Merge #19365 #19366 #19367

19365: bootloaders: fix bootloader button logic r=benpicco a=dylad

### Contribution description

In lastest master, the `BTN_BOOTLOADER_INVERTED` logic doesn't work as expected.
This PR fixes the underlying logic by replacing the `BTN_BOOTLOADER_INVERTED` macro definition by a runtime function.
In fact the current code:
```
#ifndef BTN_BOOTLOADER_INVERTED
#if (BTN0_MODE == GPIO_IN_PD)
#define BTN_BOOTLOADER_INVERTED false
#else
#define BTN_BOOTLOADER_INVERTED true
#endif
#endif
```
cannot work because both `BTN0_MODE` and `GPIO_IN_PD` are not known by the precompiler as they are enum values defined at cpu level.
Thus, replaces it by a runtime function in our bootloader applications.
I've also add `GPIO_OD_PU` along side `GPIO_IN_PU` and add a new define (which can be override at board level or app level) in case an external pullup is used.

### Testing procedure
Flash the riotboot_dfu bootloader:
`make BOARD=saml21-xpro -C bootloaders/riotboot_dfu flash`
Then, flash any test app:
`PROGRAMMER=dfu-util USEMODULE=usbus_dfu make BOARD=saml21-xpro -C tests/shell riotboot/flash-slot0`

With master, the application will not start.
With this PR, the application will start after flashing.

### Issues/PRs references
Fixes #19364 


19366: nanocoap_sock: don't include token in empty ACK response r=benpicco a=benpicco



19367: cord: bump reference from draft to rfc r=benpicco a=bergzand

### Contribution description

The draft is an RFC, this bumps the "see also" in the docs to the rfc.

### Testing procedure

Check that the correct RFC is linked in the docs.

### Issues/PRs references

None


Co-authored-by: Dylan Laduranty <dylan.laduranty@mesotic.com>
Co-authored-by: Benjamin Valentin <benjamin.valentin@ml-pa.com>
Co-authored-by: Koen Zandberg <koen@bergzand.net>

bootloaders/riotboot_dfu/main.c

@@ -36,9 +36,19 @@
 
 static bool _bootloader_alternative_mode(void)
 {
-#ifdef BTN_BOOTLOADER_PIN
+#if defined (BTN_BOOTLOADER_PIN) && defined (BTN_BOOTLOADER_MODE)
+    bool state;
+
     gpio_init(BTN_BOOTLOADER_PIN, BTN_BOOTLOADER_MODE);
-    return (bool)gpio_read(BTN_BOOTLOADER_PIN) != BTN_BOOTLOADER_INVERTED;
+    state = gpio_read(BTN_BOOTLOADER_PIN);
+    /* If button configures w/ internal or external pullup, then it is an
+       active-low, thus reverts the logic */
+    if (BTN_BOOTLOADER_EXT_PULLUP || BTN_BOOTLOADER_MODE == GPIO_IN_PU ||
+        BTN_BOOTLOADER_MODE == GPIO_OD_PU ) {
+       return !state;
+    } else {
+        return state;
+    }
 #else
     return false;
 #endif

bootloaders/riotboot_tinyusb_dfu/main.c

@@ -36,9 +36,19 @@
 
 static bool _bootloader_alternative_mode(void)
 {
-#ifdef BTN_BOOTLOADER_PIN
+#if defined (BTN_BOOTLOADER_PIN) && defined (BTN_BOOTLOADER_MODE)
+    bool state;
+
     gpio_init(BTN_BOOTLOADER_PIN, BTN_BOOTLOADER_MODE);
-    return (bool)gpio_read(BTN_BOOTLOADER_PIN) != BTN_BOOTLOADER_INVERTED;
+    state = gpio_read(BTN_BOOTLOADER_PIN);
+    /* If button configures w/ internal or external pullup, then it is an
+       active-low, thus reverts the logic */
+    if (BTN_BOOTLOADER_EXT_PULLUP || BTN_BOOTLOADER_MODE == GPIO_IN_PU ||
+        BTN_BOOTLOADER_MODE == GPIO_OD_PU ) {
+       return !state;
+    } else {
+        return state;
+    }
 #else
     return false;
 #endif

sys/include/net/cord/ep.h

@@ -15,7 +15,7 @@
  * allows RIOT nodes to register themselves with resource directories.
  * It implements the standard endpoint functionality as defined in
  * draft-ietf-core-resource-directory-27.
- * @see https://tools.ietf.org/html/draft-ietf-core-resource-directory-27
+ * @see https://datatracker.ietf.org/doc/html/rfc9176
  *
  * # Design Decisions
  * - all operations provided by this module are fully synchronous, meaning that

sys/include/riotboot/bootloader_selection.h

@@ -58,19 +58,12 @@ extern "C" {
 
 /** @brief Interpretation of @ref BTN_BOOTLOADER_PIN.
  *
- * Set to true for active-low buttons (go to DFU if the pin is low), otherwise
- * to false (go to DFU if the pin is high).
- *
- * The default value for all boards is inverted (active-low), except if
- * BTN0_MODE is defined as GPIO_IN_PD. In this case the value is not
- * inverted (high-active).
+ * This value should be set to true if the button has an *external* pull-up and
+ * thus, works as an active-low button.
+ * If the button has an internal pull-up, the default value should remains false
  */
-#ifndef BTN_BOOTLOADER_INVERTED
-#if (BTN0_MODE == GPIO_IN_PD)
-#define BTN_BOOTLOADER_INVERTED false
-#else
-#define BTN_BOOTLOADER_INVERTED true
-#endif
+#ifndef BTN_BOOTLOADER_EXT_PULLUP
+#define BTN_BOOTLOADER_EXT_PULLUP false
 #endif
 
 /** @brief LED pin for bootloader indication

sys/net/application_layer/nanocoap/sock.c

@@ -136,14 +136,13 @@ static int _sock_recv_buf(nanocoap_sock_t *sock, void **data, void **ctx, uint32
 static int _send_ack(nanocoap_sock_t *sock, coap_pkt_t *pkt)
 {
     coap_hdr_t ack;
-    unsigned tkl = coap_get_token_len(pkt);
 
     const iolist_t snip = {
         .iol_base = &ack,
         .iol_len  = sizeof(ack),
     };
 
-    coap_build_hdr(&ack, COAP_TYPE_ACK, coap_get_token(pkt), tkl,
+    coap_build_hdr(&ack, COAP_TYPE_ACK, NULL, 0,
                    COAP_CODE_EMPTY, ntohs(pkt->hdr->id));
 
     return _sock_sendv(sock, &snip);

sys/riotboot/serial.c

@@ -57,8 +57,11 @@ static inline void uart_write_byte(uart_t uart, uint8_t data)
 
 static inline bool _boot_pin(void)
 {
-#ifdef BTN_BOOTLOADER_PIN
-    if (BTN_BOOTLOADER_INVERTED) {
+#if defined (BTN_BOOTLOADER_PIN) && defined(BTN_BOOTLOADER_MODE)
+    /* Reverts the logic if the button has an internal or external pullup and
+       thus, is an active-low button */
+    if (BTN_BOOTLOADER_EXT_PULLUP || BTN_BOOTLOADER_MODE == GPIO_IN_PU ||
+        BTN_BOOTLOADER_MODE == GPIO_OD_PU ) {
         return !gpio_read(BTN_BOOTLOADER_PIN);
     }
     else {