atchannel.c解析

/* //device/system/reference-ril/atchannel.c
**
** Copyright 2006, The Android Open Source Project
**
** Licensed under the Apache License, Version 2.0 (the "License");
** you may not use this file except in compliance with the License.
** You may obtain a copy of the License at
**
**     http://www.apache.org/licenses/LICENSE-2.0
**
** Unless required by applicable law or agreed to in writing, software
** distributed under the License is distributed on an "AS IS" BASIS,
** WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
** See the License for the specific language governing permissions and
** limitations under the License.
*/

#include "atchannel.h"
#include "at_tok.h"

#include <stdio.h>
#include <string.h>
#include <pthread.h>
#include <ctype.h>
#include <stdlib.h>
#include <errno.h>
#include <fcntl.h>
#include <sys/time.h>
#include <time.h>
#include <unistd.h>

#define LOG_NDEBUG 0
#define LOG_TAG "AT"
#include <utils/Log.h>

#ifdef HAVE_ANDROID_OS
/* for IOCTL's */
#include <linux/omap_csmi.h>
#endif /*HAVE_ANDROID_OS*/

#include "misc.h"

#ifdef HAVE_ANDROID_OS
#define USE_NP 1
#endif /* HAVE_ANDROID_OS */


#define NUM_ELEMS(x) (sizeof(x)/sizeof(x[0]))

#define MAX_AT_RESPONSE (8 * 1024)
#define HANDSHAKE_RETRY_COUNT 8
#define HANDSHAKE_TIMEOUT_MSEC 250

static pthread_t s_tid_reader;
static int s_fd = -1;    /* fd of the AT channel */
static ATUnsolHandler s_unsolHandler;

/* for input buffering */
//主要是android的libc没有buffering，这个地方模拟出一个buffering的环境
//存储readline函数read到的数据
static char s_ATBuffer[MAX_AT_RESPONSE+1];
static char *s_ATBufferCur = s_ATBuffer;

static int s_ackPowerIoctl; /* true if TTY has android byte-count
                                handshake for low power*/
static int s_readCount = 0;

#if AT_DEBUG
void  AT_DUMP(const char*  prefix, const char*  buff, int  len)
{
    if (len < 0)
        len = strlen(buff);
    LOGD("%.*s", len, buff);
}
#endif

/*
 * for current pending command
 * these are protected by s_commandmutex
 */

static pthread_mutex_t s_commandmutex = PTHREAD_MUTEX_INITIALIZER;
static pthread_cond_t s_commandcond = PTHREAD_COND_INITIALIZER;

static ATCommandType s_type;
static const char *s_responsePrefix = NULL;
static const char *s_smsPDU = NULL;
static ATResponse *sp_response = NULL;

static void (*s_onTimeout)(void) = NULL;
static void (*s_onReaderClosed)(void) = NULL;
static int s_readerClosed;

static void onReaderClosed();
static int writeCtrlZ (const char *s);
static int writeline (const char *s);

#ifndef USE_NP
static void setTimespecRelative(struct timespec *p_ts, long long msec)
{
    struct timeval tv;

    gettimeofday(&tv, (struct timezone *) NULL);

    /* what's really funny about this is that I know
       pthread_cond_timedwait just turns around and makes this
       a relative time again */
    p_ts->tv_sec = tv.tv_sec + (msec / 1000);
    p_ts->tv_nsec = (tv.tv_usec + (msec % 1000) * 1000L ) * 1000L;
}
#endif /*USE_NP*/

static void sleepMsec(long long msec)
{
    struct timespec ts;
    int err;

    ts.tv_sec = (msec / 1000);
    ts.tv_nsec = (msec % 1000) * 1000 * 1000;

    do {
        err = nanosleep (&ts, &ts);
    } while (err < 0 && errno == EINTR);
}



/** add an intermediate response to sp_response*/
static void addIntermediate(const char *line)
{
    ATLine *p_new;

    p_new = (ATLine  *) malloc(sizeof(ATLine));

    p_new->line = strdup(line);

    /* note: this adds to the head of the list, so the list
       will be in reverse order of lines received. the order is flipped
       again before passing on to the command issuer */
    p_new->p_next = sp_response->p_intermediates;
    sp_response->p_intermediates = p_new;
}


/**
 * returns 1 if line is a final response indicating error
 * See 27.007 annex B
 * WARNING: NO CARRIER and others are sometimes unsolicited

 如果某一行response是以下面的字符串开头，那么说明是一个
 final response(不是intermedia response)，并且是失败的最终回复
 */
static const char * s_finalResponsesError[] = {
    "ERROR",
    "+CMS ERROR:",
    "+CME ERROR:",
    "NO CARRIER", /* sometimes! */
    "NO ANSWER",
    "NO DIALTONE",
};
static int isFinalResponseError(const char *line)
{
    size_t i;

    for (i = 0 ; i < NUM_ELEMS(s_finalResponsesError) ; i++) {
        if (strStartsWith(line, s_finalResponsesError[i])) {
            return 1;
        }
    }

    return 0;
}

/**
 * returns 1 if line is a final response indicating success
 * See 27.007 annex B
 * WARNING: NO CARRIER and others are sometimes unsolicited
 
  如果某一行response是以下面的字符串开头，那么说明是一个
 final response(不是intermedia response)，并且是一个成功的最终回复
 
 */
static const char * s_finalResponsesSuccess[] = {
    "OK",
    "CONNECT"       /* some stacks start up data on another channel */
};
static int isFinalResponseSuccess(const char *line)
{
    size_t i;

    for (i = 0 ; i < NUM_ELEMS(s_finalResponsesSuccess) ; i++) {
        if (strStartsWith(line, s_finalResponsesSuccess[i])) {
            return 1;
        }
    }

    return 0;
}

/**
 * returns 1 if line is a final response, either  error or success
 * See 27.007 annex B
 * WARNING: NO CARRIER and others are sometimes unsolicited
 */
static int isFinalResponse(const char *line)
{
    return isFinalResponseSuccess(line) || isFinalResponseError(line);
}


/**
 * returns 1 if line is the first line in (what will be) a two-line
 * SMS unsolicited response

 sms的response是以下面的字符串开头的
 */
static const char * s_smsUnsoliciteds[] = {
    "+CMT:",
    "+CDS:",
    "+CBM:"
};
static int isSMSUnsolicited(const char *line)
{
    size_t i;

    for (i = 0 ; i < NUM_ELEMS(s_smsUnsoliciteds) ; i++) {
        if (strStartsWith(line, s_smsUnsoliciteds[i])) {
            return 1;
        }
    }

    return 0;
}


/** 
assumes s_commandmutex is held

把Final response赋值到sp_response的finaResponse字段
*/
static void handleFinalResponse(const char *line)
{
    sp_response->finalResponse = strdup(line);

    pthread_cond_signal(&s_commandcond);
}

static void handleUnsolicited(const char *line)
{
    if (s_unsolHandler != NULL) {
        s_unsolHandler(line, NULL);
    }
}

//处理一行response
static void processLine(const char *line)
{
    pthread_mutex_lock(&s_commandmutex);

/*
如果sp_response为NULL那说明这是个unsolicited response，因为在onRequest里面
有这句: sp_response = at_response_new();
*/
    if (sp_response == NULL) {
        /* no command pending
        没有正在处理的command
        */
        handleUnsolicited(line);
    } else if (isFinalResponseSuccess(line)) {
    	/*把sp_response的success变量赋值为1，并且把数据拷贝到sp_response的
	的finalResponse字段
    	*/
        sp_response->success = 1;
        handleFinalResponse(line);
    } else if (isFinalResponseError(line)) {
        	/*把sp_response的success变量赋值为1，并且把数据拷贝到sp_response的
	的finalResponse字段
    	*/
        sp_response->success = 0;
        handleFinalResponse(line);
    } else if (s_smsPDU != NULL && 0 == strcmp(line, "> ")) {
        // See eg. TS 27.005 4.3
        // Commands like AT+CMGS have a "> " prompt
        writeCtrlZ(s_smsPDU);
        s_smsPDU = NULL;
    } else
    //否则，可能是一些intermediate的response，处理之
    switch (s_type) {
        case NO_RESULT:
            handleUnsolicited(line);
            break;
        case NUMERIC: //只有一个intermediate的response，并且是以数字开头
            if (sp_response->p_intermediates == NULL
                && isdigit(line[0])
            ) {
                addIntermediate(line);
            } else {
            	/*
			虽然我们的sp_response不为空，我们有正在处理的command，但
			也还是有可能在这个时间里面收到unsolicited response的
		*/
                /* either we already have an intermediate response or
                   the line doesn't begin with a digit */
                handleUnsolicited(line);
            }
            break;
        case SINGLELINE: //只有一个intermediate response,并且是以指定的字符串开头(s_responsePrefix)
            if (sp_response->p_intermediates == NULL
                && strStartsWith (line, s_responsePrefix)
            ) {
                addIntermediate(line);
            } else {
                        	/*
			虽然我们的sp_response不为空，我们有正在处理的command，但
			也还是有可能在这个时间里面收到unsolicited response的
		*/
                /* we already have an intermediate response */
                handleUnsolicited(line);
            }
            break;
        case MULTILINE: //有多行的intermediate response
        //多行的response必须以指定的字符串开头(s_responsePrefix)
            if (strStartsWith (line, s_responsePrefix)) {
                addIntermediate(line);
            } else {
                handleUnsolicited(line);
            }
        break;

        default: /* this should never be reached */
            LOGE("Unsupported AT command type %d\n", s_type);
            handleUnsolicited(line);
        break;
    }

    pthread_mutex_unlock(&s_commandmutex);
}


/**
 * Returns a pointer to the end of the next line
 * special-cases the "> " SMS prompt
 *
 * returns NULL if there is no complete line
 */
static char * findNextEOL(char *cur)
{
    if (cur[0] == '>' && cur[1] == ' ' && cur[2] == '\0') {
        /* SMS prompt character...not \r terminated */
        return cur+2;
    }

    // Find next newline
    while (*cur != '\0' && *cur != '\r' && *cur != '\n') cur++;

    return *cur == '\0' ? NULL : cur;
}


/**
 * Reads a line from the AT channel, returns NULL on timeout.
 * Assumes it has exclusive read access to the FD
 *
 * This line is valid only until the next call to readline
 *
 * This function exists because as of writing, android libc does not
 * have buffered stdio.
 */
//读取一行数据，AT指令的response每一行都是以<CR><LF>结尾的
static const char *readline()
{
    ssize_t count;

    char *p_read = NULL;
    char *p_eol = NULL;
    char *ret;

    /* this is a little odd. I use *s_ATBufferCur == 0 to
     * mean "buffer consumed completely". If it points to a character, than
     * the buffer continues until a \0
     */
    if (*s_ATBufferCur == '\0') {
        /* empty buffer */
        s_ATBufferCur = s_ATBuffer;
        *s_ATBufferCur = '\0';
        p_read = s_ATBuffer;
    } else {   /* *s_ATBufferCur != '\0' */
        /* there's data in the buffer from the last read */

        // skip over leading newlines
        while (*s_ATBufferCur == '\r' || *s_ATBufferCur == '\n')
            s_ATBufferCur++;

        p_eol = findNextEOL(s_ATBufferCur);

        if (p_eol == NULL) {
            /* a partial line. move it up and prepare to read more */
            size_t len;

            len = strlen(s_ATBufferCur);

            memmove(s_ATBuffer, s_ATBufferCur, len + 1);
            p_read = s_ATBuffer + len;
            s_ATBufferCur = s_ATBuffer;
        }
        /* Otherwise, (p_eol !- NULL) there is a complete line  */
        /* that will be returned the while () loop below        */
    }

    while (p_eol == NULL) {
        if (0 == MAX_AT_RESPONSE - (p_read - s_ATBuffer)) {
            LOGE("ERROR: Input line exceeded buffer\n");
            /* ditch buffer and start over again */
            s_ATBufferCur = s_ATBuffer;
            *s_ATBufferCur = '\0';
            p_read = s_ATBuffer;
        }

        do {
            count = read(s_fd, p_read,
                            MAX_AT_RESPONSE - (p_read - s_ATBuffer));
        } while (count < 0 && errno == EINTR);

        if (count > 0) {
            AT_DUMP( "<< ", p_read, count );
            s_readCount += count;

            p_read[count] = '\0';

            // skip over leading newlines
            while (*s_ATBufferCur == '\r' || *s_ATBufferCur == '\n')
                s_ATBufferCur++;

            p_eol = findNextEOL(s_ATBufferCur);
            p_read += count;
        } else if (count <= 0) {
            /* read error encountered or EOF reached */
            if(count == 0) {
                LOGD("atchannel: EOF reached");
            } else {
                LOGD("atchannel: read error %s", strerror(errno));
            }
            return NULL;
        }
    }

    /* a full line in the buffer. Place a \0 over the \r and return */

    ret = s_ATBufferCur;
    *p_eol = '\0';
    s_ATBufferCur = p_eol + 1; /* this will always be <= p_read,    */
                              /* and there will be a \0 at *p_read */

    LOGD("AT< %s\n", ret);
    return ret;
}

//readerLoop出现了读取数据的异常，关闭掉fd
static void onReaderClosed()
{
    if (s_onReaderClosed != NULL && s_readerClosed == 0) {

        pthread_mutex_lock(&s_commandmutex);

        s_readerClosed = 1;

        pthread_cond_signal(&s_commandcond);

        pthread_mutex_unlock(&s_commandmutex);

        s_onReaderClosed();
    }
}


static void *readerLoop(void *arg)
{
    for (;;) {
        const char * line;

        line = readline();

        if (line == NULL) {
            break;
        }

        if(isSMSUnsolicited(line)) {
            char *line1;
            const char *line2;

            // The scope of string returned by 'readline()' is valid only
            // till next call to 'readline()' hence making a copy of line
            // before calling readline again.
            line1 = strdup(line);
            line2 = readline();

            if (line2 == NULL) {
                break;
            }

            if (s_unsolHandler != NULL) {
                s_unsolHandler (line1, line2);
            }
            free(line1);
        } else {
            processLine(line);
        }

#ifdef HAVE_ANDROID_OS
        if (s_ackPowerIoctl > 0) {
            /* acknowledge that bytes have been read and processed */
            ioctl(s_fd, OMAP_CSMI_TTY_ACK, &s_readCount);
            s_readCount = 0;
        }
#endif /*HAVE_ANDROID_OS*/
    }

    onReaderClosed();

    return NULL;
}

/**
 * Sends string s to the radio with a \r appended.
 * Returns AT_ERROR_* on error, 0 on success
 *
 * This function exists because as of writing, android libc does not
 * have buffered stdio.
 */
 //写入一行数据到fd里面，并且在结尾加上一个\r(也就是<CR>)
static int writeline (const char *s)
{
    size_t cur = 0;
    size_t len = strlen(s);
    ssize_t written;

    if (s_fd < 0 || s_readerClosed > 0) {
        return AT_ERROR_CHANNEL_CLOSED;
    }

    LOGD("AT> %s\n", s);

    AT_DUMP( ">> ", s, strlen(s) );

    /* the main string */
    while (cur < len) {
        do {
            written = write (s_fd, s + cur, len - cur);
        } while (written < 0 && errno == EINTR);

        if (written < 0) {
            return AT_ERROR_GENERIC;
        }

        cur += written;
    }

    /* the \r  */

    do {
        written = write (s_fd, "\r" , 1);
    } while ((written < 0 && errno == EINTR) || (written == 0));

    if (written < 0) {
        return AT_ERROR_GENERIC;
    }

    return 0;
}

//response强制需要朝modem里面写入数据，一般是SMS的pdu
static int writeCtrlZ (const char *s)
{
    size_t cur = 0;
    size_t len = strlen(s);
    ssize_t written;

    if (s_fd < 0 || s_readerClosed > 0) {
        return AT_ERROR_CHANNEL_CLOSED;
    }

    LOGD("AT> %s^Z\n", s);

    AT_DUMP( ">* ", s, strlen(s) );

    /* the main string */
    while (cur < len) {
        do {
            written = write (s_fd, s + cur, len - cur);
        } while (written < 0 && errno == EINTR);

        if (written < 0) {
            return AT_ERROR_GENERIC;
        }

        cur += written;
    }

    /* the ^Z  */

    do {
        written = write (s_fd, "\032" , 1);
    } while ((written < 0 && errno == EINTR) || (written == 0));

    if (written < 0) {
        return AT_ERROR_GENERIC;
    }

    return 0;
}

//通常是在at_send_command_full_nolock出现问题的时候调用，清除掉
//当前正在执行的command的一些信息
static void clearPendingCommand()
{
    if (sp_response != NULL) {
        at_response_free(sp_response);
    }

    sp_response = NULL;
    s_responsePrefix = NULL;
    s_smsPDU = NULL;
}


/**
 * Starts AT handler on stream "fd'
 * returns 0 on success, -1 on error
 */
 //打开AT command所使用的设备句柄，并创建readerLoop线程
int at_open(int fd, ATUnsolHandler h)
{
    int ret;
    pthread_t tid;
    pthread_attr_t attr;

    s_fd = fd;
    s_unsolHandler = h;
    s_readerClosed = 0;

    s_responsePrefix = NULL;
    s_smsPDU = NULL;
    sp_response = NULL;

    /* Android power control ioctl */
#ifdef HAVE_ANDROID_OS
#ifdef OMAP_CSMI_POWER_CONTROL
    ret = ioctl(fd, OMAP_CSMI_TTY_ENABLE_ACK);
    if(ret == 0) {
        int ack_count;
		int read_count;
        int old_flags;
        char sync_buf[256];
        old_flags = fcntl(fd, F_GETFL, 0);
        fcntl(fd, F_SETFL, old_flags | O_NONBLOCK);
        do {
            ioctl(fd, OMAP_CSMI_TTY_READ_UNACKED, &ack_count);
			read_count = 0;
            do {
                ret = read(fd, sync_buf, sizeof(sync_buf));
				if(ret > 0)
					read_count += ret;
            } while(ret > 0 || (ret < 0 && errno == EINTR));
            ioctl(fd, OMAP_CSMI_TTY_ACK, &ack_count);
         } while(ack_count > 0 || read_count > 0);
        fcntl(fd, F_SETFL, old_flags);
        s_readCount = 0;
        s_ackPowerIoctl = 1;
    }
    else
        s_ackPowerIoctl = 0;

#else // OMAP_CSMI_POWER_CONTROL
    s_ackPowerIoctl = 0;

#endif // OMAP_CSMI_POWER_CONTROL
#endif /*HAVE_ANDROID_OS*/

    pthread_attr_init (&attr);
    pthread_attr_setdetachstate(&attr, PTHREAD_CREATE_DETACHED);

    ret = pthread_create(&s_tid_reader, &attr, readerLoop, &attr);

    if (ret < 0) {
        perror ("pthread_create");
        return -1;
    }


    return 0;
}

/* FIXME is it ok to call this from the reader and the command thread? */
void at_close()
{
    if (s_fd >= 0) {
        close(s_fd);
    }
    s_fd = -1;

    pthread_mutex_lock(&s_commandmutex);

    s_readerClosed = 1;

    pthread_cond_signal(&s_commandcond);

    pthread_mutex_unlock(&s_commandmutex);

    /* the reader thread should eventually die */
}

static ATResponse * at_response_new()
{
    return (ATResponse *) calloc(1, sizeof(ATResponse));
}

void at_response_free(ATResponse *p_response)
{
    ATLine *p_line;

    if (p_response == NULL) return;

    p_line = p_response->p_intermediates;

    while (p_line != NULL) {
        ATLine *p_toFree;

        p_toFree = p_line;
        p_line = p_line->p_next;

        free(p_toFree->line);
        free(p_toFree);
    }

    free (p_response->finalResponse);
    free (p_response);
}

/**
 * The line reader places the intermediate responses in reverse order
 * here we flip them back
 */
static void reverseIntermediates(ATResponse *p_response)
{
    ATLine *pcur,*pnext;

    pcur = p_response->p_intermediates;
    p_response->p_intermediates = NULL;

    while (pcur != NULL) {
        pnext = pcur->p_next;
        pcur->p_next = p_response->p_intermediates;
        p_response->p_intermediates = pcur;
        pcur = pnext;
    }
}

/**
 * Internal send_command implementation
 * Doesn't lock or call the timeout callback
 *
 * timeoutMsec == 0 means infinite timeout
 */

static int at_send_command_full_nolock (const char *command, ATCommandType type,
                    const char *responsePrefix, const char *smspdu,
                    long long timeoutMsec, ATResponse **pp_outResponse)
{
    int err = 0;
#ifndef USE_NP
    struct timespec ts;
#endif /*USE_NP*/

    if(sp_response != NULL) {
        err = AT_ERROR_COMMAND_PENDING;
        goto error;
    }

    err = writeline (command);

    if (err < 0) {
        goto error;
    }

    s_type = type;
    s_responsePrefix = responsePrefix;
    s_smsPDU = smspdu;
    sp_response = at_response_new();

#ifndef USE_NP
    if (timeoutMsec != 0) {
        setTimespecRelative(&ts, timeoutMsec);
    }
#endif /*USE_NP*/

	/*
	一直循环等待
	
	如果timeoutMsec的值为0，那么就一直等待直到readerLoop里面读到AT Response,
	如果值不为0，就等待指定的时间
	
	*/

    while (sp_response->finalResponse == NULL && s_readerClosed == 0) {
        if (timeoutMsec != 0) {
#ifdef USE_NP
            err = pthread_cond_timeout_np(&s_commandcond, &s_commandmutex, timeoutMsec);
#else
            err = pthread_cond_timedwait(&s_commandcond, &s_commandmutex, &ts);
#endif /*USE_NP*/
        } else { 

            err = pthread_cond_wait(&s_commandcond, &s_commandmutex);
        }

        if (err == ETIMEDOUT) {
            err = AT_ERROR_TIMEOUT;
            goto error;
        }
    }

    if (pp_outResponse == NULL) {
        at_response_free(sp_response);
    } else {
        /* line reader stores intermediate responses in reverse order */
        reverseIntermediates(sp_response);
	//上面调用的人要自己调用at_response_free来释放
        *pp_outResponse = sp_response;
    }

    sp_response = NULL;

    if(s_readerClosed > 0) {
        err = AT_ERROR_CHANNEL_CLOSED;
        goto error;
    }

    err = 0;
error:
    clearPendingCommand();

    return err;
}

/**
 * Internal send_command implementation
 *
 * timeoutMsec == 0 means infinite timeout

 timeoutMsec == 0表示无限的等待
 */
static int at_send_command_full (const char *command, ATCommandType type,
                    const char *responsePrefix, const char *smspdu,
                    long long timeoutMsec, ATResponse **pp_outResponse)
{
    int err;

    if (0 != pthread_equal(s_tid_reader, pthread_self())) {
        /* cannot be called from reader thread */
        return AT_ERROR_INVALID_THREAD;
    }

    pthread_mutex_lock(&s_commandmutex);

    err = at_send_command_full_nolock(command, type,
                    responsePrefix, smspdu,
                    timeoutMsec, pp_outResponse);

    pthread_mutex_unlock(&s_commandmutex);

    if (err == AT_ERROR_TIMEOUT && s_onTimeout != NULL) {
        s_onTimeout();
    }

    return err;
}


/**
 * Issue a single normal AT command with no intermediate response expected
 *
 * "command" should not include \r
 * pp_outResponse can be NULL
 *
 * if non-NULL, the resulting ATResponse * must be eventually freed with
 * at_response_free
 */
int at_send_command (const char *command, ATResponse **pp_outResponse)
{
    int err;

    err = at_send_command_full (command, NO_RESULT, NULL,
                                    NULL, 0, pp_outResponse);

    return err;
}

/*
第一个参数是AT command
第二个参数是该AT command的AT response的前缀
第三个是AT response的值


*/
int at_send_command_singleline (const char *command,
                                const char *responsePrefix,
                                 ATResponse **pp_outResponse)
{
    int err;

    err = at_send_command_full (command, SINGLELINE, responsePrefix,
                                    NULL, 0, pp_outResponse);

  //成功的command必须有中间response
    if (err == 0 && pp_outResponse != NULL
        && (*pp_outResponse)->success > 0
        && (*pp_outResponse)->p_intermediates == NULL
    ) {
        /* successful command must have an intermediate response */
        at_response_free(*pp_outResponse);
        *pp_outResponse = NULL;
        return AT_ERROR_INVALID_RESPONSE;
    }

    return err;
}


int at_send_command_numeric (const char *command,
                                 ATResponse **pp_outResponse)
{
    int err;

    err = at_send_command_full (command, NUMERIC, NULL,
                                    NULL, 0, pp_outResponse);

    if (err == 0 && pp_outResponse != NULL
        && (*pp_outResponse)->success > 0
        && (*pp_outResponse)->p_intermediates == NULL
    ) {
        /* successful command must have an intermediate response */
        at_response_free(*pp_outResponse);
        *pp_outResponse = NULL;
        return AT_ERROR_INVALID_RESPONSE;
    }

    return err;
}


int at_send_command_sms (const char *command,
                                const char *pdu,
                                const char *responsePrefix,
                                 ATResponse **pp_outResponse)
{
    int err;

    err = at_send_command_full (command, SINGLELINE, responsePrefix,
                                    pdu, 0, pp_outResponse);

    if (err == 0 && pp_outResponse != NULL
        && (*pp_outResponse)->success > 0
        && (*pp_outResponse)->p_intermediates == NULL
    ) {
        /* successful command must have an intermediate response */
        at_response_free(*pp_outResponse);
        *pp_outResponse = NULL;
        return AT_ERROR_INVALID_RESPONSE;
    }

    return err;
}


int at_send_command_multiline (const char *command,
                                const char *responsePrefix,
                                 ATResponse **pp_outResponse)
{
    int err;

    err = at_send_command_full (command, MULTILINE, responsePrefix,
                                    NULL, 0, pp_outResponse);

    return err;
}


/** This callback is invoked on the command thread */
void at_set_on_timeout(void (*onTimeout)(void))
{
    s_onTimeout = onTimeout;
}

/**
 *  This callback is invoked on the reader thread (like ATUnsolHandler)
 *  when the input stream closes before you call at_close
 *  (not when you call at_close())
 *  You should still call at_close()
 */

void at_set_on_reader_closed(void (*onClose)(void))
{
    s_onReaderClosed = onClose;
}


/**
 * Periodically issue an AT command and wait for a response.
 * Used to ensure channel has start up and is active
 */
/*握手，保证channel已经启动并且是alive的*/
int at_handshake()
{
    int i;
    int err = 0;

    if (0 != pthread_equal(s_tid_reader, pthread_self())) {
        /* cannot be called from reader thread */
        return AT_ERROR_INVALID_THREAD;
    }

    pthread_mutex_lock(&s_commandmutex);

    for (i = 0 ; i < HANDSHAKE_RETRY_COUNT ; i++) {
        /* some stacks start with verbose off */
        err = at_send_command_full_nolock ("ATE0Q0V1", NO_RESULT,
                    NULL, NULL, HANDSHAKE_TIMEOUT_MSEC, NULL);

        if (err == 0) {
            break;
        }
    }

    if (err == 0) {
        /* pause for a bit to let the input buffer drain any unmatched OK's
           (they will appear as extraneous unsolicited responses) */

        sleepMsec(HANDSHAKE_TIMEOUT_MSEC);
    }

    pthread_mutex_unlock(&s_commandmutex);

    return err;
}

/**
 * Returns error code from response
 * Assumes AT+CMEE=1 (numeric) mode
 */
AT_CME_Error at_get_cme_error(const ATResponse *p_response)
{
    int ret;
    int err;
    char *p_cur;

    if (p_response->success > 0) {
        return CME_SUCCESS;
    }

    if (p_response->finalResponse == NULL
        || !strStartsWith(p_response->finalResponse, "+CME ERROR:")
    ) {
        return CME_ERROR_NON_CME;
    }

    p_cur = p_response->finalResponse;
    err = at_tok_start(&p_cur);

    if (err < 0) {
        return CME_ERROR_NON_CME;
    }

    err = at_tok_nextint(&p_cur, &ret);

    if (err < 0) {
        return CME_ERROR_NON_CME;
    }

    return (AT_CME_Error) ret;
}