I just submitted a series of 7 patches for the ft245r.c (ftdi_syncbb)
The main objective of this patch series was to add TPI support such that
chips like the ATtiny9 etc can be programmed using an FTDI cable (we happen
to use the 5 volt version of the TC2030-FTDI-TTL-232R, but with the right
connector, FTDI cable TTL-232RG-VSW5V can be used).
However, as it stood, just adding TPI support gave an excruciatingly slow
programming speed. It was bad on Linux and even worse on Windows (taking
well over a minute to program 1KiB of flash!).
With these patches, programming time is down to 2.6 seconds on Linux and
about 5.2 seconds on Windows (on an old laptop running Windows 8). This
assumes running at max baudrate (-b750000). The default baudrate is 150000
so that will be considerable slower, but seems to be a safe default.
The last patch in this series adds support for the FTDI D2XX driver. I
didn't see much difference in performance between D2XX and libftdi1 for
Windows, but from what I can see, it's far easier to install the D2XX
driver, so I think this is a useful option to have.
For convenience, I created a GIT repository that has all the patches I
submitted so far: