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- EKA2 (EPOC Kernel Architecture 2) is the second-generation Symbian platform real-time operating system kernel, which originated in the earlier operating system EPOC. EKA2 began with a proprietary software license. In October 2009, it was released as free and open-source software under an Eclipse Public License. In April 2011, it was reverted to a proprietary license. Like its predecessor, EKA1, it has preemptive multithreading and full memory protection. The main differences are:
* Real-time guarantees: each application programming interface (API) call is fast, but more importantly, time-bound
* Multiple threads inside the kernel, and outside
* Pluggable memory models, allowing better support for later generations of ARM instruction set architecture.
* A nanokernel which provides the most basic OS facilities upon which other personality layers can be built The user interface of EKA2 is almost fully compatible with EKA1. EKA1 was not used after Symbian OS version 8.1, and was superseded in 2005. The main advantage of EKA2 was its ability to run full telephone signalling protocol stacks. Previously, on Symbian phones, these had to run on a separate central processing unit (CPU). Such signalling stacks are very complex and rewriting them to work natively on Symbian OS is typically not an option. EKA2 thus allows personality layers to emulate the basic primitives of other operating systems, thus allowing existing signalling stacks to run largely unchanged. Real-time guarantees are a prerequisite of signalling stacks, and also help with multimedia tasks. However, as with any RTOS, a full analysis of all threads is needed before any real-time guarantees can be offered to anything except the highest-priority thread; because higher priority threads may prevent lower-priority threads from running. Any multimedia task is likely to involve graphics, storage and/or networking activity, all of which are more likely to disrupt the stream than the kernel is. Inside the kernel, EKA1 only allowed one thread (plus a null idle thread). EKA2 allows many threads. This makes it much easier to write device drivers that involve complex finite-state machines, such as those for SD card memory sticks or USB flash drives. Interrupts are handled with an interrupt service routine, which may request an immediate deferred function call (called as soon as the interrupts are processed), or a deferred function call, which is queued to run on a kernel thread. Either may in turn communicate with user-side threads. Power management in EKA2 was largely unchanged from EKA1. The exact scheme varies between phones, but generally the null thread puts the CPU and peripherals to sleep, after having requested a wake-up whenever the next timer is due to expire. EKA2 runs on ARM architecture CPUs and the WINS emulator. Unofficial ports exist for other CPUs. On the emulator, EKA2 provides somewhat better emulation than EKA1, more so for the RProcess APIs which Symbian OS uses to represent processes. In EKA1 they didn't work at all on the emulator, which runs as a single Windows process. Much of the credit for EKA2 goes to a single Symbian kernel engineer, who began the project as an experiment many years before it became an official part of Symbian OS. (en)
- EKA2（Epoc Kernel Architecture）是Symbian OS的第二代核心。 如同它的第一代核心EKA1一般，具有先佔式多工與記憶體保護功能。兩者主要的差異在於：
* 即時處理（real-time）的保證（API的呼叫是快速、更重要、時間限制內）
* 多執行緒的支持
* 隨插式記憶體模型，支持更多的ARM處理器指令
* 更友善的使用者介面支持，讓使用者可以在Symbian OS 8.0以及8.1中選取核心的設定。 EKA2最主要的優勢還在於支持電話具信號堆疊（singalling stacks）。一般而言，Symbian OS的手機通常是執行於分散的處理器，或是同一個處理器，但是必須使用到複雜而且靠不住的“hacks”。這樣的“具信號堆疊”實在過於複雜，想將程式碼改寫，使其能在Symbian OS自然的運作，顯然不容易做到。因此，EKA2提供了客制化層級（personality layers），實現一般作業系統的基礎基元（basic primitives），允許具信號堆疊在Symbian OS上可擁有更多的不變性。 (zh)
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