Important to know that 8 is not supported.

f75fac8d · Wesley W. Terpstra · eb613b05 · f75fac8d
Commit f75fac8d authored 13 years ago by Wesley W. Terpstra
--- a/api/FEATURES
+++ b/api/FEATURES
  Support for posix/win32/lm32
+  Support for 16/32/64 bit processors
  Simultaneous master and slave operation
    - user can attach software devices to bus
  Maximum bus width autonegotiation (8/16/32/64)