## RTEMS 5.1 Release Notes

### RTEMS Improvements

In this section, we discuss public API level changes as well as improvements to
the implementation of those API routines.

Public API changes usually fall into one of the following categories:

* Addition of new methods

* Modifications to prototypes

* Deletion of obsoleted methods

Implementation improvements usually fall into one of the following categories:

* Algorithm improvements in execution time or memory usage

* Critical section reduction

### API Changes

* The header file <rtems.h> no longer includes <limits.h> and <string.h>.

* Most services use now statically allocated resources and no longer need
  accounting in the application configuration.

* The work area initialization (RTEMS Work Space and C Program Heap) changed.
  BSPs must provide now a `_Memory_Get()` function.

* POSIX timers and signals are now the only POSIX resources which are enabled
  by the POSIX API.

#### API Additions

* Support for recording of high-frequency events in particular on SMP systems

* Termios supports now generation of signals.

* New fatal sources:

  * `RTEMS_FATAL_SOURCE_EXCEPTION`

  * `RTEMS_FATAL_SOURCE_PANIC`

  * `RTEMS_FATAL_SOURCE_SMP`

  * `RTEMS_FATAL_SOURCE_INVALID_HEAP_FREE`

  * `RTEMS_FATAL_SOURCE_HEAP`

* New chain API function: rtems_chain_get_first_unprotected()

* Add user defined thread names: pthread_setname_np() and pthread_getname_np()

* Support for xz compression/decompression

* Added rtems_scheduler_ident_by_processor()

* Added rtems_scheduler_ident_by_processor_set()

* Added RTEMS_PREDICT_TRUE() and RTEMS_PREDICT_FALSE() for static branch prediction hints

* Added rtems_malloc() and rtems_calloc()

* Added rtems_scheduler_get_maximum_priority()

* Added rtems_scheduler_get_processor()

* Added rtems_scheduler_get_processor_maximum()

#### API Implementation Improvements

* Priority inheritance is now transitive.

* POSIX key destructors are now called during thread restart.

* More robust thread dispatching on SMP and ARM Cortex-M

#### API Deprecations

* `rtems_iterate_over_all_threads()`.  Use `rtems_task_iterate()` instead.

* `rtems_get_current_processor()`.  Use `rtems_scheduler_get_processor()` instead.

* `rtems_get_processor_count()`.  Use `rtems_scheduler_get_processor_maximum()` instead.

* `boolean` is deprecated.  Use `bool` instead.

* `single_precision` is deprecated.  Use `float` instead.

* `double_precision` is deprecated.  Use `double` instead.

* `proc_ptr` is deprecated.  Use a proper function pointer type.

* rtems_context

* rtems_context_fp

* region_information_block

* `rtems_thread_cpu_usage_t` is deprecated. Use `struct timespec` instead.

* `rtems_rate_monotonic_period_time_t` is deprecated. Use `struct timespec` instead.

* `_Copyright_Notice` is deprecated.  Use `rtems_get_copyright_notice()` instead.

* `_RTEMS_version` is deprecated.  Use `rtems_get_version_string()` instead.

* `RTEMS_MAXIMUM_NAME_LENGTH` is deprecated. Use `sizeof(rtems_name)` instead.

* `RTEMS_COMPILER_NO_RETURN_ATTRIBUTE` is deprecated. Use `RTEMS_NO_RETURN` instead.

* `RTEMS_COMPILER_PURE_ATTRIBUTE` is deprecated. Use `RTEMS_PURE` instead.

* `RTEMS_COMPILER_DEPRECATED_ATTRIBUTE` is deprecated. Use `RTEMS_DEPRECATED` instead.

* `RTEMS_COMPILER_UNUSED_ATTRIBUTE` is deprecated. Use `RTEMS_UNUSED` instead.

* `RTEMS_COMPILER_PACKED_ATTRIBUTE` is deprecated. Use `RTEMS_PACKED` instead.

* Including <rtems/system.h> is deprecated.  This header file will be removed in RTEMS 6.

#### API Removals

* `rtems_clock_get()`

* API defined by <rtems/debug.h>

* Task notepads

* Task variables

### SMP Support Improvements

* Reimplemenation of the Multiprocessor Resource Sharing Protocol (MrsP) to
  address performance issues.

* Implementation of the O(m) Independence-Preserving Protocol (OMIP).

* Support for thread pinning (enables support for Epoch Based Reclamation; used
  by libbsd)

* The default SMP scheduler supports now EDF scheduling, one-to-one and
  one-to-all thread to processor affinities, and thread pinning.

* Timers (watchdogs) use now per-processor data structures.

* Improved POSIX key to value look up.

* The Ada runtime supports now SMP configurations.

### Configuration Changes

* All configuration options are now documented.

* Most resources are now statically allocated and no longer use the workspace.

* New configuration options:

    * `CONFIGURE_MAXIMUM_THREAD_NAME_SIZE`

    * `CONFIGURE_MINIMUM_POSIX_THREAD_STACK_SIZE`

    * `CONFIGURE_DIRTY_MEMORY`

    * `CONFIGURE_RECORD_EXTENSIONS_ENABLED`

    * `CONFIGURE_RECORD_FATAL_DUMP_BASE64`

    * `CONFIGURE_RECORD_FATAL_DUMP_BASE64_ZLIB`

    * `CONFIGURE_RECORD_PER_PROCESSOR_ITEMS`

    * `CONFIGURE_VERBOSE_SYSTEM_INITIALIZATION`

    * `CONFIGURE_IMFS_ENABLE_MKFIFO`

    * `CONFIGURE_IMFS_DISABLE_MKNOD_FILE`

* Renamed configuration options:

    * `CONFIGURE_SMP_MAXIMUM_PROCESSORS` to `CONFIGURE_MAXIMUM_PROCESSORS`

    * `CONFIGURE_LIBIO_MAXIMUM_FILE_DESCRIPTORS` to `CONFIGURE_MAXIMUM_FILE_DESCRIPTORS`

* Removed configuration options:

    * `CONFIGURE_SMP_APPLICATION`

    * `CONFIGURE_HAS_OWN_CONFIGURATION_TABLE`

    * `CONFIGURE_HAS_OWN_BDBUF_TABLE`

    * `CONFIGURE_HAS_OWN_DEVICE_DRIVER_TABLE`

    * `CONFIGURE_HAS_OWN_FILESYSTEM_TABLE`

    * `CONFIGURE_HAS_OWN_INIT_TABLE`

    * `CONFIGURE_HAS_OWN_MOUNT_TABLE`

    * `CONFIGURE_HAS_OWN_MULTIPROCESSING_TABLE`

    * `CONFIGURE_POSIX_HAS_OWN_INIT_THREAD_TABLE`

    * `CONFIGURE_DISABLE_SMP_CONFIGURATION`

    * `CONFIGURE_MAXIMUM_DEVICES`

* The helper macro for the clustered scheduler configuration
  `RTEMS_SCHEDULER_EDF_SMP()` has now only one parameter.

## RTEMS Shell Improvements

The following improvements were made to the RTEMS Shell:

* Telnet now supports `joel` script output. Running a `joel` script in a
  telnet session now sees the output. Nested `joel` scripts also output to the
  telnet session.

## General

* The system initialization is now performed by system initialization handlers
  registered in a special linker set (similar to global constructors in C++).

* API header files have been collected from the various locations in the RTEMS
  source tree and placed under `cputkit/include` and for BSPs under
  `bsps/include`. There is no header pre-install phase when building RTEMS.

* Improved parallel build performance. Nested `make` calls now run in
  parallel.

* Added support for the RISC-V 32-bit and 64-bit architecture.

* Added support for the 64-bit PowerPC architecture using the ELFv2 ABI.

* Synchronized support for Journalling Flash File System, Version 2 (JFFS2)
  with Linux 4.17.

* Import of libfdt from device tree compiler project.

* Added `libdebugger`, a thread aware GDB debug server with TCP transport
  support. Currently the supported architectures are i386 and ARM. The ARM
  support is experimental.

* Most BSP use now function and data sections to support the linker garbage
  collection.

* This is the last release of RTEMS with the `autoconf`/`automake` build
  system. RTEMS will be moving to a `waf` based build system driven from YAML
  specifications files. The effort is part of the on-going wotk in the RTEMS
  project to support qualification of the operating system.

## Architectures

Removed obsolete architectures:

* AVR

* H8300

* M32C

* M32R

Obsoleted architectures:

* Epiphany

* PowerPC SPE

## BSPs and Device Drivers

* General

    * BSP source code moved from `c/src/lib/libbsp` to `bsps` in the
      source tree. The configure and some other related pieces are still held in
      the original path.

* New BSPs

    * BSPs for ARM

        * `atsamv` - Microchip (former Atmel) SAM V71 series

        * `xilinx-zynqmp` - Xilinx Zynq UltraScale+ MPSoC platform

    * BSPs for RISC-V

        * `riscv` - Family of generic BSPs

        * `griscv` - BSP based on the GRLIB

* Significant updates to existing BSPs

    * `powerpc/qoriq`: 64-bit support

* Removal of obsoleted BSPs

    * `arm/gdbarmsim`

    * `arm/nds`

    * `arm/gp32`

    * `arm/ep1a`

    * `arm/score603e`

    * `m68k/idp`

* Obsoleted BSPs

    * `m68k/gen68302`

    * `m68k/ods68302`

    * `powerpc/brs5l`

    * `powerpc/brs6l`

    * `powerpc/dp2`

    * `powerpc/mbx8xx`

    * `powerpc/mpc5566evb_spe`

    * `powerpc/mpc5643l_dpu`

    * `powerpc/mpc5643l_evb`

    * `powerpc/mpc5674f_ecu508_app`

    * `powerpc/mpc5674f_ecu508_boot`

    * `powerpc/mpc5674fevb_spe`

    * `powerpc/mpc5674f_rsm6`

* Drivers

    * Drivers for `getentropy()`

    * New I2C device driver framework supporting the Linux user-space API

    * New SPI device driver framework supporting the Linux user-space API

## Newlib Changes

* time_t is now 64-bit to adress the year 2038 problem.

* General improvements in the feature test macros support.

* Newlib internal locks are now supported, e.g. for FILE objects.

* The standard input, output, and error FILE objects are now global and no
  longer thread-specific.

* Added support for C++17 std::aligned_alloc

## Ecosystem

* RSB support to build a BSP software stack of tools, kernel, libbsd, and
  supported 3rd party packages.

* RTEMS Tester (`rtems-test`) support for DHCP/TFTP target hardware testing.

* RTEMS Trace addition of a new trace record support for target tracing.

* RTEMS Bootimage, a tool to portably create SD card images.