proper RX DMA

port/ethernetif.c

@@ -20,6 +20,7 @@
 
 struct ethernetif {
   ETH_DMADESCTypeDef* DMARxDescToGet;
+  ETH_DMADESCTypeDef* DMARxDescToRead;
   ETH_DMADESCTypeDef* DMATxDescToSet;
 };
 
@@ -29,7 +30,6 @@ __attribute__((aligned(4))) uint8_t MACRxBuf[ETH_RXBUFNB * ETH_RX_BUF_SZE];
 __attribute__((aligned(4))) uint8_t MACTxBuf[ETH_TXBUFNB * ETH_TX_BUF_SZE];
 
 static volatile bool g_link_interrupt_flag = false;
-static volatile bool g_packet_received_flag = false;
 static struct ethernetif eth_state;
 
 static void low_level_init(struct netif* netif);
@@ -114,8 +114,9 @@ static void low_level_init(struct netif* netif) {
 
   // init RX descriptors
   ethernetif->DMARxDescToGet = DMARxDscrTab;
+  ethernetif->DMARxDescToRead = DMARxDscrTab;
   for (int i = 0; i < ETH_RXBUFNB; i++) {
-    DMARxDscrTab[i].Status = 0;
+    DMARxDscrTab[i].Status = ETH_DMARxDesc_OWN;
     DMARxDscrTab[i].Buffer1Addr = (uint32_t)&MACRxBuf[i * ETH_RX_BUF_SZE];
     DMARxDscrTab[i].Buffer2NextDescAddr =
         (uint32_t)&DMARxDscrTab[(i + 1) % ETH_RXBUFNB];
@@ -167,55 +168,42 @@ static err_t low_level_output(struct netif* netif, struct pbuf* p) {
 
 static struct pbuf* low_level_input(struct netif* netif) {
   struct ethernetif* ethernetif = netif->state;
+  struct pbuf* p = NULL;
 
-  uint16_t len = ETH10M->ERXLN;
-
-  if (len < MIN_ETH_FRAME_SIZE || len > ETH_MAX_PACKET_SIZE) {
-    LINK_STATS_INC(link.lenerr);
-    ETH10M->ECON1 |= RB_ETH_ECON1_RXEN;
+  // if OWN bit is set, it's still owned by DMA and no packet rdy
+  if (ethernetif->DMARxDescToRead->Status & ETH_DMARxDesc_OWN) {
     return NULL;
   }
 
-  uint8_t* current_rx_buffer_ptr =
-      (uint8_t*)ethernetif->DMARxDescToGet->Buffer1Addr;
+  // packet ready
+  uint32_t len = (ethernetif->DMARxDescToRead->Status & ETH_DMARxDesc_FL) >> 16;
 
-  struct pbuf* p = pbuf_alloc(PBUF_RAW, len, PBUF_POOL);
+  p = pbuf_alloc(PBUF_RAW, len, PBUF_POOL);
   if (p != NULL) {
+    uint8_t* buffer = (uint8_t*)ethernetif->DMARxDescToRead->Buffer1Addr;
     uint32_t offset = 0;
     for (struct pbuf* q = p; q != NULL; q = q->next) {
-      memcpy(q->payload, current_rx_buffer_ptr + offset, q->len);
+      memcpy(q->payload, buffer + offset, q->len);
       offset += q->len;
     }
     LINK_STATS_INC(link.recv);
-    MIB2_STATS_NETIF_ADD(netif, ifinoctets, len);
   } else {
     LINK_STATS_INC(link.memerr);
     LINK_STATS_INC(link.drop);
-    MIB2_STATS_NETIF_INC(netif, ifindiscards);
   }
 
-  // move to next descriptor
-  ethernetif->DMARxDescToGet =
-      (ETH_DMADESCTypeDef*)ethernetif->DMARxDescToGet->Buffer2NextDescAddr;
-  ETH10M->ERXST = (uint32_t)ethernetif->DMARxDescToGet->Buffer1Addr;
-  ETH10M->ECON1 |= RB_ETH_ECON1_RXEN;
+  // give buffer back to DMA
+  ethernetif->DMARxDescToRead->Status = ETH_DMARxDesc_OWN;
+  // advance read pointer to the next descriptor in the ring
+  ethernetif->DMARxDescToRead =
+      (ETH_DMADESCTypeDef*)ethernetif->DMARxDescToRead->Buffer2NextDescAddr;
 
   return p;
 }
 
 void ethernetif_input(struct netif* netif) {
-  if (!g_packet_received_flag) {
-    return;
-  }
-
-  NVIC_DisableIRQ(ETH_IRQn);
-  if (g_packet_received_flag) {
-    g_packet_received_flag = false;
-  }
-  NVIC_EnableIRQ(ETH_IRQn);
-
-  struct pbuf* p = low_level_input(netif);
-  if (p != NULL) {
+  struct pbuf* p;
+  while ((p = low_level_input(netif)) != NULL) {
     if (netif->input(p, netif) != ERR_OK) {
       pbuf_free(p);
     }
@@ -245,10 +233,31 @@ void ethernetif_link_poll(struct netif* netif) {
 void ETH_IRQHandler(void) __attribute__((interrupt)) __attribute__((used));
 void ETH_IRQHandler(void) {
   uint32_t flags = ETH10M->EIR;
+  struct ethernetif* ethernetif = &eth_state;
 
   if (flags & RB_ETH_EIR_RXIF) {
-    g_packet_received_flag = true;
     ETH10M->EIR = RB_ETH_EIR_RXIF;
+
+    // descriptor should be owned by DMA
+    if (ethernetif->DMARxDescToGet->Status & ETH_DMARxDesc_OWN) {
+      ETH_DMADESCTypeDef* next_desc =
+          (ETH_DMADESCTypeDef*)ethernetif->DMARxDescToGet->Buffer2NextDescAddr;
+
+      // if next descriptor OWN bit is 0, ring is full and we must drop
+      if (!(next_desc->Status & ETH_DMARxDesc_OWN)) {
+        LINK_STATS_INC(link.drop);
+      } else {
+        // process and re-arm
+        ethernetif->DMARxDescToGet->Status &= ~ETH_DMARxDesc_OWN;
+        // write packet len into status field for CPU
+        ethernetif->DMARxDescToGet->Status |=
+            (ETH_DMARxDesc_FS | ETH_DMARxDesc_LS | (ETH10M->ERXLN << 16));
+        // advance descripotor ptr
+        ethernetif->DMARxDescToGet = next_desc;
+        // re-arm receiver with new emtpy buf
+        ETH10M->ERXST = (uint32_t)ethernetif->DMARxDescToGet->Buffer1Addr;
+      }
+    }
   }
 
   if (flags & RB_ETH_EIR_TXIF) {