From 62aa3d103fef1d2c7c9bffe689ddde89420cad7a Mon Sep 17 00:00:00 2001
From: Marian Buschsieweke <marian.buschsieweke@ovgu.de>
Date: Wed, 29 Jul 2020 11:02:59 +0200
Subject: [PATCH] cpu/stm32/periph_eth: RX Timestamps

---
 cpu/stm32/periph/eth.c | 44 ++++++++++++++++++++++++++----------------
 1 file changed, 27 insertions(+), 17 deletions(-)

diff --git a/cpu/stm32/periph/eth.c b/cpu/stm32/periph/eth.c
index 8b51995d43..fc83f3454b 100644
--- a/cpu/stm32/periph/eth.c
+++ b/cpu/stm32/periph/eth.c
@@ -32,6 +32,7 @@
 #include "net/eui_provider.h"
 #include "net/netdev/eth.h"
 #include "periph/gpio.h"
+#include "timex.h"
 
 #define ENABLE_DEBUG            0
 #define ENABLE_DEBUG_VERBOSE    0
@@ -618,12 +619,12 @@ static void handle_lost_rx_irqs(void)
     }
 }
 
-static int stm32_eth_recv(netdev_t *netdev, void *buf, size_t max_len,
-                          void *info)
+static int stm32_eth_recv(netdev_t *netdev, void *_buf, size_t max_len,
+                          void *_info)
 {
-    (void)info;
     (void)netdev;
-    char *data = buf;
+    netdev_eth_rx_info_t *info = _info;
+    char *buf = _buf;
     /* Determine the size of received frame. The frame might span multiple
      * DMA buffers */
     int size = get_rx_frame_size();
@@ -650,20 +651,29 @@ static int stm32_eth_recv(netdev_t *netdev, void *buf, size_t max_len,
         return -ENOBUFS;
     }
 
+    /* Fetch payload, collect RX timestamp from last descriptor if module periph_ptp is used, and
+     * hand DMA descriptors back to the DMA */
     size_t remain = size;
-    while (remain) {
-        size_t chunk = MIN(remain, ETH_RX_BUFFER_SIZE);
-        memcpy(data, rx_curr->buffer_addr, chunk);
-        data += chunk;
-        remain -= chunk;
-        /* Hand over descriptor to DMA */
-        rx_curr->status = RX_DESC_STAT_OWN;
-        rx_curr = rx_curr->desc_next;
-    }
-
-    if ((size + ETHERNET_FCS_LEN - 1) % ETH_RX_BUFFER_SIZE < ETHERNET_FCS_LEN) {
-        /* one additional rx descriptor was needed only for the FCS, hand that
-         * back to the DMA as well */
+    while (1) {
+        /* there can be one more DMA descriptor than needed for holding the Ethernet
+         * payload, as the 4 byte FCS will also be stored by DMA */
+        if (remain) {
+            size_t chunk = MIN(remain, ETH_RX_BUFFER_SIZE);
+            memcpy(buf, rx_curr->buffer_addr, chunk);
+            buf += chunk;
+            remain -= chunk;
+        }
+        if (rx_curr->status & RX_DESC_STAT_LS) {
+            /* LS bit set --> reached last DMA descriptor of this frame */
+            if (IS_USED(MODULE_PERIPH_PTP)) {
+                info->timestamp = rx_curr->ts_low;
+                info->timestamp += (uint64_t)rx_curr->ts_high * NS_PER_SEC;
+                info->flags |= NETDEV_ETH_RX_INFO_FLAG_TIMESTAMP;
+            }
+            rx_curr->status = RX_DESC_STAT_OWN;
+            rx_curr = rx_curr->desc_next;
+            break;
+        }
         rx_curr->status = RX_DESC_STAT_OWN;
         rx_curr = rx_curr->desc_next;
     }