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