Software Bus — publish/subscribe message router implementation. More...

#include "icarus/icarus.h"
#include "icarus/svc.h"
#include <string.h>

Data Structures
struct	sb_route_t
	Single route entry: one msg_id → up to SB_MAX_SUBS_PER_MSG pipes. More...

Functions
static sb_route_t *	find_route (sb_msg_id_t msg_id)
	Find the route entry for `msg_id`.

static sb_route_t *	alloc_route (void)
	Allocate a fresh route slot.

void	__sb_init (void)
	Privileged implementation of sb_init().

bool	__sb_subscribe (sb_msg_id_t msg_id, uint8_t pipe_idx)
	Privileged implementation of sb_subscribe().

bool	__sb_unsubscribe (sb_msg_id_t msg_id, uint8_t pipe_idx)
	Privileged implementation of sb_unsubscribe().

uint8_t	__sb_publish (sb_msg_id_t msg_id, const uint8_t *data, uint8_t len)
	Privileged implementation of sb_publish().

uint8_t	__sb_subscriber_count (sb_msg_id_t msg_id)
	Privileged implementation of sb_subscriber_count().

uint8_t	__sb_route_count (void)
	Privileged implementation of sb_route_count().

void	sb_init (void)
	Initialize the software bus via SVC gate.

bool	sb_subscribe (sb_msg_id_t msg_id, uint8_t pipe_idx)
	Subscribe a pipe to a message ID via SVC gate.

bool	sb_unsubscribe (sb_msg_id_t msg_id, uint8_t pipe_idx)
	Remove a subscription via SVC gate.

uint8_t	sb_publish (sb_msg_id_t msg_id, const uint8_t *data, uint8_t len)
	Publish a message to all subscribers via SVC gate.

uint8_t	sb_subscriber_count (sb_msg_id_t msg_id)
	Return the subscriber count for a message ID via SVC gate.

uint8_t	sb_route_count (void)
	Return the total route count via SVC gate.

Variables
static sb_route_t	routes [32]
	Route table — privileged DTCM, zero wait-state.

static uint8_t	route_used
	Number of route slots in use.

Detailed Description

Software Bus — publish/subscribe message router implementation.

Version: 0.1.0

Static routing table mapping msg_id → pipe_idx[]. Publishing iterates subscribers and enqueues into each pipe that has space.

All mutable state lives in DTCM_DATA_PRIV (privileged-only, zero wait-state on Cortex-M7). All functions are placed in ITCM_FUNC for zero wait-state instruction fetch. Public access goes through SVC call gates; the __-prefixed functions are the privileged implementations.

Thread safety:: Every public function issues an SVC instruction to execute the privileged implementation in handler mode. The SVC handler is non-preemptible, guaranteeing atomic access to the route table.

Author: Souham Biswas

Date: 2026

Copyright: Copyright 2025-2026 Souham Biswas https://github.com/ironhide23586/icarus-os-core Licensed under the Apache License, Version 2.0

Definition in file sb.c.

Function Documentation

◆ __sb_init()

void __sb_init ( void )

Privileged implementation of sb_init().

Zeroes the entire route table and resets the used counter.

Definition at line 93 of file sb.c.

References route_used, and routes.

Referenced by sb_init(), and SVC_Handler_C().

◆ __sb_publish()

uint8_t __sb_publish	(	sb_msg_id_t	msg_id,
		const uint8_t *	data,
		uint8_t	len
	)

Privileged implementation of sb_publish().

Parameters

[in]	msg_id	Message identifier.
[in]	data	Payload bytes.
[in]	len	Payload length.

Returns: Number of subscribers successfully enqueued to.

Iterates all subscribers for msg_id. For each pipe, checks capacity via pipe_can_enqueue() before writing. Pipes that are full are silently skipped (best-effort).

Definition at line 173 of file sb.c.

References __pipe_can_enqueue(), __pipe_write_bytes(), sb_route_t::count, find_route(), and sb_route_t::pipes.

Referenced by sb_publish(), and SVC_Handler_C().

◆ __sb_route_count()

uint8_t __sb_route_count ( void )

Privileged implementation of sb_route_count().

Returns: Number of distinct msg_ids with at least one subscriber.

Definition at line 209 of file sb.c.

References route_used.

Referenced by sb_route_count(), and SVC_Handler_C().

◆ __sb_subscribe()

bool __sb_subscribe	(	sb_msg_id_t	msg_id,
		uint8_t	pipe_idx
	)

Privileged implementation of sb_subscribe().

Parameters

[in]	msg_id	Message identifier.
[in]	pipe_idx	Kernel pipe index to bind.

Return values

true	Subscription added.
false	Table full, subscriber limit hit, or duplicate pair.

If no route exists for msg_id a new slot is allocated. Duplicate (msg_id, pipe_idx) pairs are rejected to prevent double-delivery.

Definition at line 110 of file sb.c.

References alloc_route(), sb_route_t::count, find_route(), sb_route_t::msg_id, sb_route_t::pipes, and SB_MAX_SUBS_PER_MSG.

Referenced by sb_subscribe(), and SVC_Handler_C().

◆ __sb_subscriber_count()

uint8_t __sb_subscriber_count ( sb_msg_id_t msg_id )

Privileged implementation of sb_subscriber_count().

Parameters

[in] msg_id Message identifier.

Returns: Active subscriber count, or 0 if no route exists.

Definition at line 200 of file sb.c.

References sb_route_t::count, and find_route().

Referenced by sb_subscriber_count(), and SVC_Handler_C().

◆ __sb_unsubscribe()

bool __sb_unsubscribe	(	sb_msg_id_t	msg_id,
		uint8_t	pipe_idx
	)

Privileged implementation of sb_unsubscribe().

Parameters

[in]	msg_id	Message identifier.
[in]	pipe_idx	Pipe to remove.

Return values

true	Subscription found and removed (last-swap compaction).
false	No matching subscription.

Definition at line 144 of file sb.c.

References sb_route_t::count, find_route(), and sb_route_t::pipes.

Referenced by sb_unsubscribe(), and SVC_Handler_C().

◆ alloc_route()

static sb_route_t * alloc_route ( void )

static

Allocate a fresh route slot.

Returns: Pointer to new slot, or NULL if table is full.

Note: Caller must hold critical section.

Definition at line 75 of file sb.c.

References route_used, routes, SB_MAX_ROUTES, and sb_route_t::used.

Referenced by __sb_subscribe().

◆ find_route()

static sb_route_t * find_route ( sb_msg_id_t msg_id )

static

Find the route entry for msg_id.

Returns: Pointer to route, or NULL if not found.

Note: Caller must hold critical section.

Definition at line 61 of file sb.c.

References route_used, and routes.

Referenced by __sb_publish(), __sb_subscribe(), __sb_subscriber_count(), and __sb_unsubscribe().

◆ sb_init()

void sb_init ( void )

Initialize the software bus via SVC gate.

Initialize the software bus.

Clears all routes in privileged mode.

Definition at line 221 of file sb.c.

References __sb_init(), and SVC_SB_INIT.

◆ sb_publish()

uint8_t sb_publish	(	sb_msg_id_t	msg_id,
		const uint8_t *	data,
		uint8_t	len
	)

Publish a message to all subscribers via SVC gate.

Publish a message to all subscribers of msg_id.

Parameters

[in]	msg_id	Message identifier.
[in]	data	Payload bytes.
[in]	len	Payload length.

Returns: Number of subscribers successfully enqueued to.

Definition at line 288 of file sb.c.

References __sb_publish(), and SVC_SB_PUBLISH.

◆ sb_route_count()

uint8_t sb_route_count ( void )

Return the total route count via SVC gate.

Return the total number of route entries in use.

Returns: Number of distinct msg_ids with at least one subscriber.

Definition at line 334 of file sb.c.

References __sb_route_count(), and SVC_SB_ROUTE_COUNT.

◆ sb_subscribe()

bool sb_subscribe	(	sb_msg_id_t	msg_id,
		uint8_t	pipe_idx
	)

Subscribe a pipe to a message ID via SVC gate.

Subscribe a pipe to a message ID.

Parameters

[in]	msg_id	Message identifier.
[in]	pipe_idx	Kernel pipe index.

Return values

true	Subscription added.
false	Table full, limit hit, or duplicate.

Definition at line 236 of file sb.c.

References __sb_subscribe(), and SVC_SB_SUBSCRIBE.

◆ sb_subscriber_count()

uint8_t sb_subscriber_count ( sb_msg_id_t msg_id )

Return the subscriber count for a message ID via SVC gate.

Return the number of active subscriptions for a message ID.

Parameters

[in] msg_id Message identifier.

Returns: Active subscriber count, or 0 if no route exists.

Definition at line 313 of file sb.c.

References __sb_subscriber_count(), and SVC_SB_SUBSCRIBER_COUNT.

◆ sb_unsubscribe()

bool sb_unsubscribe	(	sb_msg_id_t	msg_id,
		uint8_t	pipe_idx
	)

Remove a subscription via SVC gate.

Remove a subscription.

Parameters

[in]	msg_id	Message identifier.
[in]	pipe_idx	Pipe to unsubscribe.

Return values

true	Subscription found and removed.
false	No matching subscription.

Definition at line 262 of file sb.c.

References __sb_unsubscribe(), and SVC_SB_UNSUBSCRIBE.

Variable Documentation

◆ route_used

uint8_t route_used

static

Number of route slots in use.

Definition at line 50 of file sb.c.

Referenced by __sb_init(), __sb_route_count(), alloc_route(), and find_route().

◆ routes

sb_route_t routes[32]

static

Route table — privileged DTCM, zero wait-state.

Definition at line 47 of file sb.c.

Referenced by __sb_init(), alloc_route(), and find_route().

Data Structures

Functions

Variables

Detailed Description

Function Documentation

◆ __sb_init()

◆ __sb_publish()

◆ __sb_route_count()

◆ __sb_subscribe()

◆ __sb_subscriber_count()

◆ __sb_unsubscribe()

◆ alloc_route()

◆ find_route()

◆ sb_init()

◆ sb_publish()

◆ sb_route_count()

◆ sb_subscribe()

◆ sb_subscriber_count()

◆ sb_unsubscribe()

Variable Documentation

◆ route_used

◆ routes