fsm

Simple Finite-State Machine that can be used with embedded systems

Setup

To work with your project, two dedicated sections have to be added to your linker script. One to store the different states and one other to store the possible state transitions:

.fsm_state :
{
    . = ALIGN(4);
    _fsm_start = .;
    KEEP(*(.fsm_state))           /* fsm state */
    . = ALIGN(4);
    _fsm_end = . ;
} >FLASH

.fsm_trans :
{
    . = ALIGN(4);
    _fsm_trans_start = .;
    KEEP(*(.fsm_trans))           /* fsm transition*/
    . = ALIGN(4);
    _fsm_trans_end = . ;
} >FLASH

Example

In this example, we'll implement the following state machine:

#include "fsm.h"

static struct fsm_ctx g_fsm;

#define EVT1    0x01
#define EVT2    0x02
#define EVT3    0x03


// Custom function to send app event to the FSM
static void app_send_event(uint8_t evt)
{
    // Check if the event needs to be proceed by the state machine
    if(fsm_filter(&g_fsm, evt) == 0)
    {
      if(mcu_in_isr())
      {
        fsm_post_event_isr(&g_fsm, evt);
      }else{
        fsm_post_event(&g_fsm, evt);
      }
    }
}

static int32_t init_state_check(struct fsm_ctx *fsm, uint32_t state)
{
    // Called by the state machine to check if the app allows the state change
    // return -1 to prevent the FSM to move to the state
    printf("init_state_check\n");
    return 0;
}

static int32_t init_exit_state(struct fsm_ctx *fsm, uint32_t evt)
{
    // Called by the state machine when the state exits
    printf("init_exit_state\n");
    return 0;
}

static int32_t init_enter_state(struct fsm_ctx *fsm, uint32_t evt)
{
    // Called by the state machine when the state enters
    printf("init_enter_state\n");

    app_send_event(EVT1);
}

FSM_ADD_STATE(init, FSM_INIT_STATE, init_state_check, init_enter_state, init_exit_state);

static int32_t state1_state_check(struct fsm_ctx *fsm, uint32_t state)
{
    // Called by the state machine to check if the app allows the state change
    // return -1 to prevent the FSM to move to the state
    printf("state1_state_check\n");
    return 0;
}

static int32_t state1_exit_state(struct fsm_ctx *fsm, uint32_t evt)
{
    // Called by the state machine when the state exits
    printf("state1_exit_state\n");
    return 0;
}

static int32_t state1_enter_state(struct fsm_ctx *fsm, uint32_t evt)
{
    // Called by the state machine when the state enters
    printf("state1_enter_state\n");
    delay_ms(1000);
    app_send_event(EVT2);
}

FSM_ADD_STATE(state1, FSM_STATE1, state1_state_check, state1_exit_state, state1_enter_state);


static int32_t state2_state_check(struct fsm_ctx *fsm, uint32_t state)
{
    // Called by the state machine to check if the app allows the state change
    // return -1 to prevent the FSM to move to the state
    printf("state2_state_check\n");
    return 0;
}

static int32_t state2_exit_state(struct fsm_ctx *fsm, uint32_t evt)
{
    // Called by the state machine when the state exits
    printf("state2_exit_state\n");
    return 0;
}

static int32_t state2_enter_state(struct fsm_ctx *fsm, uint32_t evt)
{
    // Called by the state machine when the state enters
    printf("state2_enter_state\n");
    delay_ms(1000);
    app_send_event(EVT3);
}

FSM_ADD_STATE(state2, FSM_STATE2, state2_state_check, state2_exit_state, state2_enter_state);

FSM_ADD_TRANSITION(init_to_state1, FSM_INIT_STATE, FSM_STATE1, EVT1);
FSM_ADD_TRANSITION(state1_to_state2, FSM_STATE1, FSM_STATE2, EVT2);
FSM_ADD_TRANSITION(state2_to_state1, FSM_STATE2, FSM_STATE1, EVT3);

void main(void)
{
    printf("main\n");

    fsm_init(&g_fsm, NULL);
    fsm_process(&g_fsm);
}

Output:

main
init_state_check
init_enter_state
init_exit_state
state1_state_check
state1_enter_state
state1_exit_state
state2_state_check
state2_enter_state
state2_exit_state
state1_state_check
...