Made some changes to dxl.c to return the txrx error with Dxl.getResult().  The gbDXLtxrxStatus variable is set to 0 at start of txrx_Packet() and each COMM_ status bit is OR'd to the variable to provide most information  about communication errors.  If no errors, then gbDXLtxrxStatus is written  with only COMM_RXSUCCESS bit set (if rx succeeded, tx must have also succeeded)  to prevent breaking anything checking for only COMM_RXSUCCESS bit (mostly older programs).
All other functions return the usual 1 (success) or 0 (failure).
Finally got around to testing the attempt to port the arbotix's BioloidController interpolating motion engine over to the CM-9.  The example should work and the library appears to work correctly, but needs more testing to be sure it is actually writing to FLASH and not storing to RAM.
Also need to modify the RoboPlus Motion file converter to create BioloidController header files compatible with the CM-9 version.  The arbotix is AVR based, so it requires special functions to read from FLASH memory, while the STM32 appears to need only the address/pointer to read (attempts to write in a program will cause a crash).