# tt_tdp_limit_w

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## Name

### Prometheus Metric Name

```
tt_tdp_limit_w
```

### Metric Path (tt-telemetry)

Schema:

```
{hostname}/tray{tray}/chip{chip}/tt_tdp_limit_w
```

Example path:

```
bh-glx-c09u02/tray1/chip2/tt_tdp_limit_w
```

## Description

The Thermal Design Power (TDP) limit in watts that the ARC firmware throttler currently enforces.
When power consumption (`tt_tdp_w`) approaches this limit, firmware throttles the AI clock to keep
the device within it.

This is distinct from `tt_board_power_limit_w`. The board power limit is the static maximum the
board is configured to draw, whereas this metric reports the limit the throttler is actively
enforcing, which can be reprogrammed at runtime. The limit applies per ASIC, is not arbitrated
between callers (the last write wins), and reverts to the board default on chip reset. Firmware
accepts limits in the range 50 W to 500 W, and refuses any limit above the board's configured
maximum.

Because the limit can be lowered out from under a running workload, comparing this metric against
`tt_tdp_w` is the way to tell whether a device is being power-capped below its board maximum.

This metric is only created if the device's firmware reports the TDP limit. It requires Wormhole
firmware 18.4 or newer, or Blackhole firmware 19.8 or newer; older firmware does not publish the
value and no metric is created.

## Values

**Type:** Unsigned Integer

**Units:** Watts (W)

**Allowable values:**
A non-negative integer representing the enforced TDP limit in watts. For example, `300` means
firmware throttles the device to stay within 300 watts. A value of `0` means the board never
configured a TDP limit; the value firmware reports is published as-is, so consumers that treat the
limit as a ceiling should filter out `0`.

## Related Metrics

|Metric|Description|
|---|---|
|[tt_tdp_w](tt_tdp_w.md)|The current power consumption. This is the value that `tt_tdp_limit_w` throttles against.|
|[tt_board_power_limit_w](tt_board_power_limit_w.md)|The board power limit. The static maximum the board is configured to draw, which the enforced TDP limit cannot exceed.|
|[tt_ai_clock_mhz](tt_ai_clock_mhz.md)|The AI clock frequency, which firmware reduces when the TDP limit is reached.|

## Prometheus Labels

|Label Name|Value|
|---|---|
|hostname|The host from which the metric was collected.|
|hall|The datacenter hall where the host is located. Sourced from the Factory System Descriptor (FSD).|
|aisle|The datacenter aisle where the host is located. Sourced from the Factory System Descriptor (FSD).|
|rack|The rack number where the host is located. Sourced from the Factory System Descriptor (FSD).|
|shelf_u|The shelf U position in the rack where the host is located. Sourced from the Factory System Descriptor (FSD).|
|tray|The tray (UBB) that the device is located on.|
|chip|The ASIC location within the tray.|
|unit|The unit of measurement. Always `"W"` for this metric.|