In some cases checkm8 does not work directly through Bonobo. This is due to the fact that checkm8 is a timing based exploit and the combination of python/libusb and the Bonobo USB hub does not get the timing right and fails.
Try using this C/C++ checkm8 demote version instead:
LED is red¶
Red LED means USB overcurrent condition. Disconnect the target phone and the Bonobo cable from the PC. Replugging the cable should fix the problem.
If the problem persists and the LED becomes red as soon as the cable is powered, make sure you are using the right FPGA bitstream for your cable serial number. Refer to Firmwares for flashing instructions.
Bulk read/write failed¶
In case of “Bulk read failed” and “Bulk write failed” messages from OpenOCD when dumping the bootrom or reading other chunks of memory:
> dump_image bootrom.bin 0x100000000 0x20000 Bulk read failed Bulk write failed Bulk write failed Failed to read memory and, additionally, failed to find out where Info : dropped 'telnet' connection
Update the FPGA bitstream to the latest version as explained in Bitstream (FPGA).