Add constant for ethernet MTU

Author: dtwood

tm4c129x-hal/src/ethernet.rs

@@ -62,8 +62,10 @@ impl EphyReg {
     }
 }
 
+const ETHERNET_MTU: usize = 1500;
 const NUM_TX_DESCRIPTORS: usize = 2;
 const NUM_RX_DESCRIPTORS: usize = 10;
+
 static RX_DESCRIPTORS: [RDES; NUM_RX_DESCRIPTORS] = [
     RDES::new(),
     RDES::new(),
@@ -78,12 +80,10 @@ static RX_DESCRIPTORS: [RDES; NUM_RX_DESCRIPTORS] = [
 ];
 static TX_DESCRIPTORS: [TDES; NUM_TX_DESCRIPTORS] = [TDES::new(), TDES::new()];
 
-const RX_BUFFER_SIZE: usize = 1536;
-static mut RX_BUFFERS: [[u8; RX_BUFFER_SIZE]; NUM_RX_DESCRIPTORS] =
-    [[0; RX_BUFFER_SIZE]; NUM_RX_DESCRIPTORS];
-const TX_BUFFER_SIZE: usize = RX_BUFFER_SIZE;
-static mut TX_BUFFERS: [[u8; TX_BUFFER_SIZE]; NUM_TX_DESCRIPTORS] =
-    [[0; TX_BUFFER_SIZE]; NUM_TX_DESCRIPTORS];
+static mut RX_BUFFERS: [[u8; ETHERNET_MTU]; NUM_RX_DESCRIPTORS] =
+    [[0; ETHERNET_MTU]; NUM_RX_DESCRIPTORS];
+static mut TX_BUFFERS: [[u8; ETHERNET_MTU]; NUM_TX_DESCRIPTORS] =
+    [[0; ETHERNET_MTU]; NUM_TX_DESCRIPTORS];
 
 fn emac_reset(emac0: &EMAC0) {
     emac0.dmabusmod.modify(|_, w| w.swr().set_bit());
@@ -338,8 +338,7 @@ impl EthernetDevice {
                 RX_DESCRIPTORS[i].rdes0.write(|w| w.own().set_bit());
                 RX_DESCRIPTORS[i].rdes1.write(|w| {
                     w.bits(
-                        DES1_RX_CTRL_CHAINED
-                            | ((RX_BUFFER_SIZE as u32) << DES1_RX_CTRL_BUFF1_SIZE_S),
+                        DES1_RX_CTRL_CHAINED | ((ETHERNET_MTU as u32) << DES1_RX_CTRL_BUFF1_SIZE_S),
                     )
                 });
                 RX_DESCRIPTORS[i]
@@ -428,7 +427,7 @@ impl<'a> Device<'a> for EthernetDevice {
     fn capabilities(&self) -> DeviceCapabilities {
         let mut cap = DeviceCapabilities::default();
 
-        cap.max_transmission_unit = TX_BUFFER_SIZE;
+        cap.max_transmission_unit = ETHERNET_MTU;
         cap.max_burst_size = Some(NUM_TX_DESCRIPTORS);
 
         cap.checksum = ChecksumCapabilities::default();
@@ -471,7 +470,7 @@ impl<'a> phy::RxToken for RxToken<'a> {
 
         let len = ((descriptor.rdes0.read().bits() & DES0_RX_STAT_FRAME_LENGTH_M)
             >> DES0_RX_STAT_FRAME_LENGTH_S) as usize;
-        assert!(len <= RX_BUFFER_SIZE);
+        assert!(len <= ETHERNET_MTU);
         let data =
             unsafe { core::slice::from_raw_parts(descriptor.rdes2.read().bits() as *mut u8, len) };
 
@@ -496,7 +495,7 @@ impl<'a> phy::TxToken for TxToken<'a> {
     {
         let descriptor = *self.descriptor_pointer;
 
-        assert!(len <= TX_BUFFER_SIZE);
+        assert!(len <= ETHERNET_MTU);
 
         let data = unsafe {
             core::slice::from_raw_parts_mut(descriptor.tdes2.read().bits() as *mut u8, len)