Более нормальный подход можно увидеть тоже для контроллера, к примеру, в SoftModemLibrary для dsPic'а:
dsPIC30F Soft Modem Library\V.22bis Modem_R1.0\source\ATCMD\AT_Cmds.c

Вот выдержка (к такому разбору нужно стремится, т.к. это универсальный и стандартный подход по разбору выражений, ну или похож на него):

/*-------------------------------------------------------------------------
 Function Name: InterpretCommand
 Description  : This function is used to interpret the AT command
 Input        : AT_Conmmand Structure pointer
 Output       : None 
--------------------------------------------------------------------------*/
void InterpretCommand(AT_COMMAND *atcmdptr, INT CHNID)
{
    INT i;
    INT Quiet1, Verbose1;
    UCHAR TempBuf[6];
    Quiet1 = atcmdptr->commands[ATQ];
    Verbose1 = atcmdptr->commands[ATV];
    switch(atcmdptr->KeyBuf[0])
    {
// According to the first character of the command it will store the command
// characters from command buffer to current buffer.
        case 'A':
        case 'a':
            for(i=0;i<=atcmdptr->KeyNo-1;i++)
            {
                atcmdptr->aiCurBuf[i] = atcmdptr->KeyBuf[i];
            }
            atcmdptr->icount = atcmdptr->KeyNo;
            ProcessFunction(atcmdptr,atcmdptr->aiCurBuf,atcmdptr->icount, CHNID);
            break;
        default:
        
        for(i=0;i<=atcmdptr->KeyNo-1;i++)
            {
                atcmdptr->aiprevbuf[i] = atcmdptr->KeyBuf[i];
            }
            atcmdptr->PrevCmdCntr=atcmdptr->KeyNo;
            SendResponse(atcmdptr,COMERROR);
            break;
    }
}
/*-------------------------------------------------------------------------
 Function Name: ProcessFunction
 Description  : This function is used to process and execute the required
                functionality of the lower layer
 Input        : AT_Conmmand Structure pointer,Command Buf Pointer, character
                count
 Output       : None 
--------------------------------------------------------------------------*/
void ProcessFunction(AT_COMMAND *atcmdptr, CHAR *aiCurBuf, CHAR icount, CHAR CHNID)
{
    INT i=0,cntr=2, val,SValue,SIndex;
    INT ch,a1,a2;
    INT QuietControl, VerboseControl;
    CHAR ch1;
    UINT MsgParams[25];
    QuietControl = atcmdptr->commands[ATQ];
    VerboseControl = atcmdptr->commands[ATV];
    // read the 2nd character for slash (/)
    ch = aiCurBuf[1];
    //check for / after A if not / copy aiCurBuf to prevbuf
    if(ch != '/')
    {
        for(i=0;i<=icount;i++)
        {
           atcmdptr->aiprevbuf[i] = aiCurBuf[i];
        }
        // copy the number of characters in icount to prevcntr
        atcmdptr->PrevCmdCntr = icount;
    }
    else
    {
        // Repeat command then copy the recent command from
        // prevbuf to aiCurBuf
        for(i=0;i<=atcmdptr->PrevCmdCntr;i++)
        {
          aiCurBuf[i] = atcmdptr->aiprevbuf[i];
        }
        // Copy the PrevCmdCntr characters to icount for analyzing
        atcmdptr->icount = atcmdptr->PrevCmdCntr;
    }
    //if icount is 2 then we have AT command then send
    //OK response to DTE.
    if(atcmdptr->aiCurBuf[1] != '/' && atcmdptr->aiCurBuf[1] != 't' && atcmdptr->aiCurBuf[1] != 'T')
    {
        SendResponse(atcmdptr,COMERROR);
        return;
    }

    if(atcmdptr->icount == 2)
    {
        SendResponse(atcmdptr,COMOK);
     //   return;
    }

    // if the command is 3 characters i.e., ATA,ATH,AT+,ATD
    // Store the current address of aiCurBuf to aiCurBuf,to fetch
    // 3rd character
    aiCurBuf = &aiCurBuf[2];