feat(eppp): Add support for custom channels

Author: david-cermak

components/eppp_link/Kconfig

@@ -93,4 +93,21 @@ menu "eppp_link"
         default "06:00:00:00:00:02"
         depends on EPPP_LINK_DEVICE_ETH
 
+    config EPPP_LINK_CHANNELS_SUPPORT
+        bool "Enable channel support (multiple logical channels)"
+        default n
+        depends on !EPPP_LINK_DEVICE_ETH
+        help
+            Enable support for multiple logical channels in the EPPP link layer.
+            When enabled, you can configure the number of channels used for communication.
+
+    config EPPP_LINK_NR_OF_CHANNELS
+        int "Number of logical channels"
+        depends on EPPP_LINK_CHANNELS_SUPPORT && !EPPP_LINK_DEVICE_ETH
+        range 1 8
+        default 2
+        help
+            Set the number of logical channels for EPPP link communication.
+            Each channel can be used for independent data streams.
+
 endmenu

components/eppp_link/README.md

@@ -39,6 +39,14 @@ Use `idf.py menuconfig` to select the transport layer:
 
 Use PPP netif for UART; Keep the default (TUN) for others
 
+### Channel support (multiple logical channels)
+
+* `CONFIG_EPPP_LINK_CHANNELS_SUPPORT` -- Enable support for multiple logical channels (default: disabled)
+* `CONFIG_EPPP_LINK_NR_OF_CHANNELS` -- Number of logical channels (default: 2, range: 1-8, only visible if channel support is enabled)
+
+When channel support is enabled, the EPPP link can multiplex multiple logical data streams over the same transport. The number of channels is configurable. Channel support is not available for Ethernet transport.
+
+To use channels in your application, use the `eppp_add_channels()` API and provide your own channel transmit/receive callbacks. These APIs and related types are only available when channel support is enabled in Kconfig.
 
 ## API
 
@@ -57,6 +65,9 @@ Use PPP netif for UART; Keep the default (TUN) for others
 * `eppp_netif_start()` -- Starts the network, could be called after startup or whenever a connection is lost
 * `eppp_netif_stop()` --  Stops the network
 * `eppp_perform()` -- Perform one iteration of the PPP task (need to be called regularly in task-less configuration)
+#ifdef CONFIG_EPPP_LINK_CHANNELS_SUPPORT
+* `eppp_add_channels()` -- Register channel transmit/receive callbacks (only available if channel support is enabled)
+#endif
 
 ## Throughput
 

components/eppp_link/eppp_link.c

@@ -367,3 +367,24 @@ void eppp_close(esp_netif_t *netif)
     eppp_deinit(netif);
     remove_handlers();
 }
+
+#ifdef CONFIG_EPPP_LINK_CHANNELS_SUPPORT
+esp_err_t eppp_add_channels(esp_netif_t *netif, eppp_channel_fn_t *tx, const eppp_channel_fn_t rx, void* context)
+{
+    ESP_RETURN_ON_FALSE(netif != NULL && tx != NULL && rx != NULL, ESP_ERR_INVALID_ARG, TAG, "Invalid arguments");
+    struct eppp_handle *h = esp_netif_get_io_driver(netif);
+    ESP_RETURN_ON_FALSE(h != NULL && h->channel_tx != NULL, ESP_ERR_INVALID_STATE, TAG, "Transport not initialized");
+    *tx = h->channel_tx;
+    h->channel_rx = rx;
+    h->context = context;
+    return ESP_OK;
+}
+
+void* eppp_get_context(esp_netif_t *netif)
+{
+    ESP_RETURN_ON_FALSE(netif != NULL, NULL, TAG, "Invalid netif");
+    struct eppp_handle *h = esp_netif_get_io_driver(netif);
+    ESP_RETURN_ON_FALSE(h != NULL, NULL, TAG, "EPPP Not initialized");
+    return h->context;
+}
+#endif

components/eppp_link/eppp_sdio.c

@@ -13,6 +13,7 @@
 #include "eppp_link.h"
 #include "eppp_transport.h"
 #include "eppp_transport_sdio.h"
+#include "eppp_sdio.h"
 
 #define TAG "eppp_sdio"
 
@@ -67,6 +68,9 @@ eppp_transport_handle_t eppp_sdio_init(struct eppp_config_sdio_s *config)
     ESP_RETURN_ON_FALSE(config, NULL, TAG, "Config cannot be null");
     struct eppp_sdio *h = calloc(1, sizeof(struct eppp_sdio));
     ESP_RETURN_ON_FALSE(h, NULL, TAG, "Failed to allocate eppp_handle");
+#ifdef CONFIG_EPPP_LINK_CHANNELS_SUPPORT
+    h->parent.channel_tx = eppp_sdio_transmit_channel;
+#endif
     h->parent.base.post_attach = post_attach;
     h->is_host = config->is_host;
     esp_err_t (*init_fn)(struct eppp_config_sdio_s * eppp_config) = h->is_host ? eppp_sdio_host_init : eppp_sdio_slave_init;

components/eppp_link/eppp_sdio.h

@@ -1,5 +1,5 @@
 /*
- * SPDX-FileCopyrightText: 2024 Espressif Systems (Shanghai) CO LTD
+ * SPDX-FileCopyrightText: 2024-2025 Espressif Systems (Shanghai) CO LTD
  *
  * SPDX-License-Identifier: Apache-2.0
  */
@@ -8,12 +8,22 @@
 #define MAX_SDIO_PAYLOAD 1500
 #define SDIO_ALIGN(size) (((size) + 3U) & ~(3U))
 #define SDIO_PAYLOAD SDIO_ALIGN(MAX_SDIO_PAYLOAD)
+#define SDIO_PACKET_SIZE SDIO_ALIGN(MAX_SDIO_PAYLOAD + 4)
 #define PPP_SOF 0x7E
 
+
 // Interrupts and registers
 #define SLAVE_INTR      0
 #define SLAVE_REG_REQ   0
 
 // Requests from host to slave
 #define REQ_RESET 1
 #define REQ_INIT  2
+
+struct header {
+    uint8_t magic;
+    uint8_t channel;
+    uint16_t size;
+} __attribute__((packed));
+
+esp_err_t eppp_sdio_transmit_channel(esp_netif_t *netif, int channel, void *buffer, size_t len);

components/eppp_link/eppp_sdio_host.c

@@ -1,5 +1,5 @@
 /*
- * SPDX-FileCopyrightText: 2024 Espressif Systems (Shanghai) CO LTD
+ * SPDX-FileCopyrightText: 2024-2025 Espressif Systems (Shanghai) CO LTD
  *
  * SPDX-License-Identifier: Apache-2.0
  */
@@ -15,6 +15,7 @@
 #include "sdmmc_cmd.h"
 #include "esp_check.h"
 #include "eppp_link.h"
+#include "eppp_transport.h"
 
 #if CONFIG_EPPP_LINK_DEVICE_SDIO_HOST
 
@@ -28,22 +29,27 @@ static SemaphoreHandle_t s_essl_mutex = NULL;
 static essl_handle_t s_essl = NULL;
 static sdmmc_card_t *s_card = NULL;
 
-static DRAM_DMA_ALIGNED_ATTR uint8_t send_buffer[SDIO_PAYLOAD];
-static DMA_ATTR uint8_t rcv_buffer[SDIO_PAYLOAD];
+static DRAM_DMA_ALIGNED_ATTR uint8_t send_buffer[SDIO_PACKET_SIZE];
+static DMA_ATTR uint8_t rcv_buffer[SDIO_PACKET_SIZE];
 
-esp_err_t eppp_sdio_host_tx(void *h, void *buffer, size_t len)
+static esp_err_t eppp_sdio_host_tx_generic(int channel, void *buffer, size_t len)
 {
     if (s_essl == NULL || s_essl_mutex == NULL) {
         // silently skip the Tx if the SDIO not fully initialized
         return ESP_OK;
     }
 
-    memcpy(send_buffer, buffer, len);
-    size_t send_len = SDIO_ALIGN(len);
-    if (send_len > len) {
-        // pad with SOF's
-        memset(&send_buffer[len], PPP_SOF, send_len - len);
-    }
+
+    struct header *head = (void *)send_buffer;
+    head->magic = PPP_SOF;
+    head->channel = channel;
+    head->size = len;
+    memcpy(send_buffer + sizeof(struct header), buffer, len);
+    size_t send_len = SDIO_ALIGN(len + sizeof(struct header));
+//    if (send_len > len) {
+//        // pad with SOF's
+//        memset(&send_buffer[len], PPP_SOF, send_len - len);
+//    }
     xSemaphoreTake(s_essl_mutex, portMAX_DELAY);
     esp_err_t ret = essl_send_packet(s_essl, send_buffer, send_len, PACKET_TIMEOUT_MS);
     if (ret != ESP_OK) {
@@ -56,6 +62,19 @@ esp_err_t eppp_sdio_host_tx(void *h, void *buffer, size_t len)
     return ret;
 }
 
+esp_err_t eppp_sdio_host_tx(void *h, void *buffer, size_t len)
+{
+    return eppp_sdio_host_tx_generic(0, buffer, len);
+}
+
+#ifdef CONFIG_EPPP_LINK_CHANNELS_SUPPORT
+esp_err_t eppp_sdio_transmit_channel(esp_netif_t *netif, int channel, void *buffer, size_t len)
+{
+    return eppp_sdio_host_tx_generic(channel, buffer, len);
+}
+#endif
+
+
 static esp_err_t request_slave_reset(void)
 {
     esp_err_t ret = ESP_OK;
@@ -145,15 +164,37 @@ esp_err_t eppp_sdio_host_rx(esp_netif_t *netif)
     if (intr & ESSL_SDIO_DEF_ESP32.new_packet_intr_mask) {
         esp_err_t ret;
         do {
-            size_t size_read = SDIO_PAYLOAD;
-            ret = essl_get_packet(s_essl, rcv_buffer, SDIO_PAYLOAD, &size_read, PACKET_TIMEOUT_MS);
+            size_t size_read = SDIO_PACKET_SIZE;
+            ret = essl_get_packet(s_essl, rcv_buffer, SDIO_PACKET_SIZE, &size_read, PACKET_TIMEOUT_MS);
             if (ret == ESP_ERR_NOT_FOUND) {
                 ESP_LOGE(TAG, "interrupt but no data can be read");
                 break;
             } else if (ret == ESP_OK) {
                 ESP_LOGD(TAG, "receive data, size: %d", size_read);
+                struct header *head = (void *)rcv_buffer;
+                if (head->magic != PPP_SOF) {
+                    ESP_LOGE(TAG, "invalid magic %x", head->magic);
+                    break;
+                }
+                if (head->channel > NR_OF_CHANNELS) {
+                    ESP_LOGE(TAG, "invalid channel %x", head->channel);
+                    break;
+                }
+                if (head->size > SDIO_PAYLOAD || head->size > size_read) {
+                    ESP_LOGE(TAG, "invalid size %x", head->size);
+                    break;
+                }
                 ESP_LOG_BUFFER_HEXDUMP(TAG, rcv_buffer, size_read, ESP_LOG_VERBOSE);
-                esp_netif_receive(netif, rcv_buffer, size_read, NULL);
+                if (head->channel == 0) {
+                    esp_netif_receive(netif, rcv_buffer + sizeof(struct header), head->size, NULL);
+                } else {
+#if defined(CONFIG_EPPP_LINK_CHANNELS_SUPPORT)
+                    struct eppp_handle *h = esp_netif_get_io_driver(netif);
+                    if (h->channel_rx) {
+                        h->channel_rx(netif, head->channel, rcv_buffer + sizeof(struct header), head->size);
+                    }
+#endif
+                }
                 break;
             } else {
                 ESP_LOGE(TAG, "rx packet error: %08X", ret);

components/eppp_link/eppp_sdio_slave.c

@@ -10,9 +10,9 @@
 #include "esp_netif.h"
 #include "driver/sdio_slave.h"
 #include "eppp_link.h"
+#include "eppp_transport.h"
 #include "eppp_sdio.h"
 #include "esp_check.h"
-
 #if CONFIG_EPPP_LINK_DEVICE_SDIO_SLAVE
 #define BUFFER_NUM 4
 #define BUFFER_SIZE SDIO_PAYLOAD
@@ -21,19 +21,18 @@ static DMA_ATTR uint8_t sdio_slave_rx_buffer[BUFFER_NUM][BUFFER_SIZE];
 static DMA_ATTR uint8_t sdio_slave_tx_buffer[SDIO_PAYLOAD];
 static int s_slave_request = 0;
 
-esp_err_t eppp_sdio_slave_tx(void *h, void *buffer, size_t len)
+static esp_err_t eppp_sdio_host_tx_generic(int channel, void *buffer, size_t len)
 {
     if (s_slave_request != REQ_INIT) {
         // silently skip the Tx if the SDIO not fully initialized
         return ESP_OK;
     }
-    memcpy(sdio_slave_tx_buffer, buffer, len);
-    size_t send_len = SDIO_ALIGN(len);
-    if (send_len > len) {
-        // pad with SOF's if the size is not 4 bytes aligned
-        memset(&sdio_slave_tx_buffer[len], PPP_SOF, send_len - len);
-    }
-
+    struct header *head = (void *)sdio_slave_tx_buffer;
+    head->magic = PPP_SOF;
+    head->channel = channel;
+    head->size = len;
+    memcpy(sdio_slave_tx_buffer + sizeof(struct header), buffer, len);
+    size_t send_len = SDIO_ALIGN(len + sizeof(struct header));
     ESP_LOG_BUFFER_HEXDUMP(TAG, sdio_slave_tx_buffer, send_len, ESP_LOG_VERBOSE);
     esp_err_t ret = sdio_slave_transmit(sdio_slave_tx_buffer, send_len);
     if (ret != ESP_OK) {
@@ -44,6 +43,18 @@ esp_err_t eppp_sdio_slave_tx(void *h, void *buffer, size_t len)
     return ESP_OK;
 }
 
+esp_err_t eppp_sdio_slave_tx(void *h, void *buffer, size_t len)
+{
+    return eppp_sdio_host_tx_generic(0, buffer, len);
+}
+
+#ifdef CONFIG_EPPP_LINK_CHANNELS_SUPPORT
+esp_err_t eppp_sdio_transmit_channel(esp_netif_t *netif, int channel, void *buffer, size_t len)
+{
+    return eppp_sdio_host_tx_generic(channel, buffer, len);
+}
+#endif
+
 static esp_err_t slave_reset(void)
 {
     esp_err_t ret = ESP_OK;
@@ -82,7 +93,29 @@ esp_err_t eppp_sdio_slave_rx(esp_netif_t *netif)
     if (ret == ESP_ERR_NOT_FINISHED || ret == ESP_OK) {
 again:
         ptr = sdio_slave_recv_get_buf(handle, &length);
-        esp_netif_receive(netif, ptr, length, NULL);
+        struct header *head = (void *)ptr;
+        if (head->magic != PPP_SOF) {
+            ESP_LOGE(TAG, "invalid magic %x", head->magic);
+            return ESP_FAIL;
+        }
+        if (head->channel > NR_OF_CHANNELS) {
+            ESP_LOGE(TAG, "invalid channel %x", head->channel);
+            return ESP_FAIL;
+        }
+        if (head->size > SDIO_PAYLOAD || head->size > length) {
+            ESP_LOGE(TAG, "invalid size %x", head->size);
+            return ESP_FAIL;
+        }
+        if (head->channel == 0) {
+            esp_netif_receive(netif, ptr + sizeof(struct header), head->size, NULL);
+        } else {
+#if defined(CONFIG_EPPP_LINK_CHANNELS_SUPPORT)
+            struct eppp_handle *h = esp_netif_get_io_driver(netif);
+            if (h->channel_rx) {
+                h->channel_rx(netif, head->channel, ptr + sizeof(struct header), head->size);
+            }
+#endif
+        }
         if (sdio_slave_recv_load_buf(handle) != ESP_OK) {
             ESP_LOGE(TAG, "Failed to recycle packet buffer");
             return ESP_FAIL;