CC3220STA调用sl_WlanConnect返回值错误

CC3220SF开发板使用了demo历程tcpecho_CC3220SF，debug发现调用sl_WlanConnect连接不存在的SSID的AP，返回值为0，

void Connect(void)
{
SlWlanSecParams_t secParams = {0};
int16_t ret = 0;
secParams.Key = (signed char*)SECURITY_KEY; 
secParams.KeyLen = strlen(SECURITY_KEY);
secParams.Type = SECURITY_TYPE;
Display_printf(display, 0, 0, "Connecting to : %s.\r\n",SSID_NAME);
ret = sl_WlanConnect((signed char*)SSID_NAME, strlen(SSID_NAME), 0, &secParams, 0);
if (ret)
{
printError("Connection failed", ret);
}
}

请问这是什么原因