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@page page_device_pci_irq PCI INTx interrupts
# Legacy INTx (`irq.c` + core)
**INTx** (legacy PCI pin A–D) assignment and masking. MSI/MSI-X: @ref page_device_pci_msi. DT routing: @ref page_device_pci_ofw.
Sources: **`components/drivers/pci/irq.c`**, INTx helpers in **`pci.c`**.
---
## Assignment (`rt_pci_assign_irq`)
During setup, if host provides **`irq_map`**:
1. Read **`PCIR_INTPIN`** from config
2. Optional **`irq_slot`** swizzle on bridges
3. **`irq_map(pdev, slot, pin)`** → **`pdev->irq`**
4. Write **`PCIR_INTLINE`** in config
Without **`irq_map`**, logs debug and leaves IRQ 0 — use OFW or MSI.
### OFW path
**`rt_pci_ofw_irq_parse_and_map`** sets **`pdev->intx_pic`** and IRQ via **`rt_ofw_map_irq`** — preferred on DT platforms (@ref page_device_pci_ofw).
---
## Swizzling
| API | Role |
| --- | --- |
| **`rt_pci_irq_intx(pdev, pin)`** | Swizzle INTPIN across P2P bridges |
| **`rt_pci_irq_slot(pdev, &pin)`** | Slot number for **`interrupt-map`** key |
Used when building **`interrupt-map`** address cells on root bridge.
---
## Mask / unmask
| API | Role |
| --- | --- |
| **`rt_pci_intx(pdev, enable)`** | Enable/disable INTx in command register |
| **`rt_pci_check_and_mask_intx`** | Mask if supported |
| **`rt_pci_check_and_unmask_intx`** | Unmask |
| **`rt_pci_irq_mask` / `rt_pci_irq_unmask`** | Device-level helpers |
**`pdev->broken_intx_masking`**: set when hardware cannot mask INTx reliably.
---
## Unified vector API (`pci.h`, `RT_PCI_MSI`)
**`rt_pci_alloc_vector(pdev, min, max, flags, affinities)`**:
| Flag | Meaning |
| --- | --- |
| **`RT_PCI_IRQ_F_LEGACY`** | Allow INTx |
| **`RT_PCI_IRQ_F_MSI`** | Allow MSI |
| **`RT_PCI_IRQ_F_MSIX`** | Allow MSI-X |
| **`RT_PCI_IRQ_F_AFFINITY`** | CPU affinity |
Picks best available type; **`rt_pci_free_vector`** on teardown.
---
## Pitfalls
| Issue | Mitigation |
| --- | --- |
| MSI + INTx both active | Core often masks INTx when MSI enabled — use one path |
| **`interrupt-map` missing** | **`-RT_EEMPTY`** from OFW — enable MSI or fix DTS |
| Wrong pin after bridge | Use **`rt_pci_irq_intx`**, not raw config pin on child |
| **`irq == 0`** | May mean unassigned — do not register handler |
## See also
- @ref page_device_pci_msi
- @ref page_device_pci_ofw
- @ref page_device_ofw_irq
- @ref page_device_pic
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