Cannot boot beaglebone black from SD card with images generated by BuildRoot

[Axel Munt]

Hello
Fedora 20
I have downloaded latest version of Buidroot 2015.08.01 and generated boot files and root image like so

$ make beaglebone_defconfig   // BeagleBlak options defined , in particular target
$ make menuconfig                 // Edit a few options (added C++)
$ make

Got the expected tree
  output/images/
  ├── am335x-boneblack.dtb
  ├── am335x-bone.dtb
  ├── MLO
  ├── rootfs.ext2
  ├── u-boot.img
  ├── uEnv.txt
  └── zImage

Partitioned 8Gb SDcard  
- partition 1 : W95 FAT32 bootable (~78 MB
- partition 2 : Linux (remaining space ~ 7 GB)

I then boot by maintaining boot button (S2) pressed while powering up Beaglebone
Leds start flashing, some gibberish (2/3 lines) appears on serial line,
and I cannot access the BeagleBoard

Can anyone help

[Axel Munt]

I found may mistake if one can talk of mistake :
the serial line baud rate is 115200 and I was I was using it at 9600
So at best I saw gibberish

Lost two precious days