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--- en:pfw:usb_cdc_driver_for_rp2040 [2025-12-27 13:58] – [Pseudo code] willem
+++ en:pfw:usb_cdc_driver_for_rp2040 [2026-01-13 18:16] (current) – [The idea] willem
@@ Line 37: / Line 37: @@
 Reserve 64 bytes RAM as scratchpad area
-Function: EP0
+Function: EP0   ( -- a )
-Function: EP1
+Function: EP1   ( -- a )
-Function: EP2
+Function: EP2   ( -- a )
-Function: EP3
+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
+Function: USB-SEND ( ep -- )
+Transmit the prepared data packet to 'ep' x
+Function: USB-RCV  ( pid ep -- )
+Enable the receiving of a data packet on 'ep' x starting with the 'pid'
+from the stack
+Function: BUS=RESET ( -- )
+Handle a USB bus reset, clearing the device address to zero, the USB
+state to zero, reinitialise the receiving & transmitting endpoints
+Function: SETUP>   ( a u -- )
+Handle the answer data  packet 'a' 'u' for all setup packages
+When done wait for a ZLP from the host to signal a correct answer
+Function: XTABLE
+    Define an execution table entry for '+n' request actions
+    Define:  ( +n "name" -- )
+        Create a table with "name" for '+n' actions
+    Action:  ( request -- )
+        Execute the action for 'request' or generate a stall
+        when the 'request' is not available
+Function: ZLP>     ( -- )
+Send a zero length package through endpoint zero. This is used
+to signal the handling of a request that sends no data back
+Define four action in front that leave their execution tokens on the stack
+action xt
+action xt
+action xt
+action xt
+Function: HANDLE-SETUP ( req0 .. req3 4 -- )
+action xt
+A1 action xt
+action xt
+action xt
+action xt
+action xt
+action xt
+Function: HANDLE-REQ)  ( req0 .. req6 7 -- )
+Function: HANDLE-REQ   ( -- )
+Reset setup request interrupt, read bmrequest type and do HANDLE-REQ)
+Function: #L           ( -- +n )
+Ring buffer size, must be a power of two
+Function: #R           ( -- +n )
+this is equal to #L - 1
+Function: #RX          ( -- +n )
+Leave number of characters in receive buffer
+Function: #TX          ( -- +n )
+Leave number of characters in transmit buffer
+Function: >RX          ( c -- )
+Store character 'c' in RX ring buffer
+Function: >TX          ( c -- )
+Store character 'c' in TX ring buffer
+Function: RX>          ( -- c )
+Read character 'c' from RX ring buffer
+Function: TX>          ( -- c )
+Read character 'c' from TX ring buffer
+Function: IFLAG
+Reserve one cell space for receive interrupt flag
+Function: ENDPOINTS    ( -- )
+Handle EP1 & EP3 endpoints, save received data interrupt flag in IFLAG
+Release all interrupt flags
+Function: REQUESTS     ( -- )
+Handle all USB interrupts, that are the USB bus reset, setup requests & endpoints
+Function: USB-HANDLER  ( -- )
+Handle the receiving of the RX data using iFLAG and use the low level USB
+ACK/NAK handshake to move data from an endpoint to the RX ring buffer in a controlled way.
+Handle the transmitting of TX data, but only when a connection is made. Before filling
+the TX endpoint check if the previous data packet was sent too.
+Function: USB-KEY?     ( -- flag )
+Leave true flag when there is data in the RX ring buffer, otherwise false
+Call the USB-HANDLER once too
+Function: USB-KEY      ( -- c )
+Leave character 'c' when there is data in the RX ring buffer
+Call the USB-HANDLER waiting for space in the RX ring buffer
+Function: USB-EMIT     ( c -- )
+Store character 'c' when there is space in the TX ring buffer
+Call the USB-HANDLER waiting for space in the TX ring buffer
+Function: USB-ON
+Initialise the USB DPRAM, call START-USB, clear USB-STATE & IFLAG
+finally initialse the KEY?, KEY and EMIT vectors of the used system.
 </code>
-===== Implementation example =====
+===== Generic Forth implementation example =====
 <code forth>
@@ Line 286: / Line 422: @@
 </code>
+===== Implementations =====
+[[https://github.com/WillemOuwerkerk/noForth-T-hardware-examples-RP2040/tree/main/USB-CDC|Different noForth implementations for the USB-CDC driver]]