diff --git a/vm/dv/CPUDEV b/vm/dv/CPUDEV
index 82f5db6..ec0f4eb 100644
--- a/vm/dv/CPUDEV
+++ b/vm/dv/CPUDEV
@@ -8,12 +8,13 @@ CPU device function slots:
     16      -   -   -   -   getmaxidx       rax = maximal index for a register frame
     17      -   -   -   -   getrfusage      rax = number of register frames active
     18      -   -   -   -   getcuridx       rax = index of the current register frame
-    19      i   -   -   -   isactive        rax = is register frame #ax0 active?
-    20      i   -   -   y   activate        activates register frame #ax0
-    21      i   -   -   y   deactivate      deactivates register frame #ax0 (losing all its contents!)
-    22      i   i   -   y   copyframe       copy contents of frame #ax1 into (active) frame #ax0
-    23      i   i   -   y   moveframe       move frame #ax1 to (inactive) frame index #ax0
-   24-31    -   -   -   -   (reserved)      (reserved)
+    19      -   -   -   -   leastavail      rax = least index among inactive frames, -1 if none
+    20      i   -   -   -   isactive        rax = is register frame #ax0 active?
+    21      i   -   -   y   activate        activates register frame #ax0 (filling it with 0's)
+    22      i   -   -   y   deactivate      deactivates register frame #ax0 (losing all its contents!)
+    23      i   i   -   y   copyframe       copy contents of frame #ax1 into (active) frame #ax0
+    24      i   i   -   y   moveframe       move frame #ax1 to (inactive) frame index #ax0
+   25-31    -   -   -   -   (reserved)      (reserved)
     32      i   -   -   -   loadargs        load registers ax0-ax7 from frame #ax0
     33      i   r   -   -   loadreg         rax = register #ax1 from frame #ax0
    34-47    -   -   -   -   (reserved)      (reserved)
diff --git a/vm/dv/cpudev.c b/vm/dv/cpudev.c
index 2a03a27..5cee58f 100644
--- a/vm/dv/cpudev.c
+++ b/vm/dv/cpudev.c
@@ -3,32 +3,114 @@
 
 #include <pc/dev.h>
 
+//----------------------------------------------------------------------------//
+
 #define MAX_RFRAME_IDX 255
 
 //
-// Register frales
+// Register frames
 //
 reg_t **rfs = NULL;
+
+size_t current_idx = 0;
 size_t rfs_used = 0;
 
-long cpudev_testfn(ctx_t *ctx, dev_t *dev)
+#define CHK_INDEX(idx)                                                      \
+    if ((ulong)idx > MAX_RFRAME_IDX)                                        \
+        _except(ctx, E_UDF, "cpudev: invalid rframe index: #%u", idx);
+
+//----------------------------------------------------------------------------//
+
+long cpudev_getmaxidx(ctx_t *ctx, dev_t *dev)
 {
-    rax = 4;
-    rdx = 3;
+    rax = MAX_RFRAME_IDX;
+    return 0;
+}
+
+long cpudev_getrfusage(ctx_t *ctx, dev_t *dev)
+{
+    rax = rfs_used;
+    return 0;
+}
+
+long cpudev_getcuridx(ctx_t *ctx, dev_t *dev)
+{
+    rax = current_idx;
+    return 0;
+}
+
+long cpudev_leastavail(ctx_t *ctx, dev_t *dev)
+{
+    size_t it;
+
+    for (it = 0; it <= MAX_RFRAME_IDX; it++)
+    {
+        if (rfs[it] == NULL)
+        {
+            rax = it;
+            return 0;
+        }
+    }
+
+    rax = -1;
+    return 0;
+}
+
+//----------------------------------------------------------------------------//
+
+long cpudev_isactive(ctx_t *ctx, dev_t *dev)
+{
+    CHK_INDEX(ax0);
+
+    rax = (rfs[ax0] != NULL);
 
     return 0;
 }
 
+long cpudev_activate(ctx_t *ctx, dev_t *dev)
+{
+    CHK_INDEX(ax0);
+    
+    if (rfs[ax0] != NULL)
+        _except(ctx, E_UDF,
+            "cpudev: activating already activated rframe: #%u", ax0);
+
+    return 0;
+}
+
+long cpudev_deactivate(ctx_t *ctx, dev_t *dev)
+{
+    CHK_INDEX(ax0);
+    
+    if (ax0 == 0)
+        _except(ctx, E_UDF, "cpudev: deactivating rframe #0 (arch_r)");
+
+    return 0;
+}
+
+//----------------------------------------------------------------------------//
+
+//----------------------------------------------------------------------------//
+
 long cpudev_poweron(ctx_t *ctx, dev_t *dev)
 {
-    rfs = malloc(sizeof(reg_t *) * (MAX_RFRAME_IDX + 1));
+    rfs = calloc(MAX_RFRAME_IDX + 2, sizeof(reg_t *));
     
     if (rfs == NULL)
         return -1;
 
+    rfs[0] = ctx->r;
+    rfs_used = 1;
+
     dev->state = DEVGOOD;
     
-    dev->fslots[0] = cpudev_testfn;
+    dev->fslots[16] = cpudev_getmaxidx;
+    dev->fslots[17] = cpudev_getrfusage;
+    dev->fslots[18] = cpudev_getcuridx;
+    dev->fslots[19] = cpudev_leastavail;
+    dev->fslots[20] = cpudev_isactive;
+    dev->fslots[21] = cpudev_activate;
+    dev->fslots[22] = cpudev_deactivate;
 
     return 0;
 }
@@ -41,6 +123,8 @@ long cpudev_poweroff(ctx_t *ctx, dev_t *dev)
     return 0;
 }
 
+//----------------------------------------------------------------------------//
+
 dev_t cpudev =
 {
     .type = "cpu",