This operating system is designed to run on low power embedded devices. It has a pre-emptive scheduling algorithm and offers a POSIX like interface to the userland.
Download the sources with git clone and update the submodules for this project:
git clone https://github.com/sebastianene07/calypso_os.git
git submodule update --init --recursive
Example for building Calypso OS for Norfic NrF5X board:
make config MACHINE_TYPE=nrf5x/nrf52840
make -j
or if we have nrf52832:
make config MACHINE_TYPE=nrf5x/nrf52832
make -j
You can enable different features for your board by using the Kconfig menu selection.
make menuconfig
The above command requires you to have kconfig-mconf installed on your
build machine.
The scheduler is preemptive and each task has a fixed allocated time slot. The scheduler keeps track of two lists g_tcb_waiting_list and g_tcb_list:
g_tcb_waiting_list - holds the tasks waiting for a semaphore
g_tcb_list - holds the tasks in pending state
The g_current_tcb pointer points to the current running task. A task transitions from running to waiting for semaphore when it tries to acquire a semaphore that has a value <= 0. The task is placed in the g_tcb_waiting_list and it's context is saved on the stack.
The allocator is implemented as part of a submodule in s_alloc. It can be configure to run with multipple heap objects depending on the needs. It supports the following operations: s_alloc, s_free, s_realloc and the code is tested in a sample program (main.c) that verify the integrity of the allocated blocks and monitors the fragmentation. The test also verifies that the allocated regions do not overlap. In the current configuration it supports up to 2 ^ 31 - 1 blocks of memory where the block size is defined by the code that it's using the allocator. The allocation is done in O(N) space time (searching through the list of free nodes) whereas the free operation can take O(N^2) because of the block merging and sorting.
The virtual file system contains a tree like structure with nodes that allows us to interract with the system resources. The current nodes are:
"/"
--------------------
| | | | |
dev mnt bin otp home
/ | \
ttyUSB0 rtc0 spi0
A task contains a list of struct opened_resource_s which is essentially
the struct file from Linux and has the same role.
The registered nodes in the virtual file sytem are described by
struct vfs_node_s and these keep informations such as:
- device type
- supported operations
- name
- private data
The open device flow:
open(..) -> vfs_get_matching_node(..) -------
/\ |
Extract the node from the VFS |
and call into ops open_cb(..) |
|
sched_allocate_resource() -----
/\ |
Allocate a new opened_resource_s |
in the calling process. |
Return the index of the |
opened_resource_s structure as |
the file descriptor. |
|
-----------------------------------------------------
|-> vfs_node_open()
/\
Call the appropriate node open function.
The project has a board associated to track issues & request new features:
https://github.com/users/sebastianene07/projects/1#card-30262282
1. Virtual file system support
1.1 Add support for FatFS http://elm-chan.org/fsw/ff/00index_e.html (DONE)
1.1.1 Implement SD/MMC driver (DONE)
1.1.2 Add MTD layer
1.2 Add functional tests for memory allocator (DONE)
1.4 The read/write device flow (DONE)
1.5 Polling from devices
2. Refactorization & Driver lower half/upper half separation (DONE)
3. Tickless kernel
4. Tasks prioritization option
Check out the versatilepb branch to view how the code was ported on the qemu Armv6 emulator. I'm working to add full support on this machine to be able to run it inside qemu.
Contributions are welcome.
You can email me on: Sebastian Ene sebastian.ene07@gmail.com