How Mapping Tables Simplify Serial Port Parsing and UI Navigation in Embedded C

Mapping Table in Serial Port Data Parsing

The article first defines a simple structure to associate a command string with its handling function:

typedef struct {
    char CMD[CMDLen];
    unsigned char (*cmd_operate)(char *data);
} Usart_Tab;

An array of these structures, InstructionList, maps each command to its corresponding function:

static const Usart_Tab InstructionList[CMDMax] = {
    {"PWON", PowOn},
    {"PWOFF", PowOff},
    {"HDCP", HdcpOnOff},
    {"/V", QueryKaVersion},
    {"EDIDUpgrade", UpdataEDID},
    {"Psave", Psave},
    {"Precall", Precall},
    {"Pclear", Pclear},
};

The parsing function DataAnalysis iterates over the table, compares the incoming buffer with each command, and invokes the matched handler:

unsigned char DataAnalysis(char *buf) {
    unsigned char i, Result;
    char *NEXT = NULL;
    for (i = 0; i < CMDMax; i++) {
        NEXT = StrCmp(buf, (char *)InstructionList[i].CMD);
        if (NEXT != NULL) {
            usartfuncp = InstructionList[i].cmd_operate;
            Result = (*usartfuncp)(NEXT);
        }
    }
    return Result;
}

Mapping Table in UI Design

For UI navigation, an enumeration defines menu scenes:

typedef enum {
    stage1 = 0,
    stage2,
    stage3,
    stage4,
    stage5,
    stage6,
    stage7,
    stage8,
    stage9,
} SCENE;

A structure stores the handler for the current scene and the indices of neighboring scenes:

typedef struct {
    void (*current_operate)(); // handler for the scene
    SCENE Index;               // label of the scene
    SCENE Up;                  // scene when Up key is pressed
    SCENE Down;                // scene when Down key is pressed
    SCENE Right;               // scene when Right key is pressed
    SCENE Left;                // scene when Left key is pressed
} STAGE_TAB;

The navigation table stage_tab links each scene to its handler and neighbor indices:

STAGE_TAB stage_tab[] = {
    {Stage1_Handler, stage1, stage4, stage7, stage3, stage2},
    {Stage2_Handler, stage2, stage5, stage8, stage1, stage3},
    {Stage3_Handler, stage3, stage6, stage9, stage2, stage1},
    {Stage4_Handler, stage4, stage7, stage1, stage6, stage5},
    {Stage5_Handler, stage5, stage8, stage2, stage4, stage6},
    {Stage6_Handler, stage6, stage9, stage3, stage5, stage4},
    {Stage7_Handler, stage7, stage1, stage4, stage9, stage8},
    {Stage8_Handler, stage8, stage2, stage5, stage7, stage9},
    {Stage9_Handler, stage9, stage3, stage6, stage8, stage7},
};

Two variables keep track of the current and previous scenes:

char current_stage = stage1;
char prev_stage = current_stage;

When the Up key is pressed, the current scene is updated using the Up field of the table:

current_stage = stage_tab[current_stage].Up;

If the scene has changed, the corresponding handler is executed and the previous scene variable is updated:

if (current_stage != prev_stage) {
    stage_tab[current_stage].current_operate();
    prev_stage = current_stage;
}

The article concludes with a brief note that the author is sharing these essential programming resources for free, but the technical content above stands on its own as a practical guide for using mapping tables in both serial communication and UI state management.