diff --git a/pkg/urbit/noun/events.c b/pkg/urbit/noun/events.c
index 730801ee17..31fc7c6e40 100644
--- a/pkg/urbit/noun/events.c
+++ b/pkg/urbit/noun/events.c
@@ -775,6 +775,91 @@ _ce_loom_pure_south(c3_w pgs_w)
   u3P.dit_w[bas_w - 1] &= 0xffffffff >> bit_w;
 }
 
+/* _ce_loom_track_north(): [pgs_w] clean, followed by [dif_w] dirty.
+*/
+void
+_ce_loom_track_north(c3_w pgs_w, c3_w dif_w)
+{
+  c3_w blk_w = pgs_w >> 5;
+  c3_w bit_w = pgs_w & 31;
+  c3_w off_w;
+
+  memset((void*)u3P.dit_w, 0, blk_w << 2);
+
+  if ( bit_w ) {
+    c3_w tib_w = 32 - bit_w;
+    c3_w dat_w = u3P.dit_w[blk_w];
+
+    dat_w   &= 0xffffffff << bit_w;
+
+    if ( dif_w <= tib_w ) {
+      dat_w |= ((1 << dif_w) - 1) << bit_w;
+      dif_w  = 0;
+    }
+    else {
+      dat_w |= 0xffffffff << bit_w;
+      dif_w -= tib_w;
+    }
+
+    u3P.dit_w[blk_w] = dat_w;
+    blk_w += 1;
+  }
+
+  off_w = blk_w;
+  blk_w = dif_w >> 5;
+  bit_w = dif_w & 31;
+
+  memset((void*)(u3P.dit_w + off_w), 0xff, blk_w << 2);
+
+  if ( bit_w ) {
+    u3P.dit_w[off_w + blk_w] |= (1 << bit_w) - 1;
+  }
+}
+
+/* _ce_loom_track_south(): [pgs_w] clean, preceded by [dif_w] dirty.
+*/
+void
+_ce_loom_track_south(c3_w pgs_w, c3_w dif_w)
+{
+  c3_w blk_w = pgs_w >> 5;
+  c3_w bit_w = pgs_w & 31;
+  c3_w bas_w = ((u3P.pag_w - pgs_w) + 31) >> 5;
+  c3_w off_w;
+
+  memset((void*)(u3P.dit_w + bas_w), 0, blk_w << 2);
+
+  //  the following index subtractions (bas_w, off) are safe,
+  //  so long as the south segment never includes all pages
+  //
+  if ( bit_w ) {
+    c3_w tib_w = 32 - bit_w;
+    c3_w dat_w = u3P.dit_w[--bas_w];
+
+    dat_w   &= 0xffffffff >> bit_w;
+
+    if ( dif_w <= tib_w ) {
+      dat_w |= ((1 << dif_w) - 1) << (tib_w - dif_w);
+      dif_w  = 0;
+    }
+    else {
+      dat_w |= 0xffffffff >> bit_w;
+      dif_w -= tib_w;
+    }
+
+    u3P.dit_w[bas_w] = dat_w;
+  }
+
+  blk_w = dif_w >> 5;
+  bit_w = dif_w & 31;
+  off_w = bas_w - blk_w;
+
+  memset((void*)(u3P.dit_w + off_w), 0xff, blk_w << 2);
+
+  if ( bit_w ) {
+    u3P.dit_w[off_w - 1] |= ((1 << bit_w) - 1) << (32 - bit_w);
+  }
+}
+
 /* _ce_loom_protect_north(): protect/track pages from the bottom of memory.
 */
 static void
diff --git a/pkg/urbit/tests/events_tests.c b/pkg/urbit/tests/events_tests.c
new file mode 100644
index 0000000000..f8615efcbf
--- /dev/null
+++ b/pkg/urbit/tests/events_tests.c
@@ -0,0 +1,238 @@
+#include "all.h"
+
+/* _setup(): prepare for tests.
+*/
+static void
+_setup(void)
+{
+  //  NB: no loom
+  //
+  u3P.pag_w = u3a_pages;
+}
+
+static c3_w
+_check_north_clean(void)
+{
+  c3_w i_w, pag_w, blk_w, bit_w;
+
+  for ( i_w = 0; i_w < u3P.pag_w; i_w++ ) {
+    pag_w = i_w;
+    blk_w = pag_w >> 5;
+    bit_w = pag_w & 31;
+
+    if ( u3P.dit_w[blk_w] & (1 << bit_w) ) {
+      break;
+    }
+  }
+
+  return i_w;
+}
+
+static c3_w
+_check_north_dirty(c3_w pgs_w, c3_w max_w)
+{
+  c3_w i_w, pag_w, blk_w, bit_w;
+
+  for ( i_w = 0; i_w < max_w; i_w++ ) {
+    pag_w = i_w + pgs_w;
+    blk_w = pag_w >> 5;
+    bit_w = pag_w & 31;
+
+    if ( !(u3P.dit_w[blk_w] & (1 << bit_w)) ) {
+      break;
+    }
+  }
+
+  return i_w;
+}
+
+static c3_w
+_check_south_clean(void)
+{
+  c3_w i_w, pag_w, blk_w, bit_w;
+
+  for ( i_w = 0; i_w < u3P.pag_w; i_w++ ) {
+    pag_w = u3P.pag_w - (i_w + 1);
+    blk_w = pag_w >> 5;
+    bit_w = pag_w & 31;
+
+    if ( u3P.dit_w[blk_w] & (1 << bit_w) ) {
+      break;
+    }
+  }
+
+  return i_w;
+}
+
+static c3_w
+_check_south_dirty(c3_w pgs_w, c3_w max_w)
+{
+  c3_w i_w, pag_w, blk_w, bit_w;
+
+  for ( i_w = 0; i_w < max_w; i_w++ ) {
+    pag_w = u3P.pag_w - (i_w + pgs_w + 1);
+    blk_w = pag_w >> 5;
+    bit_w = pag_w & 31;
+
+    if ( !(u3P.dit_w[blk_w] & (1 << bit_w)) ) {
+      break;
+    }
+  }
+
+  return i_w;
+}
+
+void
+_ce_loom_track_north(c3_w pgs_w, c3_w dif_w);
+void
+_ce_loom_track_south(c3_w pgs_w, c3_w dif_w);
+
+static c3_i
+_test_tracking(void)
+{
+  c3_w ret_w;
+
+  u3e_foul();
+
+  if ( 0 != (ret_w = _check_north_clean()) ) {
+    fprintf(stderr, "test events track north init %u\r\n", ret_w);
+    return 0;
+  }
+
+  if ( 0 != (ret_w = _check_south_clean()) ) {
+    fprintf(stderr, "test events track south init %u\r\n", ret_w);
+    return 0;
+  }
+
+  _ce_loom_track_north(100, 0);
+  _ce_loom_track_south(1, 0);
+
+  if ( 100 != (ret_w = _check_north_clean()) ) {
+    fprintf(stderr, "test events track north clean a %u\r\n", ret_w);
+    return 0;
+  }
+
+  if ( 1 != (ret_w = _check_south_clean()) ) {
+    fprintf(stderr, "test events track south clean a %u\r\n", ret_w);
+    return 0;
+  }
+
+  _ce_loom_track_north(75, 25);
+  _ce_loom_track_south(2, 0);
+
+  if ( 75 != (ret_w = _check_north_clean()) ) {
+    fprintf(stderr, "test events track north clean b %u\r\n", ret_w);
+    return 0;
+  }
+
+  if ( 25 != (ret_w = _check_north_dirty(75, 25)) ) {
+    fprintf(stderr, "test events track north dirty b %u\r\n", ret_w);
+    return 0;
+  }
+
+  if ( 2 != (ret_w = _check_south_clean()) ) {
+    fprintf(stderr, "test events track south clean b %u\r\n", ret_w);
+    return 0;
+  }
+
+  _ce_loom_track_north(55, 20);
+  _ce_loom_track_south(1, 1);
+
+  if ( 55 != (ret_w = _check_north_clean()) ) {
+    fprintf(stderr, "test events track north clean c %u\r\n", ret_w);
+    return 0;
+  }
+
+  if ( 20 != (ret_w = _check_north_dirty(55, 20)) ) {
+    fprintf(stderr, "test events track north dirty c %u\r\n", ret_w);
+    return 0;
+  }
+
+  if ( 1 != (ret_w = _check_south_clean()) ) {
+    fprintf(stderr, "test events track south clean c %u\r\n", ret_w);
+    return 0;
+  }
+
+  if ( 1 != (ret_w = _check_south_dirty(1, 1)) ) {
+    fprintf(stderr, "test events track north dirty c %u\r\n", ret_w);
+    return 0;
+  }
+
+  _ce_loom_track_north(255, 0);
+  _ce_loom_track_south(48, 0);
+
+  if ( 255 != (ret_w = _check_north_clean()) ) {
+    fprintf(stderr, "test events track north clean d %u\r\n", ret_w);
+    return 0;
+  }
+
+  if ( 48 != (ret_w = _check_south_clean()) ) {
+    fprintf(stderr, "test events track south clean d %u\r\n", ret_w);
+    return 0;
+  }
+
+  _ce_loom_track_north(213, 42);
+  _ce_loom_track_south(15, 33);
+
+  if ( 213 != (ret_w = _check_north_clean()) ) {
+    fprintf(stderr, "test events track north clean e %u\r\n", ret_w);
+    return 0;
+  }
+
+  if ( 42 != (ret_w = _check_north_dirty(213, 42)) ) {
+    fprintf(stderr, "test events track north dirty e %u\r\n", ret_w);
+    return 0;
+  }
+
+  if ( 15 != (ret_w = _check_south_clean()) ) {
+    fprintf(stderr, "test events track south clean e %u\r\n", ret_w);
+    return 0;
+  }
+
+  if ( 33 != (ret_w = _check_south_dirty(15, 33)) ) {
+    fprintf(stderr, "test events track north dirty e %u\r\n", ret_w);
+    return 0;
+  }
+
+  _ce_loom_track_north(200, 13);
+  _ce_loom_track_south(10, 5);
+
+  if ( 200 != (ret_w = _check_north_clean()) ) {
+    fprintf(stderr, "test events track north clean f %u\r\n", ret_w);
+    return 0;
+  }
+
+  if ( 13 != (ret_w = _check_north_dirty(200, 13)) ) {
+    fprintf(stderr, "test events track north dirty f %u\r\n", ret_w);
+    return 0;
+  }
+
+  if ( 10 != (ret_w = _check_south_clean()) ) {
+    fprintf(stderr, "test events track south clean f %u\r\n", ret_w);
+    return 0;
+  }
+
+  if ( 5 != (ret_w = _check_south_dirty(10, 5)) ) {
+    fprintf(stderr, "test events track north dirty f %u\r\n", ret_w);
+    return 0;
+  }
+
+  return 1;
+}
+
+/* main(): run all test cases.
+*/
+int
+main(int argc, char* argv[])
+{
+   _setup();
+
+  if ( !_test_tracking() ) {
+    fprintf(stderr, "test_events: tracking: failed\r\n");
+    exit(1);
+  }
+
+  fprintf(stderr, "test_events: ok\n");
+
+  return 0;
+}