From bbfa20befe163c04d0a99278107f2608639318d3 Mon Sep 17 00:00:00 2001
From: taitep <taitep@taitep.se>
Date: Thu, 29 Jan 2026 19:07:43 +0100
Subject: Replace custom UART with a sifive uart subset

---
 src/devices/serial/fifo.rs | 113 +++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 113 insertions(+)
 create mode 100644 src/devices/serial/fifo.rs

(limited to 'src/devices/serial/fifo.rs')

diff --git a/src/devices/serial/fifo.rs b/src/devices/serial/fifo.rs
new file mode 100644
index 0000000..dbf4659
--- /dev/null
+++ b/src/devices/serial/fifo.rs
@@ -0,0 +1,113 @@
+// Copyright (c) 2026 taitep
+// SPDX-License-Identifier: BSD-2-Clause
+//
+// This file is part of TRVE (https://gitea.taitep.se/taitep/trve)
+// See LICENSE file in the project root for full license text.
+
+use std::io::{self, Read, Write};
+
+pub struct UartFifo<const CAP: usize> {
+    buf: [u8; CAP],
+    head: usize,
+    tail: usize,
+    len: usize,
+}
+
+impl<const CAP: usize> UartFifo<CAP> {
+    pub fn pop_single_byte(&mut self) -> Option<u8> {
+        if self.is_empty() {
+            return None;
+        }
+
+        let value = self.buf[self.tail];
+        self.advance_read(1);
+        Some(value)
+    }
+
+    pub fn push_single_byte(&mut self, value: u8) -> bool {
+        if self.is_full() {
+            return false;
+        }
+
+        self.buf[self.head] = value;
+        self.advance_write(1);
+        true
+    }
+
+    pub fn is_empty(&self) -> bool {
+        self.len == 0
+    }
+
+    pub fn is_full(&self) -> bool {
+        self.len == CAP
+    }
+
+    fn write_slice(&mut self) -> &mut [u8] {
+        if self.is_full() {
+            return &mut [];
+        }
+
+        if self.head >= self.tail {
+            &mut self.buf[self.head..]
+        } else {
+            &mut self.buf[self.head..self.tail]
+        }
+    }
+
+    fn advance_write(&mut self, n: usize) {
+        debug_assert!(n <= CAP - self.len);
+        self.head = (self.head + n) % CAP;
+        self.len += n;
+    }
+
+    fn read_slice(&self) -> &[u8] {
+        if self.is_empty() {
+            return &[];
+        }
+
+        if self.tail < self.head {
+            &self.buf[self.tail..self.head]
+        } else {
+            &self.buf[self.tail..]
+        }
+    }
+
+    fn advance_read(&mut self, n: usize) {
+        debug_assert!(n <= self.len);
+        self.tail = (self.tail + n) % CAP;
+        self.len -= n;
+    }
+
+    pub fn read_from<R: Read>(&mut self, reader: &mut R) -> io::Result<usize> {
+        let slice = self.write_slice();
+        if slice.is_empty() {
+            return Ok(0);
+        }
+
+        let n = reader.read(slice)?;
+        self.advance_write(n);
+        Ok(n)
+    }
+
+    pub fn write_to<W: Write>(&mut self, writer: &mut W) -> io::Result<usize> {
+        let slice = self.read_slice();
+        if slice.is_empty() {
+            return Ok(0);
+        }
+
+        let n = writer.write(slice)?;
+        self.advance_read(n);
+        Ok(n)
+    }
+}
+
+impl<const SIZE: usize> Default for UartFifo<SIZE> {
+    fn default() -> Self {
+        UartFifo {
+            buf: [0; SIZE],
+            head: 0,
+            tail: 0,
+            len: 0,
+        }
+    }
+}
-- 
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