Windows and Linux host during enumeration requests device
descriptor with request size set to 64 bytes when device
was in default state (no address).
Those systems do not want 64 bytes though since usb descriptors is
only 18 bytes long so they silently expect that only one packet
will be received possibly 18 bytes for EPS > 16 or 8 or 16 bytes
for smaller EP0.
For devices with CFG_TUD_ENDPOINT0_SIZE size 8 or 16 there was
workaround that reduced request size to CFG_TUD_ENDPOINT0_SIZE
and that was enough to satisfy Windows and Linux hosts.
However USBCV testing application also requests device descriptor
but with size set to 18 bytes. Workaround for Window/Linux
prevented USBVC to tests devices with 8 bytes EP0 size since it
send only 8 bytes while application did wanted 18 bytes.
Solution that satisfies both cases it to check if in default state device
descriptor request wants more bytes than descriptor size (18).
If so host is expecting to receive less bytes then requested
and workaround would be applied since Linux/Windows only try
to read one packet.
If 18 bytes was requested as is the case for USBCV, core returns
descriptor in 2 or 3 packets as application expects.
Note: this commit does not change any logic.
xfer_ctl_t structure keeps all dynamic data connected with transfer.
It used to have pointer to register set that was constant and was there
for convenience only.
Removing register pointer from structure makes cleanup easier as whole
structure can be erased with memset like function.
In many cases functions were using local variable regs and xfer->regs which
were same, that could be confusing so this part is unified.
Few macros were added for easy conversion between epnum, xfer, and regs.
DA146xx are Bluetooth devices that may be battery
powered and when not connected to USB host there
is no need for USB peripheral to be running.
This change allows to enable USB peripheral when
VBUS is present otherwise USB is down reducing
power consumption.
tud_vsub_changed() function must be called
whenever VBUS change was detected.
For bus-powered devices this function should be called
at startup since VBUS must be present while device
is working.
hathach