kern/amd64: intel: Add i8254 PIT driver

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

1 files changed, 64 insertions, 0 deletions

diff --git a/src/sys/arch/amd64/intel/i8254.c b/src/sys/arch/amd64/intel/i8254.c
new file mode 100644
index 0000000..5930578
--- /dev/null
+++ b/src/sys/arch/amd64/intel/i8254.c
@@ -0,0 +1,64 @@
+/*
+ * Copyright (c) 2025 Ian Marco Moffett and L5 engineers
+ * 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 the project 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/param.h>
+#include <machine/i8254.h>
+#include <machine/pio.h>
+
+uint16_t
+i8254_get_count(void)
+{
+    uint8_t lo, hi;
+
+    outb(I8254_COMMAND, 0x00);
+    lo = inb(0x40);
+    hi = inb(0x40);
+    return COMBINE8(hi, lo);
+}
+
+void
+i8254_set_reload(uint16_t val)
+{
+    outb(I8254_COMMAND, 0x34);
+    outb(0x40, (val & 0xFF));
+    outb(0x40, (val >> 8) & 0xFF);
+}
+
+void
+i8254_set_frequency(uint64_t freq_hz)
+{
+    uint64_t divisor = I8254_DIVIDEND / freq_hz;
+
+    if ((I8254_DIVIDEND % freq_hz) > (freq_hz / 2)) {
+        ++divisor;
+    }
+
+    i8254_set_reload(divisor);
+}