# tt_pcie_link_alive

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## Name

### Prometheus Metric Name

```
tt_pcie_link_alive
```

### Metric Path (tt-telemetry)

Schema:

```
{hostname}/tray{tray}/chip{chip}/pcie/tt_pcie_link_alive
```

Example path:

```
bh-glx-c09u02/tray1/chip2/pcie/tt_pcie_link_alive
```

## Description

Indicates whether the chip's PCIe link responds to a host read. Each collection cycle the telemetry
server asks UMD's hang detector to read a BAR register that the chip is guaranteed to never legitimately
hold as `0xFFFFFFFF`. If the read returns `0xFFFFFFFF`, the PCIe link has silently dropped and any
subsequent reads will also return the all-ones fault signature — recovery usually requires a board
reset.

This metric is only created for MMIO-capable chips on Wormhole and Blackhole architectures, since
those are the devices for which UMD provides a PCIe hang detector. Remote chips and other
architectures are skipped (no metric is emitted).

## Values

**Type:** Boolean

**Units:** None

**Allowable values:**
- **True (1)**: The chip responded normally to the PCIe probe read.
- **False (0)**: The chip returned the `0xFFFFFFFF` fault signature; the PCIe link is hung.

## 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.|