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

# Glossary

Qualcomm<sup>®</sup> Linux kernel documentation uses the following terms and abbreviations. Terms are listed alphabetically.

## **Terms and definitions**

| Term | Definition |
| - | - |
| **aDSP** | Audio digital signal processor |
| **ALSA** | Advanced Linux Sound Architecture |
| **APSS** | Applications processor subsystem |
| **ASMP** | Asymmetric multiprocessing |
| **BSP** | Board Support Package. The collection of kernel configuration, device trees, drivers, and firmware needed to run Linux on a specific hardware platform. |
| **cDSP** | Compute digital signal processor |
| **CFS** | Completely Fair Scheduler. The default Linux process scheduler that distributes CPU time proportionally among runnable tasks. |
| **CID** | Context identifier |
| **CMA** | Contiguous Memory Allocator. A kernel mechanism that reserves a contiguous physical memory region for devices that require physically contiguous DMA buffers. |
| **COFF** | Common object file format |
| **crosvm** | The ChromeOS virtual machine monitor |
| **DDR** | Double data rate |
| **DMA** | Direct memory access |
| **DMA-buf** | DMA Buffer. A kernel framework for sharing memory buffers between multiple devices and subsystems (for example, GPU, camera, DSP) without unnecessary copies. |
| **DMIPS** | Dhrystone million instructions per second |
| **DSI** | Display Serial Interface |
| **DTB** | Device Tree Blob. The compiled binary form of a Device Tree Source file, passed to the kernel at boot to describe the hardware topology of the platform. |
| **DTBO** | DTB overlays |
| **DTS** | Device Tree Source. The human-readable source file (`.dts`) that describes the hardware components and their relationships on a board. |
| **DTSI** | Device Tree Source Include. A shared Device Tree fragment (`.dtsi`) that describes SoC-level hardware and is included by board-level DTS files. |
| **DTSO** | Device tree source overlay |
| **DVFS** | Dynamic Voltage and Frequency Scaling. A power management technique that adjusts CPU, L3 cache, and DDR operating points at runtime to balance performance and power consumption. |
| **EAS** | Energy Aware Scheduling. A Linux scheduler extension that uses the CPU energy model and PELT signals to place tasks on the most energy-efficient CPU core during wake-up. |
| **eDP** | Embedded DisplayPort |
| **EFI** | Extensible firmware interface |
| **EL2** | Exception Level 2. The ARM exception level at which a hypervisor (such as KVM) runs. Device trees with an `el2` suffix are built for configurations where Linux operates as a KVM host. |
| **ELF** | Executable and linking format |
| **EM** | Energy model |
| **ESP** | EFI System Partition. A FAT32 partition that holds the boot manager, kernel image, initramfs, and optionally the DTB on Qualcomm Linux platforms. |
| **FAT** | File allocation table |
| **GCC** | GNU compiler collection |
| **GIC** | Generic interrupt controller |
| **GPIO** | General Purpose Input/Output. A configurable digital pin on an SoC that can be used for input sensing or output signaling, managed by the pinctrl subsystem. |
| **HDMI** | High-Definition Multimedia Interface |
| **HYP** | Hypervisor |
| **I2C** | Interintegrated circuit |
| **Initrd** | Initial RAM disk |
| **IPC** | Interprocess communication |
| **IRQ** | Interrupt request |
| **ISR** | Interrupt service routine |
| **kas** | A build tool for the Yocto Project that manages layer checkouts and build configurations through declarative YAML files. Qualcomm Linux uses kas configurations stored in `meta-qcom/ci/`. |
| **KGDB** | Kernel GNU Debugger. A kernel built-in debugger that allows source-level debugging of the Linux kernel over a serial connection using GDB on the host. |
| **KGSL** | Kernel graphics support layer |
| **KVM** | Kernel-based Virtual Machine. The Linux hypervisor that enables running guest virtual machines on Qualcomm platforms when the host kernel operates at EL2. |
| **L3** | Level 3 cache |
| **LLCC** | Last level cache controller |
| **LPASS** | Low-power audio subsystem |
| **LTS** | Long-Term Support. A kernel release maintained with security and stability patches for an extended period. Qualcomm Linux tracks an LTS kernel (currently v6.18.x). |
| **MPSS** | Modem peripheral subsystem software |
| **MTP** | Mobile test platform |
| **OS** | Operating system |
| **PAS** | Peripheral authentication service |
| **PBL** | Primary Boot Loader. The first-stage firmware executed from ROM on Qualcomm platforms after power-on. It initialises minimal hardware and loads XBL. |
| **PCI** | Peripheral component interconnect |
| **PD** | Protection domain |
| **PE** | Portable executable file format |
| **PELT** | Per Entity Load Tracking. A kernel mechanism that tracks the historical CPU utilisation of individual tasks and control groups, used by EAS and other scheduler features. |
| **PIL** | Peripheral image loader |
| **PSCI** | Power state coordination interface |
| **PWM** | Pulse width modulation |
| **QCAP** | Qualcomm crash analysis portal |
| **QEMU** | Quick emulator |
| **QPST** | Qualcomm Product Support Tool |
| **QXDM** | Qualcomm extensible diagnostic monitor |
| **remoteproc** | Remote Processor. The Linux kernel framework for loading firmware into and managing heterogeneous processors (aDSP, cDSP, modem) present on Qualcomm SoCs. |
| **RPE** | Reset, power, error |
| **RT** | Real-Time. A kernel configuration (`PREEMPT_RT`) that reduces scheduling latency to bounded, deterministic values, suitable for time-critical workloads. |
| **RTOS** | Real-time operating system |
| **SLPI** | Sensor low-power island |
| **SMD** | Shared memory driver |
| **SMP2P** | Shared memory point to point |
| **SoC** | System on Chip. An integrated circuit that combines CPU cores, memory controllers, DSPs, and peripheral interfaces on a single die. Examples: QCS6490, QCS9100, QCS8300. |
| **SPI** | Serial peripheral interface |
| **SSR** | Subsystem restart |
| **SVM** | Secondary virtual machine |
| **TLMM** | Top-level mode multiplexer |
| **TTY** | Teletype |
| **UCLAMP** | Utilization clamping |
| **UEFI** | Unified Extensible Firmware Interface. The firmware standard used on Qualcomm Linux platforms. UEFI loads systemd-boot as the boot manager after XBL completes platform initialisation. |
| **UKI** | Unified Kernel Image. A single EFI binary that bundles the kernel, initramfs, and optionally the DTB, built with `systemd-ukify` and stored on the ESP. |
| **URI** | Uniform resource identifier |
| **VFIO** | Virtual function I/O |
| **VHE** | Virtual host extensions |
| **VM** | Virtual machine |
| **VMM** | Virtual machine monitor |
| **WCNSS** | Wireless connect subsystem |
| **WDOG** | Watchdog service |
| **WLAN** | Wireless local area network |
| **WPSS** | Wireless processor subsystem |
| **XBL** | eXtensible Boot Loader. The second-stage boot loader on Qualcomm platforms. XBL performs DDR initialisation and loads the UEFI firmware image. |