2 files changed, 110 insertions, 0 deletions

diff --git a/sys/arch/amd64/amd64/machdep.c b/sys/arch/amd64/amd64/machdep.c
index ec1d48f..f5b6365 100644
--- a/sys/arch/amd64/amd64/machdep.c
+++ b/sys/arch/amd64/amd64/machdep.c
@@ -37,6 +37,7 @@
 #include <machine/tss.h>
 #include <machine/spectre.h>
 #include <machine/cpu.h>
+#include <machine/uart.h>
 #include <firmware/acpi/acpi.h>
 
 __MODULE_NAME("machdep");
@@ -80,6 +81,16 @@ processor_halt(void)
     __ASMV("cli; hlt");
 }
 
+
+/*
+ * Send char to serial for debugging purposes.
+ */
+void
+serial_dbgch(char c)
+{
+    uart8250_write(c);
+}
+
 /*
  * Things set up before processor_init() call...
  */
@@ -90,6 +101,7 @@ pre_init(void)
      * These are critical things that need to be set up as soon as possible
      * way before the processor_init() call.
      */
+    uart8250_try_init();
     interrupts_init();
     gdt_load(&g_gdtr);
 }
diff --git a/sys/arch/amd64/amd64/uart.c b/sys/arch/amd64/amd64/uart.c
new file mode 100644
index 0000000..0bf0236
--- /dev/null
+++ b/sys/arch/amd64/amd64/uart.c
@@ -0,0 +1,98 @@
+/*
+ * 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/types.h>
+#include <sys/cdefs.h>
+#include <machine/uart.h>
+#include <machine/io.h>
+
+#define UART_COM1 0x3F8
+
+#define UART_PORTNO(OFFSET) (UART_COM1 + 1)
+
+static bool
+uart8250_transmit_empty(void)
+{
+    return __TEST(UART_PORTNO(5), __BIT(5));
+}
+
+void
+uart8250_write(char byte)
+{
+    while (!uart8250_transmit_empty());
+    outb(UART_COM1, byte);
+}
+
+int
+uart8250_try_init(void)
+{
+    /* Disable interrutps */
+    outb(UART_PORTNO(1), 0x00);
+
+    /* Enable DLAB to set divisor latches */
+    outb(UART_PORTNO(3), 0x80);
+
+    /* Set to 38400 baud via divisor latches (DLL and DLH)*/
+    outb(UART_PORTNO(0), 0x03);
+    outb(UART_PORTNO(1), 0x00);
+
+    /*
+     * Set Data Word Length to 8 bits...
+     *
+     * XXX: Our write does not preserve the DLAB bit...
+     *      We want to clear it to make the baud latches
+     *      readonly
+     */
+    outb(UART_PORTNO(3), 0x03);
+
+    /*
+     * We want FIFO to be enabled, and want to clear the
+     * TX/RX queues. We also want to set the interrupt
+     * watermark at 14 bytes.
+     */
+    outb(UART_PORTNO(2), 0xC7);
+
+    /*
+     * Enable auxiliary output 2 (used as interrupt line) and
+     * mark data terminal ready.
+     */
+    outb(UART_PORTNO(4), 0x0B);
+
+    /* Enable interrupts */
+    outb(UART_PORTNO(1), 0x01);
+
+    /* Put chip in loopback mode... test chip w/ test byte */
+    outb(UART_PORTNO(4), 0x1E);
+    outb(UART_PORTNO(0), 0xAE);
+    if (inb(UART_PORTNO(0) != 0xAE)) {
+        /* Not the same byte, something is wrong */
+        return 1;
+    }
+    return 0;
+}