Manually specify available modules and disable any modules
that are currently unsupported on the litex target.
Signed-off-by: Sean Cross <sean@xobs.io>
The SPI flash on current Fomu firmware is slow. Circuitpython runs
XIP from SPI flash, and so execution time can also be slow. Ordinarily
this isn't a problem, however certain operations are time-sensitive.
In particular, USB function needs to be handled quickly in order to
prevent the host from re-enumerating the device.
Place several critical TinyUSB structures into RAM, as well as several
hot functions that are frequently called. This reduces execution time
at the expense of system memory, and greatly improves system stability.
Signed-off-by: Sean Cross <sean@xobs.io>
