Overview
本文基於DA1458x SDK 5.0.4。
Battery Service 以下簡稱BAS or BASS。BASS的代碼主要有以下兩個組C文件組成
另，BASS是依賴於APP_TASK任務來調度管理的。具體框架如下圖（摘自Dialog官方文檔）
Full BAS Database Description （BAS Database 分析）
BASS的Database的變量名爲 bas_att_db,由以下5個成員組成
| No. | Name | Description |
|---|---|---|
| 1 | BAS_IDX_SVC | Battery Service Declaration |
| 2 | BAS_IDX_BATT_LVL_CHAR | Battery Level Characteristic Declaration |
| 3 | BAS_IDX_BATT_LVL_VAL | Battery Level Characteristic Value |
| 4 | BAS_IDX_BATT_LVL_NTF_CFG | Battery Level Characteristic - Client Characteristic Configuration Descriptor |
| 5 | BAS_IDX_BATT_LVL_PRES_FMT | Battery Level Characteristic - Characteristic Presentation Format Descriptor |
這個變量非常重要，本文我們就圍繞着它來一步步來分析。
bas_att_db結構體數組索引
首先這是一個結構體數組的索引，該索引採取的是枚舉類型，方便閱讀和理解。
/// Battery Service Attributes Indexes
enum
{
BAS_IDX_SVC,
BAS_IDX_BATT_LVL_CHAR,
BAS_IDX_BATT_LVL_VAL,
BAS_IDX_BATT_LVL_NTF_CFG,
BAS_IDX_BATT_LVL_PRES_FMT,
BAS_IDX_NB,
};接下來我們看下attm_desc這個結構體的定義
struct attm_desc 結構體的定義
這個結構體的定義如下
/// Attribute description (used to create database)
struct attm_desc
{
/// Element UUID
uint16_t uuid;
/// Attribute permission
uint16_t perm;
/// Maximum length of the element
att_size_t max_length;
/// Current length of the element
att_size_t length;
/// Element value array
uint8_t* value;
};我們可以看到，第一個成員是16位UUID，用來記錄這個Attribute（屬性）的UUID；
第二個成員是Attribute permission（屬性權限）；
第三個成員是Maximum length of the element（元素的最大長度）；
第四個成員是Current length of the element（當前元素的長處）；
第五個成員是Element Value array（元素數組）。
uuid和perm爲16bit無符號整型變量，value爲uint8_t數組指針，att_size_t類型其實uint16_t
/// Attribute length type
typedef uint16_t att_size_t;bas_att_db定義
定義如下（bass.c文件中）
/*
* BAS ATTRIBUTES DEFINITION
****************************************************************************************
*/
/// Full BAS Database Description - Used to add attributes into the database
const struct attm_desc bas_att_db[BAS_IDX_NB] =
{
// Battery Service Declaration
[BAS_IDX_SVC] = {ATT_DECL_PRIMARY_SERVICE, PERM(RD, ENABLE), sizeof(bas_svc),
sizeof(bas_svc), (uint8_t *)&bas_svc},
// Battery Level Characteristic Declaration
[BAS_IDX_BATT_LVL_CHAR] = {ATT_DECL_CHARACTERISTIC, PERM(RD, ENABLE), sizeof(bas_batt_level_char),
sizeof(bas_batt_level_char), (uint8_t *)&bas_batt_level_char},
// Battery Level Characteristic Value
[BAS_IDX_BATT_LVL_VAL] = {ATT_CHAR_BATTERY_LEVEL, PERM(RD, ENABLE), sizeof(uint8_t),
0, NULL},
// Battery Level Characteristic - Client Characteristic Configuration Descriptor
[BAS_IDX_BATT_LVL_NTF_CFG] = {ATT_DESC_CLIENT_CHAR_CFG, PERM(RD, ENABLE)|PERM(WR, ENABLE), sizeof(uint16_t),
0, NULL},
// Battery Level Characteristic - Characteristic Presentation Format Descriptor
[BAS_IDX_BATT_LVL_PRES_FMT] = {ATT_DESC_CHAR_PRES_FORMAT, PERM(RD, ENABLE), sizeof(struct prf_char_pres_fmt),
0, NULL},
};由上述定義我們來一個個分析bas_att_db的五個成員變量。
[BAS_IDX_SVC]
首先是[BAS_IDX_SVC]成員變量。
BAS_IDX_SVC的value是bas_svc 變量，具體如下：
const att_svc_desc_t bas_svc = ATT_SVC_BATTERY_SERVICE;我們可以看到bas_svc 被賦值爲一個枚舉類型變量，具體值爲0x180F。
類似的還有ATT_SVC_GENERIC_ACCESS、ATT_SVC_GENERIC_ATTRIBUTE、ATT_SVC_DEVICE_INFO、ATT_SVC_HID等。
具體定義如下：
/// Common 16-bit Universal Unique Identifier
enum {
ATT_INVALID_UUID = 0,
/*----------------- SERVICES ---------------------*/
/// Generic Access Profile
ATT_SVC_GENERIC_ACCESS = 0x1800,
/// Attribute Profile
ATT_SVC_GENERIC_ATTRIBUTE,
...
/// Device Information Service
ATT_SVC_DEVICE_INFO = 0x180A,
...
/// Battery Service
ATT_SVC_BATTERY_SERVICE,
/// Blood Pressure Service
ATT_SVC_BLOOD_PRESSURE = 0x1810,
/// Alert Notification Service
ATT_SVC_ALERT_NTF = 0x1811,
/// HID Service
ATT_SVC_HID = 0x1812,
...
}
[BAS_IDX_BATT_LVL_CHAR]
關於BAS_IDX_BATT_LVL_CHAR成員，它的value比較特殊，是att_char_desc結構體變量強轉爲（uint8_t *）。該變量定義如下：
/// Battery Level characteristic
const struct att_char_desc bas_batt_level_char = ATT_CHAR(ATT_CHAR_PROP_RD, 0, ATT_CHAR_BATTERY_LEVEL);struct att_char_desc定義如下：
/// Characteristic Value Descriptor
struct att_char_desc
{
/// properties
uint8_t prop;//屬性
/// attribute handle
uint8_t attr_hdl[ATT_HANDLE_LEN];//句柄索引
/// attribute type
uint8_t attr_type[ATT_UUID_16_LEN];//UUID值
};定義bas_batt_level_char變量時，使用ATT_CHAR宏函數填充結構體，原型如下
/// macro to fill an attribute characteristic
#define ATT_CHAR(prop, handle, type) {(prop), \
{(uint8_t)((handle)), (uint8_t)((handle) >> 8)}, \
{(uint8_t)((type)), (uint8_t)((type) >> 8)} };[BAS_IDX_BATT_LVL_VAL]、[BAS_IDX_BATT_LVL_NTF_CFG]、[BAS_IDX_BATT_LVL_PRES_FMT]
這個三個變量都沒填充value值
小結
| 成員 | 定義 | 描述 |
|---|---|---|
| [BAS_IDX_SVC] | {ATT_DECL_PRIMARY_SERVICE,PERM(RD, ENABLE),sizeof(bas_svc),sizeof(bas_svc),(uint8_t *)&bas_svc} | Battery Service Declaration |
| [BAS_IDX_BATT_LVL_CHAR] | {ATT_DECL_CHARACTERISTIC, PERM(RD, ENABLE), sizeof(bas_batt_level_char),sizeof(bas_batt_level_char), (uint8_t *)&bas_batt_level_char} | Battery Level Characteristic Declaration |
| [BAS_IDX_BATT_LVL_VAL] | {ATT_CHAR_BATTERY_LEVEL, PERM(RD, ENABLE), sizeof(uint8_t),0, NULL} | Battery Level Characteristic Value |
| [BAS_IDX_BATT_LVL_NTF_CFG] | {ATT_DESC_CLIENT_CHAR_CFG,PERM(RD, ENABLE)|PERM(WR, ENABLE),sizeof(uint16_t),0, NULL} | Battery Level Characteristic - Client Characteristic Configuration Descriptor |
| [BAS_IDX_BATT_LVL_PRES_FMT] | {ATT_DESC_CHAR_PRES_FORMAT, PERM(RD, ENABLE), sizeof(struct prf_char_pres_fmt),0, NULL} | Battery Level Characteristic - Characteristic Presentation Format Descriptor |
Database類型總結
| UUID | 類型 | 值 |
|---|---|---|
| ATT_DECL_PRIMARY_SERVICE | DECLARATIONS | 0x2800 |
| ATT_DECL_CHARACTERISTIC | DECLARATIONS | 0x2803 |
| ATT_CHAR_BATTERY_LEVEL | CHARACTERISTICS | 0x2A19 |
| ATT_DESC_CLIENT_CHAR_CFG | DESCRIPTORS | 0x2902 |
| ATT_DESC_CHAR_PRES_FORMAT | DESCRIPTORS | 0x2904 |