Ok I've installed the driver and the sketch downloads to the board most of the time. I occasionally get this error
dfu-util 0.9
Copyright 2005-2009 Weston Schmidt, Harald Welte and OpenMoko Inc.
Copyright 2010-2016 Tormod Volden and Stefan Schmidt
This program is Free Software and has ABSOLUTELY NO WARRANTY
Please report bugs to http://sourceforge.net/p/dfu-util/tickets/
Opening DFU capable USB device...
ID 0483:df11
Run-time device DFU version 011a
Claiming USB DFU Interface...
Setting Alternate Setting #0 ...
Determining device status: state = dfuERROR, status = 10
dfuERROR, clearing status
Determining device status: state = dfuIDLE, status = 0
dfuIDLE, continuing
DFU mode device DFU version 011a
DfuSe interface name: "Internal Flash "
Downloading to address = 0x08000000, size = 161408
Download [ ] 0% 0 bytes
Download [= ] 4% 7168 bytesInvalid DFU suffix signature
A valid DFU suffix will be required in a future dfu-util release!!!
Error during special command "ERASE_PAGE" get_status
Error during special command "ERASE_PAGE" get_status
The download percentage can sometimes go as high as 64% and fails with the erase page error.
If I remove the USB lead then plug it back in (LED pattern clears and a random LED lights on the board) and then hold the lead steady in the plug then the download completes and the 4 LED's do their walking pattern.
Maybe the USB socket on my board has a poor connection. I'll check it.