From b33ccf83ba13ea1370d82f309d318d8817f6db58 Mon Sep 17 00:00:00 2001
From: Astro <astro@spaceboyz.net>
Date: Thu, 18 Jun 2020 18:07:50 +0200
Subject: [PATCH] eth: doc

---
 libboard_zynq/src/eth/rx.rs | 4 ++++
 libboard_zynq/src/eth/tx.rs | 7 ++++---
 2 files changed, 8 insertions(+), 3 deletions(-)

diff --git a/libboard_zynq/src/eth/rx.rs b/libboard_zynq/src/eth/rx.rs
index 2af040d..4efd0ec 100644
--- a/libboard_zynq/src/eth/rx.rs
+++ b/libboard_zynq/src/eth/rx.rs
@@ -81,6 +81,8 @@ impl DescList {
             entry.word1.write(
                 DescWord1::zeroed()
             );
+            // Flush buffer from cache, to be filled by the peripheral
+            // before next read
             dcci_slice(&buffer[..]);
         }
 
@@ -129,6 +131,8 @@ pub struct PktRef<'a> {
 
 impl<'a> Drop for PktRef<'a> {
     fn drop(&mut self) {
+        // Flush buffer from cache, to be filled by the peripheral
+        // before next read
         dcci_slice(self.buffer);
 
         self.entry.word0.modify(|_, w| w.used(false));
diff --git a/libboard_zynq/src/eth/tx.rs b/libboard_zynq/src/eth/tx.rs
index c4acf7d..b326414 100644
--- a/libboard_zynq/src/eth/tx.rs
+++ b/libboard_zynq/src/eth/tx.rs
@@ -124,12 +124,13 @@ pub struct PktRef<'a> {
 
 impl<'a> Drop for PktRef<'a> {
     fn drop(&mut self) {
+        // Write back all dirty cachelines of this buffer
         dcc_slice(self.buffer);
+
         self.entry.word1.modify(|_, w| w.used(false));
         if ! self.regs.tx_status.read().tx_go() {
-            self.regs.net_ctrl.modify(|_, w|
-                                      w.start_tx(true)
-            );
+            // Start TX if not already running
+            self.regs.net_ctrl.modify(|_, w| w.start_tx(true));
         }
     }
 }