Bei mir kam soeben etwas an ...

 [2014-12-08 10:46:38] bfx_open: Failed to open
 [2014-12-08 10:46:42] bfx_open: Failed to open
 [2014-12-08 10:51:40] bfx_open: Failed to open
 [2014-12-08 10:51:43] bfx_open: Failed to open

Are you using any usb hub? Try to plug it directly to Rpi.
Did Rpi use same power source with miner?
Try to change the usb cable.
Clean the board from dirt then visual check the component.

cgminer version 4.4.2 - Started: [2014-12-07 14:17:00]
--------------------------------------------------------------------------------
 (5s):0.000 (1m):0.000 (5m):0.000 (15m):0.000 (avg):0.000h/s
 ST: 3  SS: 0  NB: 8  LW: 653  GF: 1  RF: 0
 Connected to miner-control.de diff 16 with stratum as user NTYNy7JWo1LyK9Z51ZxdcpsdzEpfT5C6VV
 Block: 2e05d06d...  Diff:1.01M  Started: [14:33:59]  Best share: 0
--------------------------------------------------------------------------------
 USB management Pool management Settings Display options Quit
 2: HEX8 2  : 220  850/ 800mV  | A:0 R:0/0.00% HW:0/0.00%
--------------------------------------------------------------------------------
 [2014-12-07 14:17:00] Pool 1 difficulty changed to 16
 [2014-12-07 14:17:00] Network diff set to 1.07M
 [2014-12-07 14:17:05] API running in IP access mode on port 4029 (11)
 [2014-12-07 14:19:59] Network diff set to 1.03M
 [2014-12-07 14:19:59] Stratum from pool 0 detected new block
 [2014-12-07 14:23:22] Network diff set to 1.02M
 [2014-12-07 14:23:22] Stratum from pool 0 detected new block
 [2014-12-07 14:23:36] Network diff set to 1.03M
 [2014-12-07 14:23:36] Stratum from pool 0 detected new block
 [2014-12-07 14:25:26] Network diff set to 1.05M
 [2014-12-07 14:25:26] Stratum from pool 0 detected new block
 [2014-12-07 14:26:08] Network diff set to 1.05M
 [2014-12-07 14:26:08] Stratum from pool 0 detected new block
 [2014-12-07 14:27:08] Stratum connection to pool 0 interrupted
 [2014-12-07 14:27:08] Pool 0 difficulty changed to 16
 [2014-12-07 14:30:03] Network diff set to 1.03M
 [2014-12-07 14:30:03] Stratum from pool 0 detected new block
 [2014-12-07 14:33:59] Network diff set to 1.01M
 [2014-12-07 14:33:59] Stratum from pool 0 detected new block
[2014-12-07 14:34:04] HEX8 0 failure, disabling!
 [2014-12-07 14:34:24] Hotplug: hexminer8 added HEX8 1
 [2014-12-07 14:34:37] HEX8 1 failure, disabling!
 [2014-12-07 14:34:50] Hotplug: hexminer8 added HEX8 2

"hexminer8-set-diff-to-one" : "0",
"hexminer8-chip-mask" : "255",
"hexminer8-voltage"  : "850",
"hexminer8-options" : "8:220",
"set_default_to_8" : true

[2014-12-07 14:25:04] Started cgminer 4.7.1
 [2014-12-07 14:25:04] Loaded configuration file /home/pi/cgminer.conf
 [2014-12-07 14:25:04] Invalid --usb DRV:limit missing ':'

I'm not familiar with the bfx settings, but

Try this:

bfgminer version 5.0.0 - Started: [2014-12-07 10:01:14] - [  0 days 00:02:02]
 Manage devices Pool management Settings Display options         Help Quit
 Pool 1: mint.bitminter.com  Diff:16  +Strtm  LU:[10:03:10]  User:Buchinger84.Buchi
 Block #333250: ...11a7df35  Diff:40G (286.4P)  Started: [10:03:08]  I:15.22uBTC/hr
 ST:21  F:0  NB:4  AS:0  BW:[101/ 62 B/s]  E:86.32  BS:746
 10/18        | 37.91/34.76/33.89Gh/s | A:50 R:1+0(2.0%) HW:25/2.6%
---------------------------------------------------------------------------------------
 AMU 0:       |  2.16/ 2.16/ 2.15Gh/s | A: 4 R:0+0(none) HW: 0/none
 AMU 1:       |  2.22/ 2.20/ 2.54Gh/s | A: 5 R:0+0(none) HW: 0/none
 BFX 0:       |  4.03/ 3.69/ 3.52Gh/s | A: 4 R:0+0(none) HW: 1/.99%
 BFX 1:       |  4.42/ 4.10/ 3.77Gh/s | A: 4 R:0+0(none) HW: 1/.93%
 BFX 2:       |  4.01/ 3.70/ 3.04Gh/s | A: 9 R:0+0(none) HW: 0/none
 BFX 3:       |  4.16/ 3.84/ 3.37Gh/s | A: 7 R:1+0( 12%) HW: 0/none
 BFX 4:       |  3.91/ 3.58/ 3.40Gh/s | A: 3 R:0+0(none) HW: 1/1.0%
 BFX 5:       |  4.28/ 3.88/ 4.73Gh/s | A: 7 R:0+0(none) HW: 2/1.5%
 BFX 6:       |  4.11/ 3.80/ 3.94Gh/s | A: 4 R:0+0(none) HW: 2/1.8%
 BFX 7:       |  4.66/ 4.21/ 3.69Gh/s | A: 6 R:0+0(none) HW:18/ 15%
---------------------------------------------------------------------------------------
 [1970-01-01 01:00:33] bfx_open: Failed to open --> ??

[2014-12-07 00:35:47] Coinbase check: multiple inputs in coinbase: 0xb3
 [2014-12-07 00:35:47] Pool 0 misbehaving (coinbase check), disabling!
 [2014-12-07 00:36:09] Coinbase check: multiple inputs in coinbase: 0xef

All I can say is your OS appears to be broken.

]
,
"api-listen" : true,
"api-port" : "4028",
"api-allow" : "W:0/0",
"expiry" : "120",
"failover-only" : true,
"log" : "5",
"no-pool-disable" : true,
"queue" : "2",
"scan-time" : "60",
"worktime" : true,
"shares" : "0",
"kernel-path" : "/usr/local/bin",
"scan" : ["antminer:all"],
"set-device" : ["antminer:clock=x0A81"],
"scan" : ["bfx:all"],
"set-device" : ["bfx:osc6_bits=53"]
}

There is a README file.

See any operating system documentation about shared libraries for
more information, such as the ld(1) and ld.so( manual pages.
----------------------------------------------------------------------
 /bin/mkdir -p '/usr/local/share/doc/libbase58'
 /usr/bin/install -c -m 644 AUTHORS COPYING README '/usr/local/share/doc/libbase58'
 /bin/mkdir -p '/usr/local/include'
 /usr/bin/install -c -m 644 libbase58.h '/usr/local/include'
 /bin/mkdir -p '/usr/local/lib/pkgconfig'
 /usr/bin/install -c -m 644 libbase58.pc '/usr/local/lib/pkgconfig'
make[3]: Leaving directory `/usr/src/bfgminer/libbase58'
make[2]: Leaving directory `/usr/src/bfgminer/libbase58'
Making install in libblkmaker
make[2]: Entering directory `/usr/src/bfgminer/libblkmaker'
  CC       libblkmaker_jansson_0.1_la-blkmaker_jansson.lo
blkmaker_jansson.c:13:21: error: jansson.h: No such file or directory
blkmaker_jansson.c:21:3: error: #error "Jansson 2.0 with long long support required!"
blkmaker_jansson.c:24: error: expected '=', ',', ';', 'asm' or '__attribute__' before '*' token
blkmaker_jansson.c:130: error: expected declaration specifiers or '...' before 'json_t'
blkmaker_jansson.c: In function 'parse_txn':
blkmaker_jansson.c:131: error: 'json_t' undeclared (first use in this function)
blkmaker_jansson.c:131: error: (Each undeclared identifier is reported only once
blkmaker_jansson.c:131: error: for each function it appears in.)
blkmaker_jansson.c:131: error: 'vv' undeclared (first use in this function)
blkmaker_jansson.c:133: warning: implicit declaration of function 'json_object_get'
blkmaker_jansson.c:133: error: 'txnj' undeclared (first use in this function)
blkmaker_jansson.c:133: warning: implicit declaration of function 'json_is_string'
blkmaker_jansson.c:135: warning: implicit declaration of function 'json_string_value'
blkmaker_jansson.c: At top level:
blkmaker_jansson.c:174: warning: type defaults to 'int' in declaration of 'json_t'
blkmaker_jansson.c:174: error: expected ';', ',' or ')' before '*' token
blkmaker_jansson.c:280: error: expected '=', ',', ';', 'asm' or '__attribute__' before '*' token
blkmaker_jansson.c:325: error: expected '=', ',', ';', 'asm' or '__attribute__' before '*' token
blkmaker_jansson.c:374: error: expected '=', ',', ';', 'asm' or '__attribute__' before '*' token
blkmaker_jansson.c:378: error: expected '=', ',', ';', 'asm' or '__attribute__' before '*' token
make[2]: *** [libblkmaker_jansson_0.1_la-blkmaker_jansson.lo] Error 1
make[2]: Leaving directory `/usr/src/bfgminer/libblkmaker'
make[1]: *** [install-recursive] Error 1
make[1]: Leaving directory `/usr/src/bfgminer'
make: *** [install] Error 2
root@sunwatch:/usr/src/bfgminer#

root@sunwatch:~# sudo apt-get install libjansson-dev
Reading package lists... Done
Building dependency tree
Reading state information... Done
E: Unable to locate package libjansson-dev

root@sunwatch:/usr/src# dpkg -i libjansson-dev_2.7-1_armel.deb
Selecting previously deselected package libjansson-dev.
(Reading database ... 30542 files and directories currently installed.)
Unpacking libjansson-dev (from libjansson-dev_2.7-1_armel.deb) ...
dpkg: dependency problems prevent configuration of libjansson-dev:
 libjansson-dev depends on libjansson4 (= 2.7-1); however:
  Package libjansson4 is not installed.
dpkg: error processing libjansson-dev (--install):
 dependency problems - leaving unconfigured
Errors were encountered while processing:
 libjansson-dev

root@sunwatch:~# apt-get install uthash-dev
Reading package lists... Done
Building dependency tree
Reading state information... Done
uthash-dev is already the newest version.
0 upgraded, 0 newly installed, 0 to remove and 0 not upgraded.

configure: error: Could not find HASH_ITER - please install uthash-dev 1.9.4+

root@sunwatch:/usr/src# apt-get install bfgminer
Reading package lists... Done
Building dependency tree
Reading state information... Done
E: Unable to locate package bfgminer

cgminer version 4.4.2 - Started: [2014-12-06 11:59:35]
--------------------------------------------------------------------------------
 (5s):0.000 (1m):168.9M (5m):3.229G (15m):2.438G (avg):3.443Gh/s
 A:784  R:0  HW:0  WU:49.1/m
 Connected to miner-control.de diff 16 with stratum as user
 Block: d970747b...  Diff:1.08M  Started: [12:14:40]  Best share: 863
--------------------------------------------------------------------------------
 USB management Pool management Settings Display options Quit
 4: HEX8 4  : 220  850/ 800mV  |  0.000 /  0.000h/s WU:  0.0/m
--------------------------------------------------------------------------------
 [2014-12-06 12:05:21] HEX8 0 failure, disabling!
 [2014-12-06 12:06:42] HEX8 1 failure, disabling!
 [2014-12-06 12:06:57] HEX8 2 failure, disabling!
 [2014-12-06 12:09:33] HEX8 3 failure, disabling!