RTEMS Hewlett Packard PA-RISC Applications Supplement
RTEMS supports applications in which the application and the executive execute within a single thirty-two bit address space. Thus RTEMS and the application share a common four gigabyte address space within a single space. The PA-RISC automatically converts every address from a logical to a physical address each time it is used. The PA-RISC uses information provided in the page table to perform this translation. The following protection levels are assumed:
The PA-RISC space registers and associated stack -- including the stack pointer r27 -- must be initialized when the initialize_executive directive is invoked. RTEMS treats the space registers as system resources shared by all tasks and does not modify or context switch them.
This memory model supports a flat 32-bit address space with addresses ranging from 0x00000000 to 0xFFFFFFFF (4 gigabytes). Each address is represented by a 32-bit value and memory is addressable. The address may be used to reference a single byte, half-word (2-bytes), or word (4 bytes).
RTEMS does not require that logical addresses map directly to physical addresses, although it is desirable in many applications to do so. RTEMS does not need any additional information when physical addresses do not map directly to physical addresses. By not requiring that logical addresses map directly to physical addresses, the memory space of an RTEMS space can be separated from that of a ROM monitor. For example, a ROM monitor may load application programs into a separate logical address space from itself.
RTEMS assumes that the space registers contain the selector for the single data segment when a directive is invoked. This assumption is especially important when developing interrupt service routines.
RTEMS Hewlett Packard PA-RISC Applications Supplement
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