Fix max burst size computation

The units are "MTUs," not "bytes." With this in mind, we can burst the
minimum number of buffers.

2 files changed, 4 insertions, 1 deletions

diff --git a/src/bd.rs b/src/bd.rs
index 9d7ac3c..1afb93b 100644
--- a/src/bd.rs
+++ b/src/bd.rs
@@ -153,6 +153,9 @@ impl<'a, D> IoSlices<'a, D> {
     pub(crate) fn mtu(&self) -> usize {
         self.mtu
     }
+    pub(crate) fn len(&self) -> usize {
+        self.ring.len()
+    }
 }
 
 impl<D> IoSlices<'_, D> {
diff --git a/src/lib.rs b/src/lib.rs
index e24ccb7..0eda7f2 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -347,7 +347,7 @@ impl<const N: u8> smoltcp::phy::Device for Enet<N> {
         let mut caps = smoltcp::phy::DeviceCapabilities::default();
         caps.medium = smoltcp::phy::Medium::Ethernet;
         caps.max_transmission_unit = mtu;
-        caps.max_burst_size = Some(mtu);
+        caps.max_burst_size = Some(self.tx_ring.len().min(self.rx_ring.len()));
 
         caps.checksum.ipv4 = smoltcp::phy::Checksum::None;
         caps.checksum.udp = smoltcp::phy::Checksum::None;