diff --git a/linux/thread.c b/linux/thread.c
index 19b6fff..e201209 100644
--- a/linux/thread.c
+++ b/linux/thread.c
@@ -6,13 +6,15 @@
 
 sigjmp_buf trampoline;
 
-
 __attribute__((__stdcall__))
 uint32_t umka_sched_add_thread(appdata_t *app) {
     fprintf(stderr, "umka_new_sys_threads before\n");
     fprintf(stderr, "kos_task_count: %d\n", kos_task_count);
     if (!sigsetjmp(trampoline, 1)) {
         __asm__ __inline__ __volatile__ (
+        "pushfd;"
+        "bts    dword ptr [esp], 21;"
+        "popfd;"
         "mov    esp, eax"
         :
         : "a"(app->saved_esp)
diff --git a/umka.asm b/umka.asm
index 94e142e..531d602 100644
--- a/umka.asm
+++ b/umka.asm
@@ -41,7 +41,18 @@ public kos_acpi_ssdt_size
 public stack_init
 public net_add_device
 
-cli equ nop
+macro cli {
+        pushfd
+        btr     dword[esp], 21
+        popfd
+}
+
+macro sti {
+        pushfd
+        bts     dword[esp], 21
+        popfd
+}
+
 iretd equ retd
 
 lang fix en
@@ -287,8 +298,6 @@ public umka_os
 proc umka_os uses ebx esi edi
         call    kos_init
 
-;        mov     [fdd_motor_status], 0
-
         mov     eax, -1
         mov     edi, thr_slot_map+4
         mov     [edi-4], dword 0xFFFFFFF8
@@ -365,14 +374,6 @@ proc umka_os uses ebx esi edi
         ret
 endp
 
-; in: edx -> APPDATA for OS/IDLE slot
-; in: ebx = stack base
-proc s2etup_os_slot
-
-
-        ret
-endp
-
 extrn pci_read
 proc pci_read_reg uses ebx esi edi
         mov     ecx, eax
diff --git a/umka_os.c b/umka_os.c
index e54b605..38f7db8 100644
--- a/umka_os.c
+++ b/umka_os.c
@@ -1,4 +1,5 @@
 #include <setjmp.h>
+#define __USE_GNU
 #include <signal.h>
 #include <stdio.h>
 #include <sys/time.h>
@@ -7,16 +8,22 @@
 
 struct itimerval timeout = {.it_value = {.tv_sec = 0, .tv_usec = 10000}};
 
+
 void scheduler(int signo, siginfo_t *info, void *context) {
     (void)signo;
     (void)info;
     (void)context;
 //    printf("##### switching from task %u\n", kos_current_task);
+    ucontext_t *ctx = context;
     if (!sigsetjmp(*kos_slot_base[kos_current_task].fpu_state, 1)) {
 //        printf("##### saved\n");
-        kos_current_task += 1;
-        if (kos_current_task == kos_task_count) {
-            kos_current_task = 1;
+        if (ctx->uc_mcontext.__gregs[REG_EFL] & (1 << 21)) {
+            kos_current_task += 1;
+            if (kos_current_task == kos_task_count) {
+                kos_current_task = 1;
+            }
+        } else {
+            printf("########## cli ############\n");
         }
         kos_current_slot = kos_slot_base + kos_current_task;
         printf("##### kos_current_task: %u\n", kos_current_task);