kernel/amd64: Add 8250 UART driver

Signed-off-by: Ian Moffett <ian@osmora.org>

1 files changed, 81 insertions, 0 deletions

diff --git a/sys/arch/amd64/amd64/uart.c b/sys/arch/amd64/amd64/uart.c
new file mode 100644
index 0000000..9c78434
--- /dev/null
+++ b/sys/arch/amd64/amd64/uart.c
@@ -0,0 +1,81 @@
+/*
+ * Copyright (c) 2023-2024 Ian Marco Moffett and the Osmora Team.
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice,
+ *    this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ * 3. Neither the name of Hyra nor the names of its
+ *    contributors may be used to endorse or promote products derived from
+ *    this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
+ * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
+ * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
+ * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+ * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
+ * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+ * POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#include <sys/param.h>
+#include <machine/uart.h>
+#include <machine/pio.h>
+
+#define UART_COM1 0x3F8
+#define UART_REG(OFFSET) (UART_COM1 + OFFSET)
+
+static inline bool
+uart_transmit_empty(void)
+{
+    return ISSET(UART_REG(5), BIT(5));
+}
+
+void
+uart_write(char byte)
+{
+    while (!uart_transmit_empty());
+    outb(UART_COM1, byte);
+}
+
+int
+uart_init(void)
+{
+    /* Disable interrupts */
+    outb(UART_REG(1), 0x00);
+
+    /* Set DLAB to set baud rate */
+    outb(UART_REG(3), 0x80);
+
+    /* Set rate to 57600 baud */
+    outb(UART_REG(0), 0x02);
+    outb(UART_REG(1), 0x00);
+
+    /* Set data word length to 8 bits and clear DLAB */
+    outb(UART_REG(3), 0x03);
+
+    /* Disable FIFOs for now... (TODO: Use them) */
+    outb(UART_REG(2), 0x00);
+
+    /* Test chip with loopback mode */
+    outb(UART_REG(4), 0x10);
+    outb(UART_REG(0), 0xF0);
+    if (inb(UART_REG(0) != 0xF0))
+        return -1;
+
+    /*
+     * Mark the data terminal ready and clear
+     * loopback mode.
+     */
+    outb(UART_REG(4), 0x01);
+    return 0;
+}