This is a compact and universal MSP430 USB CDC driver. Every effort has been made to make it portable.

1. Initialising the USB hardware on the RP2040.
2. Receiving and responding to setup packets from the host (PC). This determines which driver the OS will load.
3. If the host is satisfied with the setup, then sending and receiving data packets may start.
   
   
   

   Pseudo code

DEFINE DEVICE-DECRIPTOR \ Device descriptor (18 bytes)
12 c, 01 c, 10 c, 01 c, ( 1.10 ) EF c, 02 c, 01 c, 40 c, 66 c, 66 c, ( 6666 )
10 c, 66 c, ( 6610 ) 00 c, 01 c, ( vsn 1.00 ) 00 c, 02 c, 00 c, 01 c,  align

DEFINE CONFIGURATION-DESCRIPTOR \ Configuration descriptor (9 or 75 bytes)
9 c,  2 c,  4B c,  0 c,  2 c,  1 c,  0 c,  80 c,  FA c, \ Maximum power = 500mA
8 c,  0B c,  0 c,  2 c,  2 c,  2 c,  1 c,  0 c,         \ Interface Association Descriptor - CDC 0
9 c,  4 c,  0 c,  0 c,  1 c,  2 c,  2 c,  1 c,  0 c,    \ Interface 1: Control - 1 - 0 -
5 c,  24 c,  0 c,  10 c,  1 c, ( CDC vsn 1.10 )         \ CDC Header functional
5 c,  24 c,  1 c,  0 c,  1 c,                           \ CDC Call management functional
4 c,  24 c,  2 c,  2 c,                                 \ CDC ACM functional ( two commands )
5 c,  24 c,  6 c,  0 c,  1 c,                           \ CDC Union functional ( one interface )
7 c,  5 c,  81 c,  3 c,  8 c,  0 c,  10 c,              \ Endpoint 1 IN descriptor
9 c,  4 c,  1 c,  0 c,  2 c,  0A c,  0 c,  0 c,  0 c,   \ Interface 2: DATA
7 c,  5 c,  82 c,  2 c,  40 c, 0 c,  0 c,               \ Endpoint 2 IN descriptor
7 c,  5 c,  3 c,  2 c,  40 c, 0 c,  0 c,  align         \ Endpoint 3 OUT descriptor