diff options
Diffstat (limited to 'c-user/partition/background.rst')
| -rw-r--r-- | c-user/partition/background.rst | 50 |
1 files changed, 50 insertions, 0 deletions
diff --git a/c-user/partition/background.rst b/c-user/partition/background.rst new file mode 100644 index 0000000..ce38fc7 --- /dev/null +++ b/c-user/partition/background.rst @@ -0,0 +1,50 @@ +.. SPDX-License-Identifier: CC-BY-SA-4.0 + +.. Copyright (C) 1988, 2008 On-Line Applications Research Corporation (OAR) + +Background +========== + +.. index:: partition, definition + +Partition Manager Definitions +----------------------------- + +A partition is a physically contiguous memory area divided into fixed-size +buffers that can be dynamically allocated and deallocated. + +.. index:: buffers, definition + +Partitions are managed and maintained as a list of buffers. Buffers are +obtained from the front of the partition's free buffer chain and returned to +the rear of the same chain. When a buffer is on the free buffer chain, RTEMS +uses two pointers of memory from each buffer as the free buffer chain. When a +buffer is allocated, the entire buffer is available for application use. +Therefore, modifying memory that is outside of an allocated buffer could +destroy the free buffer chain or the contents of an adjacent allocated buffer. + +.. index:: partition attribute set, building + +Building a Partition Attribute Set +---------------------------------- + +In general, an attribute set is built by a bitwise OR of the desired attribute +components. The set of valid partition attributes is provided in the following +table: + +.. list-table:: + :class: rtems-table + + * - ``RTEMS_LOCAL`` + - local partition (default) + * - ``RTEMS_GLOBAL`` + - global partition + +Attribute values are specifically designed to be mutually exclusive, therefore +bitwise OR and addition operations are equivalent as long as each attribute +appears exactly once in the component list. An attribute listed as a default +is not required to appear in the attribute list, although it is a good +programming practice to specify default attributes. If all defaults are +desired, the attribute ``RTEMS_DEFAULT_ATTRIBUTES`` should be specified on this +call. The attribute_set parameter should be ``RTEMS_GLOBAL`` to indicate that +the partition is to be known globally. |