From a029f0de5d447e38f8432875a0eb30925c1a333b Mon Sep 17 00:00:00 2001
From: Chloe M <chloe@mensia.org>
Date: Tue, 14 Jul 2026 16:40:06 -0400
Subject: [PATCH] ptos/amd64: ps: Add context switching stub

Signed-off-by: Chloe M <chloe@mensia.org>
---
 service/ptos/arch/amd64/ps/context.c | 16 ++++++++++++++++
 service/ptos/arch/amd64/ps/thread.c  |  7 +++++++
 service/ptos/head/hal/context.h      | 22 ++++++++++++++++++++++
 service/ptos/head/hal/thread.h       |  7 +++++++
 service/ptos/head/ke/sched.h         |  3 +++
 service/ptos/ke/init.c               | 10 ++++++++++
 6 files changed, 65 insertions(+)
 create mode 100644 service/ptos/arch/amd64/ps/context.c
 create mode 100644 service/ptos/head/hal/context.h

diff --git a/service/ptos/arch/amd64/ps/context.c b/service/ptos/arch/amd64/ps/context.c
new file mode 100644
index 0000000..2919d75
--- /dev/null
+++ b/service/ptos/arch/amd64/ps/context.c
@@ -0,0 +1,16 @@
+/*
+ * Copyright (c) 2026, Chloe M.
+ * Provided under the BSD-3 clause.
+ *
+ * Description: MD context management
+ * Author:      Chloe M.
+ */
+
+#include <hal/context.h>
+#include <ex/trace.h>
+
+VOID
+HalContextSwitch(TRAP_FRAME *Frame)
+{
+    TRACE("CONTEXT SWITCHING IS A TODO\n");
+}
diff --git a/service/ptos/arch/amd64/ps/thread.c b/service/ptos/arch/amd64/ps/thread.c
index affb1f1..449aec2 100644
--- a/service/ptos/arch/amd64/ps/thread.c
+++ b/service/ptos/arch/amd64/ps/thread.c
@@ -10,6 +10,7 @@
 #include <hal/page.h>
 #include <ps/thread.h>
 #include <machine/gdt.h>
+#include <machine/lapic.h>
 #include <mm/vm.h>
 #include <string.h>
 
@@ -79,3 +80,9 @@ HalThreadInit(THREAD *Thread, ULONG Flags, UPTR Ip)
     ThreadInitTcb(Thread, Tcb, Ip);
     return STATUS_SUCCESS;
 }
+
+VOID
+HalPrimeThreadTimer(ULONG Usec)
+{
+    MdLapicTimerOneshotUs(Usec);
+}
diff --git a/service/ptos/head/hal/context.h b/service/ptos/head/hal/context.h
new file mode 100644
index 0000000..2f7a56d
--- /dev/null
+++ b/service/ptos/head/hal/context.h
@@ -0,0 +1,22 @@
+/*
+ * Copyright (c) 2026, Chloe M.
+ * Provided under the BSD-3 clause.
+ *
+ * Description: HAL context management
+ * Author:      Chloe M.
+ */
+
+#ifndef _HAL_CONTEXT_H_
+#define _HAL_CONTEXT_H_ 1
+
+#include <machine/frame.h>
+#include <ptdef.h>
+
+/*
+ * Perform a context switch from one thread to another
+ *
+ * @Frame: Current processor context
+ */
+VOID HalContextSwitch(TRAP_FRAME *Frame);
+
+#endif  /* !_HAL_CONTEXT_H_ */
diff --git a/service/ptos/head/hal/thread.h b/service/ptos/head/hal/thread.h
index 3121451..ce90b39 100644
--- a/service/ptos/head/hal/thread.h
+++ b/service/ptos/head/hal/thread.h
@@ -22,4 +22,11 @@
  */
 PT_STATUS HalThreadInit(THREAD *Thread, ULONG Flags, UPTR Ip);
 
+/*
+ * Prime the scheduler timer
+ *
+ * @Usec: Number of microseconds to prime for
+ */
+VOID HalPrimeThreadTimer(ULONG Usec);
+
 #endif  /* !_HAL_THREAD_H_ */
diff --git a/service/ptos/head/ke/sched.h b/service/ptos/head/ke/sched.h
index a9f54f3..176badc 100644
--- a/service/ptos/head/ke/sched.h
+++ b/service/ptos/head/ke/sched.h
@@ -14,6 +14,9 @@
 #include <ptdef.h>
 #include <queue.h>
 
+/* Minimum scheduler quantum in microseconds */
+#define SCHED_MIN_QUANTUM 900
+
 /*
  * Represents a scheduler queue that threads can be pulled
  * from and added to.
diff --git a/service/ptos/ke/init.c b/service/ptos/ke/init.c
index 7b31a0d..43c1b58 100644
--- a/service/ptos/ke/init.c
+++ b/service/ptos/ke/init.c
@@ -9,11 +9,14 @@
 #include <ptdef.h>
 #include <ke/bpal.h>
 #include <ke/bugcheck.h>
+#include <ke/sched.h>
 #include <ex/trace.h>
 #include <ps/process.h>
 #include <mm/pm.h>
 #include <mm/vm.h>
+#include <hal/prim.h>
 #include <hal/serial.h>
+#include <hal/thread.h>
 #include <hal/kpcr.h>
 #include <drivers/bootvid/fbio.h>
 #include <drivers/acpi/acpi.h>
@@ -95,4 +98,11 @@ KiKernelInit(VOID)
 
     /* Initialize the root process */
     InitializeRootProcess();
+
+    /* Prime the scheduler timer */
+    HalPrimeThreadTimer(SCHED_MIN_QUANTUM);
+
+    for (;;) {
+        HalCpuSpinWait();
+    }
 }