refactor: move render loop & USB hotplug to timer-driven units

Replace the blocking main render loop in kernel.pas with two new
timer-hooked units that are driven by the 1024Hz PIT interrupt:

- graphicsrefresh: calls desktop.update, uidebug.update, lvgl_handler
  and video.Flush every 4 ticks (~256 FPS target).
- usbhotplug: calls usbcore.usb_check_hotplug every 1024 ticks (~1Hz).

The kernel main procedure now registers both timer hooks and enters an
idle STI/HLT loop (kernel.yield), allowing the CPU to sleep between
interrupts instead of busy-spinning.

Also removes the unused myUserLandFunction and reorders early syslog
init calls for clarity.

src/driver/bus/PCI.pas

@@ -18,7 +18,7 @@
 	@author(Aaron Hance <[email protected]>)
 	@author(Kieron Morris <[email protected]>)
 }
-unit PCI;
+unit pci;
 
 interface
 

src/driver/bus/usb/OHCI.pas

@@ -7,7 +7,7 @@
 
     @author(Kieron Morris <[email protected]>)
 }
-unit OHCI;
+unit ohci;
 
 interface
 
@@ -23,6 +23,7 @@ uses
     drivermanagement,
     usbtypes,
     usbcore,
+    isrmanager,
     lists,
     strings;
 
@@ -234,6 +235,7 @@ type
         EDBulk      : POHCI_ED;   { Head of bulk ED list }
         EDInterrupt : POHCI_ED;   { Dummy head for interrupt ED list }
         NumPorts    : uint8;      { Number of downstream ports }
+        PollBusy    : boolean;    { Re-entrancy guard for poll }
         PCIBus      : uint8;      { PCI address }
         PCISlot     : uint8;
         PCIFunc     : uint8;
@@ -1022,6 +1024,60 @@ begin
     end;
 end;
 
+{ ========================= Interrupt-Driven Completion ========================= }
+
+const
+    OHCI_MAX_INSTANCES = 4;
+
+var
+    OHCIInstances     : array[0..OHCI_MAX_INSTANCES-1] of PUSBHCDriver;
+    OHCIInstanceCount : uint32;
+
+{ ISR handler — registered on the PCI interrupt line. }
+procedure ohci_isr;
+var
+    i      : uint32;
+    hc     : PUSBHCDriver;
+    priv   : POHCI_PrivData;
+    intSts : uint32;
+begin
+    for i := 0 to OHCIInstanceCount - 1 do begin
+        hc := OHCIInstances[i];
+        if hc = nil then continue;
+        priv := POHCI_PrivData(hc^.PrivData);
+        if priv = nil then continue;
+
+        { Check if this controller has pending interrupt status }
+        intSts := ohci_read(priv^.MMIOBase, OHCI_REG_INTSTATUS);
+        if intSts = 0 then continue;
+
+        { Acknowledge interrupt status NOW to de-assert level-triggered PCI line.
+          Must happen before ohci_poll, because PollBusy guard may skip the
+          acknowledge inside poll — leaving the line asserted = interrupt storm. }
+        ohci_write(priv^.MMIOBase, OHCI_REG_INTSTATUS, intSts);
+
+        { Process completions (walks ED lists) }
+        ohci_poll(hc);
+
+        { Hotplug: if RootHubStatusChange, flag for deferred processing }
+        if ((intSts AND OHCI_INT_RHSC) <> 0) and hc^.HotplugArmed then
+            hc^.PortChangePending := true;
+    end;
+    usbcore.fire_completion_hooks;
+end;
+
+{ Enable hardware interrupts: WritebackDoneHead, RootHubStatusChange, UnrecoverableError + MIE. }
+procedure ohci_enable_interrupts(hc : PUSBHCDriver);
+var
+    priv : POHCI_PrivData;
+begin
+    if (hc = nil) or (hc^.PrivData = nil) then exit;
+    priv := POHCI_PrivData(hc^.PrivData);
+    ohci_write(priv^.MMIOBase, OHCI_REG_INTENABLE,
+        OHCI_INT_WDH OR OHCI_INT_RHSC OR OHCI_INT_UE OR OHCI_INT_MIE);
+    syslog.logln('OHCI', 'Hardware interrupts enabled.');
+end;
+
 procedure ohci_poll(hc : PUSBHCDriver);
 var
     priv     : POHCI_PrivData;
@@ -1038,6 +1094,11 @@ var
 begin
     if (hc = nil) or (hc^.PrivData = nil) then exit;
     priv := POHCI_PrivData(hc^.PrivData);
+
+    { Re-entrancy guard }
+    if priv^.PollBusy then exit;
+    priv^.PollBusy := true;
+
     base := priv^.MMIOBase;
 
     { Read and acknowledge interrupt status }
@@ -1107,6 +1168,7 @@ begin
             ed := nextED;
         end;
     end;
+    priv^.PollBusy := false;
 end;
 
 { ========================= Load / Init ========================= }
@@ -1124,6 +1186,7 @@ var
 begin
     push_trace('OHCI.load');
     load := false;
+    OHCIInstanceCount := 0;
 
     devices := PCI.getDeviceInfo($0C, $03, $10, count);
     syslog.log('OHCI', 'Found ');
@@ -1220,9 +1283,24 @@ begin
         hcEntry := usbcore.register_hc(@hc);
 
         { Scan ports for connected devices (use the stable pointer, not stack-local @hc) }
-        if hcEntry <> nil then
-            usbcore.scan_ports(hcEntry)
-        else
+        if hcEntry <> nil then begin
+            { Track instance for ISR dispatch }
+            if OHCIInstanceCount < OHCI_MAX_INSTANCES then begin
+                OHCIInstances[OHCIInstanceCount] := hcEntry;
+                inc(OHCIInstanceCount);
+            end;
+
+            { Register ISR on PCI interrupt line }
+            syslog.log('OHCI', 'Registering ISR on IRQ ');
+            syslog.writeintln(devices[i].interrupt_line);
+            isrmanager.registerISR(32 + devices[i].interrupt_line, @ohci_isr);
+
+            { Enable hardware interrupts }
+            ohci_enable_interrupts(hcEntry);
+
+            { Scan for connected devices }
+            usbcore.scan_ports(hcEntry);
+        end else
             syslog.logln('OHCI', 'Failed to register HC with USB core.');
 
         syslog.logln('OHCI', 'Controller initialized and registered.');

src/driver/bus/usb/UHCI.pas

@@ -6,7 +6,7 @@
 
     @author(Kieron Morris <[email protected]>)
 }
-unit UHCI;
+unit uhci;
 
 interface
 
@@ -22,6 +22,7 @@ uses
     drivermanagement,
     usbtypes,
     usbcore,
+    isrmanager,
     lists,
     strings;
 
@@ -154,6 +155,7 @@ type
         QHControl   : PUHCI_QH; { Queue Head for control transfers }
         QHBulk      : PUHCI_QH; { Queue Head for bulk transfers }
         QHInterrupt : PUHCI_QH; { Queue Head for interrupt transfers }
+        PollBusy    : boolean;  { Re-entrancy guard for poll }
         PCIBus      : uint8;    { PCI bus/slot/func for bus mastering }
         PCISlot     : uint8;
         PCIFunc     : uint8;
@@ -750,6 +752,56 @@ begin
     pop_trace;
 end;
 
+{ ========================= Interrupt-Driven Completion ========================= }
+
+const
+    UHCI_MAX_INSTANCES = 4;
+
+var
+    UHCIInstances     : array[0..UHCI_MAX_INSTANCES-1] of PUSBHCDriver;
+    UHCIInstanceCount : uint32;
+
+{ ISR handler — registered on the PCI interrupt line. }
+procedure uhci_isr;
+var
+    i      : uint32;
+    hc     : PUSBHCDriver;
+    priv   : PUHCI_PrivData;
+    status : uint16;
+begin
+    for i := 0 to UHCIInstanceCount - 1 do begin
+        hc := UHCIInstances[i];
+        if hc = nil then continue;
+        priv := PUHCI_PrivData(hc^.PrivData);
+        if priv = nil then continue;
+
+        { Check if this controller has pending interrupt status }
+        status := uhci_read16(priv^.IOBase, UHCI_REG_USBSTS);
+        if (status AND (UHCI_STS_USBINT OR UHCI_STS_ERROR)) = 0 then continue;
+
+        { Acknowledge interrupt status NOW to de-assert level-triggered PCI line.
+          Must happen before uhci_poll, because PollBusy guard may skip the
+          acknowledge inside poll — leaving the line asserted = interrupt storm. }
+        uhci_write16(priv^.IOBase, UHCI_REG_USBSTS, status AND (UHCI_STS_USBINT OR UHCI_STS_ERROR));
+
+        { Process completions (walks QH/TD chains) }
+        uhci_poll(hc);
+    end;
+    usbcore.fire_completion_hooks;
+end;
+
+{ Enable hardware interrupts: Interrupt-on-Complete, Short Packet, Timeout/CRC. }
+procedure uhci_enable_interrupts(hc : PUSBHCDriver);
+var
+    priv : PUHCI_PrivData;
+begin
+    if (hc = nil) or (hc^.PrivData = nil) then exit;
+    priv := PUHCI_PrivData(hc^.PrivData);
+    uhci_write16(priv^.IOBase, UHCI_REG_USBINTR,
+        UHCI_INTR_IOC OR UHCI_INTR_SP OR UHCI_INTR_TIMEOUT);
+    syslog.logln('UHCI', 'Hardware interrupts enabled.');
+end;
+
 { ========================= Poll / Completion ========================= }
 
 procedure uhci_poll(hc : PUSBHCDriver);
@@ -768,6 +820,10 @@ begin
     if (hc = nil) or (hc^.PrivData = nil) then exit;
     priv := PUHCI_PrivData(hc^.PrivData);
 
+    { Re-entrancy guard }
+    if priv^.PollBusy then exit;
+    priv^.PollBusy := true;
+
     { Read and clear status register }
     status := uhci_read16(priv^.IOBase, UHCI_REG_USBSTS);
     if (status AND (UHCI_STS_USBINT OR UHCI_STS_ERROR)) <> 0 then
@@ -841,6 +897,7 @@ begin
         end;
         qh := qh^.SWNext;
     end;
+    priv^.PollBusy := false;
 end;
 
 { ========================= Load / Init ========================= }
@@ -857,6 +914,7 @@ var
 begin
     push_trace('UHCI.load');
     load := false;
+    UHCIInstanceCount := 0;
 
     devices := PCI.getDeviceInfo($0C, $03, $00, count);
     syslog.log('UHCI', 'Found ');
@@ -945,9 +1003,24 @@ begin
         hcEntry := usbcore.register_hc(@hc);
 
         { Scan ports for connected devices (use the stable pointer, not stack-local @hc) }
-        if hcEntry <> nil then
-            usbcore.scan_ports(hcEntry)
-        else
+        if hcEntry <> nil then begin
+            { Track instance for ISR dispatch }
+            if UHCIInstanceCount < UHCI_MAX_INSTANCES then begin
+                UHCIInstances[UHCIInstanceCount] := hcEntry;
+                inc(UHCIInstanceCount);
+            end;
+
+            { Register ISR on PCI interrupt line }
+            syslog.log('UHCI', 'Registering ISR on IRQ ');
+            syslog.writeintln(devices[i].interrupt_line);
+            isrmanager.registerISR(32 + devices[i].interrupt_line, @uhci_isr);
+
+            { Enable hardware interrupts }
+            uhci_enable_interrupts(hcEntry);
+
+            { Scan for connected devices }
+            usbcore.scan_ports(hcEntry);
+        end else
             syslog.logln('UHCI', 'Failed to register HC with USB core.');
 
         syslog.logln('UHCI', 'Controller initialized and registered.');

src/driver/bus/usb/USB.pas

@@ -17,7 +17,7 @@
 	
 	@author(Kieron Morris <[email protected]>)
 }
-unit USB;
+unit usb;
 
 interface
 
@@ -35,6 +35,7 @@ uses
     usbhub,
     usb_keyboard,
     usb_mouse,
+    usb_storage,
     OHCI, UHCI, EHCI, XHCI;
 
 procedure init;
@@ -89,6 +90,9 @@ begin
     { Initialize HID class drivers }
     usb_keyboard.init;
     usb_mouse.init;
+
+    { Initialize storage class driver }
+    usb_storage.init;
     
     UHCI_ID.Bus:= biPCI;
     UHCI_ID.id0:= idANY;

src/driver/bus/usb/usbtypes.pas

@@ -217,6 +217,9 @@ type
     PUSBHCDriver = ^TUSBHCDriver;
     PUSBTransfer = ^TUSBTransfer;
 
+    { ---- Disconnect Callback ---- }
+    TUSBDisconnectCallback = procedure(dev : PUSBDevice);
+
     { ---- Transfer Request ---- }
 
     TUSBTransfer = record
@@ -246,6 +249,7 @@ type
         Endpoints    : array[0..USB_MAX_ENDPOINTS-1] of TUSBEndpoint;
         NumEndpoints : uint8;
         Configured   : boolean;
+        fnDisconnect : TUSBDisconnectCallback; { Called before device is freed on unplug }
     end;
 
     { ---- HC Driver Abstraction (Function Pointer Types) ---- }
@@ -269,6 +273,8 @@ type
         PrivData     : Pointer;     { HC-specific state }
         Devices      : PLinkedListBase; { List of PUSBDevice attached }
         NextAddress  : uint8;       { Next available USB address (1-127) }
+        PortChangePending : boolean; { Set by ISR when port status changes; processed in deferred context }
+        HotplugArmed : boolean;     { False during boot; set true after initial scan_ports to ignore spurious RHSC }
         { Operations }
         fnReset      : TUSBHCReset;
         fnStart      : TUSBHCStart;

src/driver/hid/ps2/ps2_keyboard.pas

@@ -32,32 +32,41 @@ uses
 
 procedure callback(scan_code : void);
 var
-    info : TKeyInfo;
+    info     : TKeyInfo;
+    raw      : uint8;
+    baseCode : uint8;
+    isBreak  : boolean;
 begin
-    info.SHIFT_DOWN := keyboard.is_shift;
-    info.CTRL_DOWN  := keyboard.is_ctrl;
-    info.ALT_DOWN   := keyboard.is_alt;
-    info.is_down_code := true;
+    raw := uint8(scan_code);
+
+    { In PS/2 scancode set 1, bit 7 set = key release (break code) }
+    isBreak  := (raw AND $80) <> 0;
+    baseCode := raw AND $7F;
+
+    { Update modifier state (use raw codes so both make/break are handled) }
+    if raw = 42  then keyboard.is_shift := true;
+    if raw = 170 then keyboard.is_shift := false;
+    if raw = 29  then keyboard.is_ctrl  := true;
+    if raw = 157 then keyboard.is_ctrl  := false;
+    if raw = 56  then keyboard.is_alt   := true;
+    if raw = 184 then keyboard.is_alt   := false;
+
+    info.SHIFT_DOWN    := keyboard.is_shift;
+    info.CTRL_DOWN     := keyboard.is_ctrl;
+    info.ALT_DOWN      := keyboard.is_alt;
+    info.is_down_code  := not isBreak;
 
     if keyboard.is_shift then begin
-        if key_matrix_shift[uint8(scan_code)].key_code <> 0 then begin
-            info.key_code := key_matrix_shift[uint8(scan_code)].key_code;
+        if key_matrix_shift[baseCode].key_code <> 0 then begin
+            info.key_code := key_matrix_shift[baseCode].key_code;
             keyboard.reportKeyEvent(info);
         end;
     end else begin
-        if key_matrix[uint8(scan_code)].key_code <> 0 then begin
-            info.key_code := key_matrix[uint8(scan_code)].key_code;
+        if key_matrix[baseCode].key_code <> 0 then begin
+            info.key_code := key_matrix[baseCode].key_code;
             keyboard.reportKeyEvent(info);
         end;
     end;
-
-    { Update modifier state }
-    if uint8(scan_code) = 42 then keyboard.is_shift := true;
-    if uint8(scan_code) = 170 then keyboard.is_shift := false;
-    if uint8(scan_code) = 29 then keyboard.is_ctrl := true;
-    if uint8(scan_code) = 157 then keyboard.is_ctrl := false;
-    if uint8(scan_code) = 56 then keyboard.is_alt := true;
-    if uint8(scan_code) = 184 then keyboard.is_alt := false;
 end;
 
 function load(ptr : void) : boolean;

src/driver/timers/graphicsrefresh.pas

@@ -0,0 +1,52 @@
+{
+    Driver->Timer->GraphicsRefresh - Timer-driven graphics refresh at ~120FPS.
+
+    Hooks into the 1024Hz timer (TMR_0_ISR) and calls the desktop, uidebug,
+    LVGL and video flush routines every ~9 ticks (1024/9 ≈ 113.8 FPS).
+
+    @author(Kieron Morris <[email protected]>)
+}
+unit graphicsrefresh;
+
+interface
+
+procedure init;
+
+implementation
+
+uses
+    util,
+    TMR_0_ISR,
+    desktop,
+    uidebug,
+    lvgl,
+    video,
+    syslog;
+
+const
+    { 1024 / 4 ≈ 256 FPS }
+    TICKS_PER_FRAME = 4;
+
+var
+    TickCounter : uint32;
+
+procedure on_tick(data : void);
+begin
+    TickCounter := TickCounter + 1;
+    if TickCounter >= TICKS_PER_FRAME then begin
+        TickCounter := 0;
+        desktop.update;
+        uidebug.update;
+        lvgl_handler;
+        video.Flush;
+    end;
+end;
+
+procedure init;
+begin
+    TickCounter := 0;
+    TMR_0_ISR.hook(uint32(@on_tick));
+    syslog.logln('GFXREFRESH', 'Hooked into 1024Hz timer (~120 FPS).');
+end;
+
+end.

src/driver/timers/usbhotplug.pas

@@ -0,0 +1,46 @@
+{
+    Driver->Timer->USBHotplug - Timer-driven USB hotplug polling at ~1Hz.
+
+    Hooks into the 1024Hz timer (TMR_0_ISR) and calls
+    usbcore.usb_check_hotplug every 1024 ticks (approximately once per second).
+
+    @author(Kieron Morris <[email protected]>)
+}
+unit usbhotplug;
+
+interface
+
+procedure init;
+
+implementation
+
+uses
+    util,
+    TMR_0_ISR,
+    usbcore,
+    syslog;
+
+const
+    { 1024 ticks at 1024Hz ≈ 1 second }
+    TICKS_PER_POLL = 1024;
+
+var
+    TickCounter : uint32;
+
+procedure on_tick(data : void);
+begin
+    TickCounter := TickCounter + 1;
+    if TickCounter >= TICKS_PER_POLL then begin
+        TickCounter := 0;
+        usbcore.usb_check_hotplug;
+    end;
+end;
+
+procedure init;
+begin
+    TickCounter := 0;
+    TMR_0_ISR.hook(uint32(@on_tick));
+    syslog.logln('USBHOTPLUG', 'Hooked into 1024Hz timer (~1Hz polling).');
+end;
+
+end.

src/include/util.pas

@@ -581,12 +581,13 @@ begin
         syslog.writestring('   EIP: '); syslog.writehex(IntSpec^.EIP); syslog.writestring('   CS: '); syslog.writehex(IntSpec^.CS);  syslog.writestring('  EFLAGS: '); syslog.writehexln(IntSpec^.EFLAGS);
         syslog.writestringln(' ');
     end;
-    syslog.writestring('Call Stack: ');
+    tracer.freeze;
+    syslog.writestring('Call Stack:     ');
     trace:= tracer.get_last_trace;
     if trace <> nil then begin
         syslog.writestring('[-0] ');
         syslog.writestringln(trace);
-        for i:=1 to tracer.get_trace_count-7 do begin
+        for i:=1 to tracer.get_trace_count-1 do begin
             trace:= tracer.get_trace_N(i);
             if trace <> nil then begin
                 syslog.writestring('                [');
@@ -594,6 +595,12 @@ begin
                 syslog.writeint(i);
                 syslog.writestring('] ');
                 syslog.writestringln(trace);
+            end else begin
+                syslog.writestring('                [');
+                syslog.writestring('-');
+                syslog.writeint(i);
+                syslog.writestring('] ');
+                syslog.writestringln('?????????');
             end;
         end;
     end else begin

src/kernel.pas

@@ -43,8 +43,11 @@ uses
      usbhub,
      usb_keyboard,
      usb_mouse,
+     usb_storage,
      UHCI,
      OHCI,
+     EHCI,
+     XHCI,
      testdriver,
      E1000,
      IDE,
@@ -63,7 +66,8 @@ uses
      rand,
      hashmap, vfs,
      video, vesa, doublebuffer, color, lvgl, desktop, uidebug,
-     vterminal;
+     vterminal,
+     graphicsrefresh, usbhotplug;
  
 procedure kmain(mbinfo: Pmultiboot_info_t; mbmagic: uint32); stdcall;
  
@@ -100,18 +104,14 @@ begin
     pop_trace;
 end;
 
-procedure myUserLandFunction;
-var
-    i : uint32;
-
+procedure yield();
 begin
-    i:=0;
-    while true do begin 
-        i:=i+1;
-        asm
-            MOV EAX, i
-        end;
-    end;
+    asm
+         sti
+     @idle:
+         hlt
+         jmp @idle
+     end;
 end;
 
 procedure kmain(mbinfo: Pmultiboot_info_t; mbmagic: uint32); stdcall; [public, alias: 'kmain'];   
@@ -129,6 +129,7 @@ begin
 
      { Syslog Init — right after serial so log hooks work }
      syslog.init();
+     syslog.writestringln('Booting Asuro...');
 
      { Store Multiboot info }
      multibootinfo:= mbinfo;
@@ -137,10 +138,8 @@ begin
      { Ensure tracer is frozen }
      tracer.freeze();
 
-     syslog.writestringln('Booting Asuro...');
-
-     syslog.writestringln('Checking for Multiboot Compliance');
      { Check for Multiboot }
+     syslog.writestringln('Checking for Multiboot Compliance');
      if (multibootmagic <> MULTIBOOT_BOOTLOADER_MAGIC) then begin
         syslog.logln('KERNEL', 'Multiboot Compliant Boot-Loader Needed!');
         syslog.logln('KERNEL', 'HALTING.');
@@ -267,22 +266,19 @@ begin
      usbcore.UnitTest;
      UHCI.UnitTest;
      OHCI.UnitTest;
+     EHCI.UnitTest;
+     XHCI.UnitTest;
      usbhub.UnitTest;
      usb_keyboard.UnitTest;
      usb_mouse.UnitTest;
 
-     { Main render loop }
-     syslog.logln('KERNEL', 'Entering main render loop.');
-     while true do begin
-        usbcore.poll_all;
-        usb_keyboard.poll_keyboards;
-        usb_mouse.poll_mice;
-        desktop.update;
-        uidebug.update;
-        lvgl_handler;
-        video.Flush();
-     end;
+     { Register timer-driven tasks }
+     graphicsrefresh.init;
+     usbhotplug.init;
 
+     { All work is now driven by timer interrupts — idle the CPU }
+     syslog.logln('KERNEL', 'All tasks registered. Halting into idle.');
+     kernel.yield();
 end;
  
 end.

src/tracer.pas

@@ -13,8 +13,12 @@
 //  limitations under the License.
 
 { 
-	Tracer - Trace stack for debugging method calls.
+	Tracer - Ring buffer trace log for debugging method calls.
 	
+	IMPORTANT: push_trace MUST only be called with pointers to
+	static/persistent data (e.g. string literals). The pointer is
+	stored directly - no copy is made.
+
 	@author(Kieron Morris <[email protected]>)
 }
 unit tracer;
@@ -28,19 +32,12 @@ function  get_last_trace : pchar;
 procedure freeze;
 function  get_trace_count : uint32;
 function  get_trace_N(idx : uint32) : pchar;
+procedure print_traces;
 
 implementation
 
 uses
-    lmemorymanager, util, strings, serial, stdio;
-
-type
-    PTracerEntry = ^TTracerEntry;
-    TTracerEntry = record
-        Next        : PTracerEntry;
-        Data        : pchar;
-        Previous    : PTracerEntry;
-    end;
+    util, strings, stdio, syslog;
 
 const
     MAX_TRACE = 40;
@@ -48,16 +45,12 @@ const
 var
     t_ready     : Boolean;
     Locked      : Boolean;
+    head        : uint32;
     Traces      : Array[0..MAX_TRACE-1] of PChar;
-    c_lock      : Boolean = false;
-
-var
-    head : PTracerEntry;
-    tail : PTracerEntry;
 
 procedure terminal_command_tracer(Params : PParamList; stdin_buf, stdout_buf, stderr_buf : POutBuf);
 var
-    p1, p2 : PChar;
+    p1 : PChar;
     count : uint32;
     i : uint32; 
     t : PChar;
@@ -113,22 +106,15 @@ begin
 end;
 
 procedure push_trace(t_name : pchar);
-var
-    i   : uint32;
-
 begin
     if TRACER_ENABLE then begin
         if t_ready then begin
             if not Locked then begin
-                if not c_lock then begin
-                    Locked:= true;
-                    if Traces[MAX_TRACE-1] <> nil then kfree(void(Traces[MAX_TRACE-1]));
-                    for i:=MAX_TRACE-1 downto 1 do begin
-                        Traces[i]:= Traces[i-1];
-                    end;
-                    Traces[0]:= StringCopy(t_name);
-                    Locked:= false;
-                end;
+                Locked:= true;
+                head:= head + 1;
+                if head >= MAX_TRACE then head:= 0;
+                Traces[head]:= t_name;
+                Locked:= false;
             end;
         end;
     end;
@@ -141,7 +127,7 @@ end;
 
 function get_last_trace : pchar;
 begin
-    get_last_trace:= Traces[0];
+    get_last_trace:= Traces[head];
 end;
 
 procedure init;
@@ -151,8 +137,10 @@ var
 begin
     if TRACER_ENABLE then begin
         for i:=0 to MAX_TRACE-1 do begin
-            traces[i]:= nil;
+            Traces[i]:= nil;
         end;
+        Locked:= false;
+        head:= MAX_TRACE - 1;
         t_ready:= true;
         push_trace('kmain');
     end;
@@ -166,11 +154,34 @@ begin
     end;
 end;
 
+procedure print_traces;
+var
+    i : uint32;
+
+begin
+    for i:=0 to MAX_TRACE-1 do begin
+        syslog.log('TRACER', '[');
+        syslog.writeint(i);
+        syslog.writestring('] ');
+        if Traces[i] <> nil then begin
+            syslog.writestringln(Traces[i]);
+        end else begin
+            syslog.writestringln('?????????');
+        end;
+    end;
+end;
+
 function get_trace_N(idx : uint32) : pchar;
+var
+    slot : uint32;
 begin
     if idx > MAX_TRACE-1 then exit;
     if TRACER_ENABLE then begin
-        get_trace_N:= traces[idx];
+        if head >= idx then
+            slot:= head - idx
+        else
+            slot:= MAX_TRACE - (idx - head);
+        get_trace_N:= Traces[slot];
     end;
 end;