en:pfw:usb_cdc_driver_for_rp2040
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Table of Contents
USB CDC driver for RP2040
The idea
This is a compact and universal MSP430 USB CDC driver. Every effort has been made to make it portable.
What we need to do in short
- Initialising the USB hardware on the RP2040.
- Receiving and responding to setup packets from the host (PC). This determines which driver the OS will load.
- If the host is satisfied with the setup, then sending and receiving data packets may start.
Pseudo code
hex Function: DEVICE-DECRIPTOR \ 18 bytes The USB CDC device descriptor Function: CONFIGURATION-DESCRIPTOR \ 9 or 75 bytes The complex USB CDC device descriptor Function: USB-STATE ( -- a ) Hold current USB state in first half word: 3 = ready In second half word are memory for the 900/880 requests The English/US language ID string CDC Line data: 115k2, Stop bits, Parity, Data bits Function: START-USB ( -- ) Initialise the RP2040 USB hardware, restart the USB hardware, erase the USB DPRAM, enable USB controller, set USB address to zero. Setup used endpoints and used interrupts & enable full speed USB. Function: PAD ( -- a ) Reserve 64 bytes RAM as scratchpad area Function: EP0 ( -- a ) Function: EP1 ( -- a ) Function: EP2 ( -- a ) Function: EP3 ( -- a ) Seven cells data structures to control endpoint-0, 1, 2 & 3 The first four cells a variable data The three cells thereafter contain USB pointers & register addresses Function: @VAL ( -- +n ) Read the wValue from any eight bytes setup packet Function: @LEN ( -- +n ) Read the wLength from any eight bytes setup packet Function: >UNI ( a1 u -- a2 ) Store the ASCII string to a unicode string tailored for USB Function: >CNT \ Offset 00 Function: >ORG \ Offset 04 Function: >PKT \ Offset 08 Function: >PID \ Offset 12 Function: >ICTRL \ Offset 16 Function: >OCTRL \ Offset 20 Function: >BUF \ Offset 24 Seven functions that calculate the address of each field in the endpoint data structures Function: EP-IN ( ep -- org buf pkt ) Calculate data to send for 'ep' x Function: PREPARE ( a u ep -- ) Prepare data packet from address 'a' with the length 'u' to send tp 'ep' x Function: >NEXT ( ep -- pkt ) Get next packet size for 'ep' x, when 'pkt' is zero there is no more data to send Function: !PKT ( pkt ep -- ictrl ) Store next packet to send for 'ep' x Function: PREP-RCV ( ep -- ) Enable endpoint 'ep' x to receive a data packet Function: GONE? ( ep -- f ) Leave true when the data in 'ep' x was sent Function: USB? ( -- +n ) Leave three when the host & device are connected ...
Implementation example
\ This program assumes 32-bit cells.
\ Non standard words used are:
\ : C@+ ( a1 -- a2 b ) count ;
\ : H@ ( a -- h ) count swap c@ 8 lshift or ;
\ : H! ( h a -- ) >r dup r@ c! 8 rshift r> 1+ c! ;
\ : @+ ( a1 -- a2 x ) >r r@ cell+ r> @ ;
\ : **BIS ( msk a -- ) >r r@ @ or r> ! ;
\ : **BIC ( msk a -- ) >r invert r@ @ and r> ! ;
\ : **BIX ( msk a -- ) >r r@ @ xor r> ! ;
\ : BIT** ( msk a -- b ) @ and ;
hex \ USB device data structures
create DEV-DESCR \ 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
create CONFIG-DESCR \ 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
create PAD ( -- a ) 40 allot \ Scratchpad memory
decimal
create USB-STATE 0 , \ Hold current USB state: 3 = ready
\ Second half word for 900/880 requests
4 c, 3 c, 9 c, 4 c, \ English/US = language ID
115200 , 0 c, 0 c, 8 c, \ Line data: 115k2, Stop bits, Parity, Data bits
align hex
: START-USB ( -- )
1000000 4000C000 \ Bit-24 mask & Reset register
2dup **bis 2dup **bic \ Restart USB
begin 2dup 8 + bit** until \ Wait until USB is ready
2drop 50100000 1000 false fill \ Erase USB ram
00000009 50110074 ! \ USB_USB_MUXING Softcon, to PHY
0000000C 50110078 ! \ USB_USB_PWR VBUS overide & detect enable
00000001 50110040 ! \ USB_MAIN_CTRl Enable controller
20000000 5011004C ! \ USB_SIE_CONTROL Enable End Point 0 interrupt
false 50110000 ! \ Respond to address 0 on initial setup
00011010 50110090 ! \ USB_INTE Enable 3 interrupts
AC000180 50100008 ! \ init COMM endpoint in buffer 1
A8000200 50100010 ! \ init SEND endpoint in buffer 2
A8000280 5010001C ! \ init RECV endpoint out buffer 3
00010000 5011204C ! ; \ USB_SIE_CONTROL Enable pull up
\ Endpoint data structures, 4 variable cells & 3 constant cells
\ Name: CNT ORG PKT PID INBUF-CTRL OUTBUF-CTRL EPxBUF
\ Offsets: 00 04 08 0C 10 14 18
create EP0 4 cells allot 50100080 dup , 4 + , 50100100 ,
create EP1 4 cells allot 50100088 dup , 4 + , 50100180 ,
create EP2 4 cells allot 50100090 dup , 4 + , 50100200 ,
create EP3 4 cells allot 50100098 dup , 4 + , 50100280 ,
: @VAL ( -- +n ) 50100002 h@ ; \ wValue
: @LEN ( -- +n ) 50100006 h@ ; \ wLength
: >UNI ( a1 u -- a2 ) \ Convert string to unicode format for USB
dup 2* 302 + pad h! 0 \ String length & notifier
?do c@+ pad i 2* + 2 + h! loop drop pad ;
\ Addresssing tools for the endpoint data structures
: >CNT ; immediate \ 00 - ep0 >cnt ! - Bytes left te send
: >ORG cell+ ; \ 04 - ep1 >org @ - Address of next packet
: >PKT 2 cells + ; \ 08 - Packet size
: >PID 3 cells + ; \ 0C - Actual PID
: >ICTRL 4 cells + ; \ 10 - USB in control register
: >OCTRL 5 cells + ; \ 14 - USB out control register
: >BUF 6 cells + ; \ 18 - EPx buffer address
\ Primitive endpoint functionality
: EP-IN ( ep -- org buf pkt ) \ Calculate data to send for EPx
>r r@ >org @ r@ >buf @ r> >pkt @ ;
: PREPARE ( a u ep -- ) \ Prepare data to send for EPx
>r dup r@ >cnt ! 40 min r@ >pkt ! r> >org ! ;
: >NEXT ( ep -- pkt ) \ Get next packet size for EPx
>r r@ >pkt @ r@ >org @ + r@ >org !
r@ >pkt @ r@ @ over - dup r@ ! 40 min r> >pkt ! ;
: !PKT ( pkt ep -- ictrl ) \ pid + pkt + mask - Store next packet to send for EPx
>r r@ >pid @ or 8000 or r> >ictrl @ tuck ! ;
: PREP-RCV ( ep -- ) \ Prepare to receive a packet on EPx
>r r@ >octrl @ r@ >pid @ 40 or over !
2000 r> >pid **bix 400 swap **bis ;
: GONE? ( ep -- f ) >ictrl @ @ 400 and 0= ; \ Leave true when Epx packet was sent
: USB? ( -- +n ) usb-state h@ 3 = ; \ True when host & device are connected
\ Basic receive & transmit packet handlers
: USB-SEND ( ep -- ) >r r@ >next r@ !pkt 2000 r> >pid **bix 400 swap **bix ;
: USB-RCV ( pid ep -- ) tuck >pid ! prep-rcv ;
: BUS-RESET ( -- )
80000 50113050 ! \ SIE_STATUS - BUS_RESET (Clear bit)
false 50110000 ! false usb-state ! \ USB-address=0 & USB-state=0, u-config = 0
false ep3 usb-rcv false ep2 >pid ! ; \ Allow receiving EP3 & init. transmit EP2
: SETUP> ( a u -- ) \ Handle the answer for all setup packages
2000 ep0 >pid ! ep0 prepare \ Start with DATA1, setup packet data
begin
ep0 ep-in move ep0 usb-send \ Store & send packet
1 50110058 \ Packet gone?
begin 2dup bit** until **bis
ep0 @ 0= until 2000 ep0 usb-rcv ; \ Handle ZLP
: XTABLE ( +n "name" -- ) \ Define custom execution table
create ,
does> @+ ( req -- )
>r r@ for 2dup @ = if \ Token found?
nip rdrop r> cells + \ Yes, calc. cell with XT
@ execute exit \ Fetch & execute XT
then
cell+
next rdrop 2drop \ No token found
1 5011,0068 ! 800 5010,0080 ! ; \ Send EP0 stall
: ZLP> ( -- ) here false setup> ; \ Send EP0 ZLP
:noname me count 1D min >uni dup c@ @len min setup> ; \ 0302 Device name string
:noname usb-state cell+ 4 setup> ; \ 0300 Lang-ID string
:noname config-descr @len 4B min setup> ; \ 0200 Config descriptor
:noname dev-descr @len 12 min setup> ; \ 0100 Device descriptor
4 xtable HANDLE-SETUP ( req -- )
0100 , 0200 , 0300 , 0302 ,
( dev ) , ( conf ) , ( 300 ) , ( 302 ) ,
:noname @val usb-state c! zlp> ; \ 2221 Set control line state
:noname usb-state cell+ cell+ 7 setup> ; \ 21A1 Get line coding
:noname 2000 ep0 usb-rcv zlp> ; \ 2021 Set line coding
:noname zlp> @val usb-state 2 + h! ; \ 0900 Set USB configuration
:noname usb-state 2 + 2 setup> ; \ 0880 Get USB configuration
:noname @val handle-setup ; \ 0680 Basic usb SETUP handler
:noname zlp> @val 5011,0000 ! ; \ 0500 Set device address
7 xtable HANDLE-REQ) ( -- )
0500 , 0680 , 0880 , 0900 , 2021 , 21A1 , 2221 ,
, , , , , , ,
: HANDLE-REQ ( -- ) 20000 5011,3050 ! 5010,0000 h@ handle-req) ;
\ Ring buffer structure for serial I/O
\
\ 0 = Number of used storage units (CNT)
\ 1 = In pointer (IN)
\ 2 = Out pointer (OUT)
\ 3 = Start of ring buffer
100 constant #L \ Buffer size
#L 1- constant #R \ Buffer mask
50100300 constant BUFFER1 \ Usess 2 * #L + 24 bytes = 536 bytes
buffer1 #l + 3 cells + constant BUFFER2 \ Start of out buffer
: #RX ( -- +n ) buffer1 @ ; \ +n characters in receive buffer
: #TX ( -- +n ) buffer2 @ ; \ +n characters in send buffer
: >RX ( ch -- )
buffer1 cell+ >r
r@ @ r@ 2 cells + + c! \ Yes, add char to buffer
r@ @ 1+ #r and r@ ! \ Increase & protect write pointer
1 r> cell- +! ; \ Increase used space
: RX> ( -- ch )
buffer1 2 cells + >r
r@ @ r@ cell+ + c@ \ Read char. from buffer
r@ @ 1+ #r and r@ ! \ Increase & protect read pointer
true r> 2 cells - +! ; \ Decrease used space
: >TX ( ch -- )
buffer2 cell+ >r
r@ @ r@ 2 cells + + c! \ Yes, add char to buffer
r@ @ 1+ #r and r@ ! \ Increase & protect write pointer
1 r> cell- +! ; \ Increase used space
: TX> ( -- ch )
buffer2 2 cells + >r
r@ @ r@ cell+ + c@ \ Read char. from buffer
r@ @ 1+ #r and r@ ! \ Increase & protect read pointer
true r> 2 cells - +! ; \ Decrease used space
0 value IFLAG
: ENDPOINTS ( -- ) \ Handle used endpoints
50110058 @ >r
r@ 04 and if zlp> then \ EP1 active?
iflag r@ 80 and or to iflag \ EP3 active, remember
r> 50110058 ! ;
: REQUESTS ( -- ) \ Handle all USB requests
50110098 @ >r ( ints )
r@ 10 and if endpoints then \ 10 = #04 bitmask
r@ 1000 and if bus-reset then \ 1000 = #12 bitmask
r> 10000 and if handle-req then ; \ 10000 = #16 bitmask
: USB-HANDLER ( -- ) \ Handle USB setup & character I/O
requests
iflag if \ Next RX packet wanted?
#L #tx - 40 > \ Yes, enough space in TX buffer?
#L #rx - 40 > and if \ And next RX packet fits too?
ep3 >buf @ 5010009C c@
0 ?do c@+ >rx loop \ Yes, fill RX buffer
drop false to iflag \ Done
ep3 prep-rcv \ And allow next RX packet
then
then
usb? if \ Still connected?
#tx if \ EP2 Any chars to send?
ep2 gone? if \ Yes, previous packet gone?
ep2 >buf @ #tx 40 umin \ Packet place & size
2dup ep2 prepare bounds \ Init. transmit pointers
?do tx> i c! loop \ Place data in EP2-buffer
ep2 usb-send \ Send to host
then
then
then ;
: USB-KEY? ( -- f ) usb-handler #rx ; \ KEY & EMIT with ringbuffer
: USB-KEY ( -- c ) begin usb-handler #rx until rx> ;
: USB-EMIT ( c -- ) begin usb-handler #L #tx - until >tx ;
: USB-ON ( -- )
50100300 [ #L 2* 6 cells + ] literal false fill \ Init. buffer space to zero
start-usb false usb-state ! false to iflag
['] usb-key? to 'key? \ Install USB CDC char. I/O vectors (noForth specific!)
['] usb-key to 'key
['] usb-emit to 'emit ;
usb-on
en/pfw/usb_cdc_driver_for_rp2040.1766843193.txt.gz · Last modified: 2025-12-27 14:46 by willem