UM10912 / Table 935 / DEVCMDSTAT shows that USB1 device controller can enumerate at either FS or HS.
DEVCMDSTAT ::[23:22] Speed (01b FS, 10b HS)
However this field is read only. How can I force USB1 to only enumerate at FS ? . i.e. decline high speed handshaking to expose itself as FS capable device only to the host.