From 6498f85de3078ad7c3206c22c690ecb3d0fa71bb Mon Sep 17 00:00:00 2001
From: Ian McIntyre <me@mciantyre.dev>
Date: Thu, 17 Jul 2025 20:50:40 -0400
Subject: Rewrite descriptors with atomics

The memory ordering ensures that operations to normal memory are
synchronized with operations on device memory, at runtime. I've seen
this play out in the transmit path: writes to the transmit buffer's
flags weren't reaching memory by the time the MAC was checking,
resulting in missing packets. Moving the fence works, but it's better to
use atomics.
---
 src/bd/rxbd.rs | 69 +++++++++++++++-------------------------------------------
 1 file changed, 17 insertions(+), 52 deletions(-)

(limited to 'src/bd/rxbd.rs')

diff --git a/src/bd/rxbd.rs b/src/bd/rxbd.rs
index 8523d6e..ae85a57 100644
--- a/src/bd/rxbd.rs
+++ b/src/bd/rxbd.rs
@@ -1,65 +1,30 @@
 //! Enhanced receive buffer descriptor layout and fields.
 
-use ral_registers::{RORegister, RWRegister};
+use core::sync::atomic::{AtomicU16, AtomicU32, Ordering};
 
 #[repr(C)]
 pub struct RxBD {
-    pub data_length: RORegister<u16>,
-    pub flags: RWRegister<u16>,
-    pub data_buffer_pointer: RWRegister<u32>,
-    pub status: RWRegister<u16>,
-    pub control: RWRegister<u16>,
-    pub checksum: RORegister<u16>,
-    pub header: RORegister<u16>,
+    pub data_length: AtomicU16,
+    pub flags: AtomicU16,
+    pub data_buffer_pointer: AtomicU32,
+    pub status: AtomicU16,
+    pub control: AtomicU16,
+    pub checksum: AtomicU16,
+    pub header: AtomicU16,
     _reserved0: [u16; 1],
-    pub last_bdu: RWRegister<u16>,
-    pub timestamp_1588: RORegister<u32>,
+    pub last_bdu: AtomicU16,
+    pub timestamp_1588: AtomicU32,
     _reserved1: [u16; 4],
 }
 
-bdfields!(flags, u16,
-    empty               [ offset = 15, bits = 1, ],
-    ro1                 [ offset = 14, bits = 1, ],
-    wrap                [ offset = 13, bits = 1, ],
-    ro2                 [ offset = 12, bits = 1, ],
-    last                [ offset = 11, bits = 1, ],
+pub const FLAGS_EMPTY: u16 = 1 << 15;
+pub const FLAGS_WRAP: u16 = 1 << 13;
 
-    miss                [ offset =  8, bits = 1, ],
-    broadcast           [ offset =  7, bits = 1, ],
-    multicast           [ offset =  6, bits = 1, ],
-    length_violation    [ offset =  5, bits = 1, ],
-    non_octet_violation [ offset =  4, bits = 1, ],
-
-    crc_error           [ offset =  2, bits = 1, ],
-    overrun             [ offset =  1, bits = 1, ],
-    truncated           [ offset =  0, bits = 1, ],
-);
-
-bdfields!(status, u16,
-    vlan_priority           [ offset = 13, bits = 3, ],
-    ip_checksum_error       [ offset =  5, bits = 1, ],
-    protocol_checksum_error [ offset =  4, bits = 1, ],
-    vlan                    [ offset =  2, bits = 1, ],
-    ipv6                    [ offset =  1, bits = 1, ],
-    frag                    [ offset =  0, bits = 1, ],
-);
-
-bdfields!(control, u16,
-    mac_error               [ offset = 15, bits = 1, ],
-    phy_error               [ offset = 10, bits = 1, ],
-    collision               [ offset =  9, bits = 1, ],
-    unicast                 [ offset =  8, bits = 1, ],
-    interrupt               [ offset =  7, bits = 1, ],
-);
-
-bdfields!(header, u16,
-    length      [ offset = 11, bits = 5, ],
-    protocol    [ offset =  0, bits = 8, ],
-);
-
-bdfields!(last_bdu, u16,
-    last_bdu    [ offset = 15, bits = 1, ],
-);
+impl RxBD {
+    pub(crate) fn is_empty(&self) -> bool {
+        self.flags.load(Ordering::SeqCst) & FLAGS_EMPTY != 0
+    }
+}
 
 #[cfg(test)]
 mod tests {
-- 
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