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Pr3265 #3266

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@earlephilhower earlephilhower commented Dec 10, 2025

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functionpointer and others added 6 commits December 10, 2025 18:27
@functionpointer
NCM (Network Control Model) is the newest
8e3432f 
of three protocols for Ethernet over USB.

This implementation in arduino-pico
enables an Ethernet connection with a host PC
over USB without any extra hardware.
Other uses of USB like Serial,
Mouse or Keyboard continue to work in parallel.

It has been tested on Windows and Linux.
MacOS should also work.
@functionpointer
Recompile libpico
5aa6573
@earlephilhower
Merge branch 'master' into usb_ncm_new
57f3700
@functionpointer
USB_NCM: Add weak definition to fix build when not using NCM
7aa5371
@earlephilhower
Override static NCM memory allocation
8b20b79 
The NCM buffers are only accessed in a single file and under very
limited circumstances.  Use a SDKOVERRIDE to make a weak ncm_device
with no memory usage, and put the TUSB ncd_device inside the lwip_usb
folder.

For apps which don't use NCM, this saves >6K of RAM.  For apps which use
NCM, there should be no change.
@earlephilhower
Astyle
ae142c9
@earlephilhower earlephilhower mentioned this pull request Dec 10, 2025
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github-advanced-security[bot]
github-advanced-security bot found potential problems Dec 10, 2025
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cores/rp2040/USB.cpp

extern "C" bool tud_network_recv_cb(const uint8_t *src, uint16_t size) __attribute__((weak));
extern "C" bool tud_network_recv_cb(const uint8_t *src, uint16_t size) {
(void) src;

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cores/rp2040/USB.cpp
extern "C" bool tud_network_recv_cb(const uint8_t *src, uint16_t size) __attribute__((weak));
extern "C" bool tud_network_recv_cb(const uint8_t *src, uint16_t size) {
(void) src;
(void) size;

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libraries/lwIP_USB_NCM/src/utility/NCMEthernet.cpp

NCMEthernet::NCMEthernet(int8_t cs, arduino::SPIClass &spi, int8_t intrpin) {
(void) cs;
(void) spi;

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libraries/lwIP_USB_NCM/src/utility/NCMEthernet.cpp
NCMEthernet::NCMEthernet(int8_t cs, arduino::SPIClass &spi, int8_t intrpin) {
(void) cs;
(void) spi;
(void) intrpin;

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libraries/lwIP_USB_NCM/src/utility/NCMEthernet.cpp
}

bool NCMEthernet::begin(const uint8_t* mac_address, netif *net) {
(void) net;

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libraries/lwIP_USB_NCM/src/utility/NCMEthernet.cpp

if (data_len > bufsize) {
// Packet is bigger than buffer - drop the packet
discardFrame(data_len);

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To fix the problem, you should ensure that discardFrame(data_len); meaningfully performs the discard action. There are two potential approaches:

  1. If discardFrame is supposed to have an effect (i.e., drop the frame): Implement its logic so that it actually discards the data and affects program state.
  2. If discardFrame is intentionally a no-op for some target: Explicitly document that the result is deliberately ignored by casting to (void)discardFrame(data_len); to avoid misunderstandings and to silence CodeQL warnings.
  3. If the code is incomplete, and the implementation should be added later: Add a comment, and/or make the function [[maybe_unused]] or mark it as UNIMPLEMENTED.

Best practice for production code:

  • Implement the discardFrame() method to clear any buffers or update state so that the frame is actually discarded, if required.
  • If it is intentionally a no-op (for hardware or platform reasons), cast to void to document that, and add a code comment justifying the design choice.

What to change, specifically:

  • Insert a proper implementation of discardFrame() if you have access to it in the codebase; otherwise, cast to void at the callsite in readFrame.
  • No additional imports are required.
  • Edit only the file and code shown (libraries/lwIP_USB_NCM/src/utility/NCMEthernet.cpp, line 110).
  • Optionally, add a comment above or at the callsite for future maintainers.
Suggested changeset 1
libraries/lwIP_USB_NCM/src/utility/NCMEthernet.cpp

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Autofix patch
Run the following command in your local git repository to apply this patch
cat << 'EOF' | git apply
diff --git a/libraries/lwIP_USB_NCM/src/utility/NCMEthernet.cpp b/libraries/lwIP_USB_NCM/src/utility/NCMEthernet.cpp
--- a/libraries/lwIP_USB_NCM/src/utility/NCMEthernet.cpp
+++ b/libraries/lwIP_USB_NCM/src/utility/NCMEthernet.cpp
@@ -107,7 +107,7 @@
 
   if (data_len > bufsize) {
     // Packet is bigger than buffer - drop the packet
-    discardFrame(data_len);
+    (void)discardFrame(data_len);  // intentionally ignore result; discard packet if too large
     return 0;
   }
 
EOF
@@ -107,7 +107,7 @@

if (data_len > bufsize) {
// Packet is bigger than buffer - drop the packet
discardFrame(data_len);
(void)discardFrame(data_len); // intentionally ignore result; discard packet if too large
return 0;
}

Copilot is powered by AI and may make mistakes. Always verify output.
libraries/lwIP_USB_NCM/src/utility/NCMEthernet.h
uint16_t readFrame(uint8_t* buffer, uint16_t bufsize);

void discardFrame(uint16_t ign) {
(void) ign;

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3 participants

@earlephilhower @functionpointer