my lack of knowledge but I’m trying to understand the way things work.
Openwtr is not Freebsd?
However, if I’m not mistaken, a Freebsd image is available for the R2.
I thought that too till this thread: BPI-R2 FreeBSD support/ZRouter.org support
No,openwrt is a system (afaik busybox/buildroot based) with linux kernel for router-boards
Maybe ray uploaded his current work,but hardware support was not much like linux
No, FreeBSD has own kernel. Even more Debian did version of their distro with FreeBSD kernel.
No, OpenWRT is linux based. There is set of projects for FreeBSD based routers: pfSense, freebsd-wifi-build, ZRouter.org.
Unfortunately there is nothing to test yet. Work I done for R2’s FreeBSD support is not compatible with FreeBSD HEAD and I have to do big work on conversation with other guys in project to find best way that will satisfy all of us before commit R2 support. But I’m very low on free time yet.