> ## Documentation Index
> Fetch the complete documentation index at: https://docs.thrindex.com/llms.txt
> Use this file to discover all available pages before exploring further.

# E0402 — DelaysNotSupported

> A layer with synaptic delays was found in an artifact compiled for akida-akd1500. AKD1500 has no delay processing hardware.

<Warning>E0402: synaptic delays cannot be mapped to akida-akd1500</Warning>

## What happened

A `.thx` artifact was validated against the `akida-akd1500` backend and one of its layers contains a synaptic delay encoding. The AKD1500 capability descriptor declares `native_delay_max_steps = 0` and `delay_fallback = Reject`, meaning delays are neither supported natively nor emulated.

## Why

AKD1500 is an **Akida 1.0** device. Temporal Neural Processors (TNP) that provide buffered or recurrent delay processing are an Akida 2.0 feature not present on AKD1500. The hardware executes a single feedforward pass per inference call with no per-synapse timing buffers.

There is no mechanism to emulate per-synapse delays in a single-frame feedforward model. Silently dropping delays would produce incorrect output, so the backend rejects the artifact instead.

## How to fix

**Option A — Use the simulator.** The `sim` backend supports delays up to 65535 timesteps natively (`native_delay_max_steps = 65535`, `delay_fallback = Emulate`):

```python theme={null}
thx.compile(model, "model.thx", target="sim")
```

**Option B — Retrain without delays.** Remove the delay encoding from the model before compiling for `akida-akd1500`. This changes the model's temporal behaviour and will require retraining:

```python theme={null}
# Remove delays from Dense layers — only use in_features, out_features, bias
layer = snn.Dense(in_features=512, out_features=256)
```

## Example

```
E0402: layer[0] has synaptic delays but akida-akd1500 declares native_delay_max_steps=0.
Observed: .thx layer 0 has "delays_b64" delay encoding; delay_fallback=Reject per capability descriptor.
Why: AKD1500 is an Akida 1.0 device. Temporal Neural Processors (TNP) that support
     buffered or recurrent delay processing are an Akida 2.0 feature not present on AKD1500.
What to do: Retrain without delays, or target a backend that supports them.
            The 'sim' backend supports delays up to u16::MAX steps.
Docs: https://docs.thrindex.com/errors/E0402
```