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diff --git a/internals.rst b/internals.rst index 5653c2a..5f1b062 100644 --- a/internals.rst +++ b/internals.rst @@ -32,3 +32,32 @@ Bootstrapping 5. Generate initial task tree. 6. Save all dataspaces to disk. +Virtual machine +^^^^^^^^^^^^^^^ + +The EUMEL0 machine is a process virtual machine just like Pascal’s p-code +machine or the Java Virtual Machine (JVM). It isolates tasks from each other +and the system. Running native code is not possible. EUMEL0 is a multi address +machine with no general purpose registers and thus data lives in virtual memory +only. A few internal registers like instruction counter, condition flag for +branching, several segment and status registers and a stack pointer exist. + +The CISC instruction set was specifically designed for the high-level language +ELAN. It includes arithmetic operations for ELAN’s primitive datatypes such as +signed and unsigned integer as well as float (REAL) and operations for +bytestrings (TEXT) and dataspaces. However the machine itself does not enforce +datatypes at runtime. The usual control flow operations are accompanied by +ELAN-specific call and return instructions. Special instructions for terminal +and archive disk I/O, exception-like error handling and inter-process +communication (IPC) are available. + +The 54 primary instructions can be encoded with two bytes. They consist of a +6 bit opcode and one short operand. Whenever the latter is longer than 10 bit a +long encoding using two bytes plus operands is used. This format also encodes +42 secondary/special instructions. + +Read more instruction encoding details in chapter two of [kernel83]_ and the +ELAN package `eumel coder`_. + +.. _eumel coder: src/basic/eumel%20coder%201.8.1.html + |