diff --git a/docs/MODEL_REBUILD.md b/docs/MODEL_REBUILD.md
index dffe95adb..e810d3a8b 100644
--- a/docs/MODEL_REBUILD.md
+++ b/docs/MODEL_REBUILD.md
@@ -88,6 +88,12 @@ For a model that cannot run on the device GPU, compile with the USB AMD GPU atta
 ./models --lebowski --gpu
 ```
 
+The ASM2464PD bridge must run the current tinygrad custom firmware from
+https://github.com/tinygrad/asm2464pd-firmware. Its USB product string starts
+with `custom`; the legacy `USB 3.2 PCIe TinyEnclosure` patch is not compatible
+with comma's current external-GPU runtime. Firmware flashing is a separate,
+explicit hardware setup step and StarPilot never performs it automatically.
+
 The dynamic flag (`--lebowski` above) sets the output and manifest model ID;
 when only one source model is staged, its ONNX filename does not need to match
 that ID. Input format and behavior version are inferred. `--external-gpu`
diff --git a/tinygrad_repo/test/unit/test_usb_gpu_firmware.py b/tinygrad_repo/test/unit/test_usb_gpu_firmware.py
new file mode 100644
index 000000000..09353b8bf
--- /dev/null
+++ b/tinygrad_repo/test/unit/test_usb_gpu_firmware.py
@@ -0,0 +1,37 @@
+import pytest
+
+from tinygrad.runtime.support import system
+
+
+class FakeUSB:
+  def __init__(self, product: str, is_custom: bool):
+    self.product, self.is_custom = product, is_custom
+
+
+def patch_usb_dependencies(monkeypatch, usb):
+  calls = []
+  monkeypatch.setattr(system.System, "flock_acquire", lambda _: object())
+  monkeypatch.setattr(system, "USB3", lambda *args, **kwargs: calls.append((args, kwargs)) or usb)
+  return calls
+
+
+def test_usb_gpu_rejects_legacy_bridge_firmware(monkeypatch):
+  calls = patch_usb_dependencies(monkeypatch, FakeUSB("USB 3.2 PCIe TinyEnclosure", False))
+
+  with pytest.raises(RuntimeError, match="unsupported legacy USB GPU firmware"):
+    system.USBPCIDevice("AM", object(), "usb:3-6")
+
+  assert calls[0][1] == {"use_bot": True}
+
+
+def test_usb_gpu_accepts_custom_bridge_firmware(monkeypatch):
+  usb = FakeUSB("custom ASM2464PD", True)
+  calls = patch_usb_dependencies(monkeypatch, usb)
+  controller = object()
+  monkeypatch.setattr(system, "CustomASM24Controller", lambda candidate: controller if candidate is usb else None)
+  monkeypatch.setattr(system.System, "pci_setup_usb_bars", lambda *args, **kwargs: {2: (0, 1)})
+
+  device = system.USBPCIDevice("AM", object(), "usb:3-6")
+
+  assert calls[0][1] == {"use_bot": True}
+  assert device.usb is controller
diff --git a/tinygrad_repo/tinygrad/runtime/support/system.py b/tinygrad_repo/tinygrad/runtime/support/system.py
index bb47c77d5..34031e965 100644
--- a/tinygrad_repo/tinygrad/runtime/support/system.py
+++ b/tinygrad_repo/tinygrad/runtime/support/system.py
@@ -220,9 +220,11 @@ class USBPCIDevice(PCIDevice):
   def __init__(self, devpref:str, dev, pcibus):
     self.pcibus, self.peer_group = pcibus, f"USBPCIDevice_{pcibus}"
     self.lock_fd = System.flock_acquire(f"{devpref.lower()}_{pcibus.lower()}.lock")
-    usb = USB3(dev, 0x81, 0x83, 0x02, 0x04)
+    usb = USB3(dev, 0x81, 0x83, 0x02, 0x04, use_bot=True)
     if DEBUG >= 1: print(f"am {self.pcibus}: product string: {usb.product!r}")
-    self.usb: CustomASM24Controller | ASM24Controller = CustomASM24Controller(usb) if usb.is_custom else ASM24Controller(usb)
+    if not usb.is_custom:
+      raise RuntimeError(f"unsupported legacy USB GPU firmware ({usb.product!r}); flash the current tinygrad ASM2464PD custom firmware")
+    self.usb: CustomASM24Controller = CustomASM24Controller(usb)
     self._bar_info = System.pci_setup_usb_bars(self.usb, gpu_bus=4, mem_base=0x10000000, pref_mem_base=(32 << 30))
     self.sram = BumpAllocator(size=0x80000, wrap=False) # asm24 controller sram
 
diff --git a/tinygrad_repo/tinygrad/runtime/support/usb.py b/tinygrad_repo/tinygrad/runtime/support/usb.py
index 1ff0d936d..54562b7a5 100644
--- a/tinygrad_repo/tinygrad/runtime/support/usb.py
+++ b/tinygrad_repo/tinygrad/runtime/support/usb.py
@@ -5,10 +5,6 @@ from tinygrad.helpers import DEBUG, DEV, to_mv, round_up, OSX, getenv, ceildiv
 from tinygrad.runtime.support.hcq import MMIOInterface
 from tinygrad.runtime.support import c
 
-CUSTOM_ASM24_PRODUCT_PREFIXES = ("custom", "USB 3.2 PCIe TinyEnclosure")
-
-def is_custom_asm24_product(product:str) -> bool: return product.startswith(CUSTOM_ASM24_PRODUCT_PREFIXES)
-
 def alloc_cbuffer(sz:int) -> tuple[ctypes.Array, memoryview]: return (buf:=(ctypes.c_ubyte * sz)()), to_mv(ctypes.addressof(buf), sz)
 def checked(fn, msg=None):
   @functools.wraps(fn)
@@ -67,7 +63,7 @@ class USB3:
     checked(libusb.libusb_get_device_descriptor)(libusb.libusb_get_device(self.handle), ctypes.byref(_desc))
     _ret = checked(libusb.libusb_get_string_descriptor_ascii)(self.handle, _desc.iProduct, _buf, 256)
     self.product = bytes(_buf[:_ret]).decode("ascii", errors="replace")
-    self.is_custom = is_custom_asm24_product(self.product)
+    self.is_custom = self.product.startswith("custom")
     if self.is_custom: self.use_bot = use_bot = True
 
     # Detach kernel driver if needed