diff --git a/kern/include/ec.h b/kern/include/ec.h
index ead1858..3549ff2 100644
--- a/kern/include/ec.h
+++ b/kern/include/ec.h
@@ -30,6 +30,8 @@ class Ec
     private:
         void        (*cont)();
         Exc_regs    regs;
+        Ec *        prev;
+        Ec *        next;
 
         REGPARM (1)
         static void handle_exc (Exc_regs *) asm ("exc_handler");
@@ -45,6 +47,8 @@ class Ec
         ALWAYS_INLINE
         inline Exc_regs *exc_regs() { return &regs; }
 
+        void enqueue();
+
     public:
         static Ec * current;
 
@@ -78,6 +82,12 @@ class Ec
         NORETURN
         static void sys_dump();
 
+        NORETURN
+        static void sys_create_ec();
+
+        NORETURN
+        static void sys_yield();
+
         ALWAYS_INLINE
         static inline void *operator new (size_t) { return Kalloc::allocator.alloc(sizeof (Ec)); }
 
diff --git a/kern/src/ec.cc b/kern/src/ec.cc
index 223ec4b..1f56b26 100644
--- a/kern/src/ec.cc
+++ b/kern/src/ec.cc
@@ -35,6 +35,9 @@ Ec::Ec (void (*f)(), mword mbi) : cont (f)
     regs.es  = SEL_USER_DATA;
     regs.ss  = SEL_USER_DATA;
     regs.efl = 0x200;           // IF = 1
+
+    // created externally, need to enqueue itself
+    enqueue();
 }
 
 // only used by syscall create thread (EC+SC)
@@ -50,6 +53,20 @@ Ec::Ec (mword eip, mword esp)
     regs.esp = esp;
 }
 
+void Ec::enqueue()
+{
+    if (!current) {
+
+        next = prev = this;
+
+    } else {
+
+        next = current;
+        prev = current->prev;
+        next->prev = prev->next = this;
+    }
+}
+
 void Ec::ret_user_sysexit()
 {
     asm volatile ("lea %0, %%esp;"
@@ -137,6 +154,8 @@ void Ec::handle_tss()
 void Ec::syscall_handler (uint8 n)
 {
     if (n == 0)         sys_dump();
+    else if (n == 1)    sys_create_ec();
+    else if (n == 2)    sys_yield();
 
     printf ("syscall %d - unknown\n", n);
 
@@ -152,6 +171,27 @@ void Ec::sys_dump()
     ret_user_sysexit();
 }
 
+void Ec::sys_create_ec()
+{
+    Sys_create_ec * r = static_cast<Sys_create_ec *>(current->sys_regs());
+
+    Ec * ec = new Ec (r->eip(), r->esp());
+    ec->enqueue();
+
+    printf ("EC:%p SYS_CREATE_EC EC:%p (EIP=%#lx ESP=%#lx)\n", current, ec, r->eip(), r->esp());
+
+    ret_user_sysexit();
+}
+
+void Ec::sys_yield()
+{
+    printf ("EC:%p SYS_YIELD to EC:%p\n", current, current->next);
+
+    current->cont = ret_user_sysexit;
+
+    current->next->make_current();
+}
+
 bool Ec::handle_exc_ts (Exc_regs *r)
 {
     if (r->user())
diff --git a/user/src/user.cc b/user/src/user.cc
index 01791a1..0e9a8fb 100644
--- a/user/src/user.cc
+++ b/user/src/user.cc
@@ -1,3 +1,6 @@
+#define NORETURN            __attribute__((noreturn))
+#define EXTERN_C            extern "C"
+
 unsigned syscall3 (unsigned w0, unsigned w1 = 0, unsigned w2 = 0)
 {
     asm volatile (
@@ -9,8 +12,32 @@ unsigned syscall3 (unsigned w0, unsigned w1 = 0, unsigned w2 = 0)
     return w0;
 }
 
-extern "C" void main_func ()
+void sys_create_ec (void (*eip)(), void* esp)
+{
+    syscall3 (1, reinterpret_cast<unsigned>(eip), reinterpret_cast<unsigned>(esp));
+}
+
+void sys_yield()
+{
+    syscall3 (2);
+}
+
+NORETURN
+void thread()
+{
+    while (1) sys_yield();
+}
+
+EXTERN_C NORETURN
+void main_func ()
 {   
+    char stack[512];
+
+    for (int i=1; i<=8; i++) {
+        sys_create_ec (thread, stack + i * 64);
+        sys_yield ();
+    }
+
     while (1) ;
 }