RIME协议栈解读

news2024/7/6 19:17:48

// 新坑–contiki

rime简介

rime类似于TCP/IP协议栈，属于分层结构。图片来自Adam Dunkels本人的rime论文介绍。
rime

abc为anonymous broadcast，匿名广播。即将数据包通过无线射频驱动(radio driver)发出去，接收来自无线射频驱动所有的包并交给上层。
ibc为identified sender best-effort broadcast，将下层传来的数据包添加一个发送者身份头部——使用数组形式。
uc为unicast abstraction，将上层的数据包添加一个接收者头部。
suc为Stubborn transmission。可靠通信就由这两层实现：Stubborn transmission、Reliable transmission。
Stubborn transmission层在给定的时间间隔、最大重发次数后不断地重发数据包。
Reliable communication层主要实现确认和序列功能，确认来自Stubborn transmission层的数据。
Bulk transfer为块传输层。该层有实现了单跳单播、单跳广播、多跳的包。

两个节点之间的通信图：
nodes

数据包格式

数据包格式如下：
packetbuf

数据包头部header

rime协议为了解决不同网络协议头部不兼容的问题，设计出了无头部数据包。
见packetbuf.h，该文件定义了数据包头部的基本格式。

struct packetbuf_attrlist
{
  uint8_t type;
  uint8_t len;
};

数据包数据data

Rime缓冲区存放数据包属性（header）和应用数据（data）。大小是这两部分的和，Rime缓冲区由静态全局变量packetbuf定义。

static uint16_t packetbuf_aligned[(PACKETBUF_SIZE + PACKETBUF_HDR_SIZE)/2+1];  // PACKETBUF_SIZE默认大小是128字节
static uint8_t *packetbuf = (uint8_t*)packetbuf_aligned;      				   // 确保了即使在16位边界 (如MSP430) 也能对齐

数据包操作API

源自packetbuf.h，用于操作数据缓存

// Clear and reset the packetbuf
void packetbuf_clear(void);
// Get a pointer to the data in the packetbuf
void *packetbuf_dataptr(void);
// Get a pointer to the header in the packetbuf, for outbound packets
void *packetbuf_hdrptr(void);
// Get the length of the header in the packetbuf
uint8_t packetbuf_hdrlen(void);
// Get the length of the data in the packetbuf
uint16_t packetbuf_datalen(void);
// Get the total length of the header and data in the packetbuf
uint16_t packetbuf_totlen(void);
// Get the total length of the remaining space in the packetbuf
uint16_t packetbuf_remaininglen(void);
// Set the length of the data in the packetbuf
void packetbuf_set_datalen(uint16_t len);
// Compact the packetbuf
void packetbuf_compact(void);
// Copy from external data into the packetbuf
int packetbuf_copyfrom(const void *from, uint16_t len);
// Copy the entire packetbuf to an external buffer
int packetbuf_copyto(void *to);
// Extend the header of the packetbuf, for outbound packets
int packetbuf_hdralloc(int size);
// Reduce the header in the packetbuf, for incoming packets
int packetbuf_hdrreduce(int size);

rucb解析

此章仅单独研究rubc单跳单播协议。

建立连接

依次调用rucb_open() --> runicast_open() --> stunicast_open() --> unicast_open() --> broadcast_open() --> abc_open() --> channel_open()

发送数据包

struct rucb_conn {                     // rucb_conn为rubc协议的存储连接信息的结构体
  struct runicast_conn c;              // 链式结构
  const struct rucb_callbacks *u;      // 回调函数，每一层的连接信息结构体都有对应的callback
  linkaddr_t receiver, sender;         // 接收器、发送器
  uint16_t chunk;					   // 通道序号，只有0和1两个值。当前为0，next为1
  uint8_t last_seqno;
  int last_size;
};

int rucb_send(struct rucb_conn *c, const linkaddr_t *receiver)
{
  c->chunk = 0;  					                 // chunk置为0，表示当前正在运行
  read_data(c);										 // 调用read_chunk()
  linkaddr_copy(&c->receiver, receiver);             // 调用memcpy(dest, src)，完善c属性
  linkaddr_copy(&c->sender, &linkaddr_node_addr);
  runicast_send(&c->c, receiver, MAX_TRANSMISSIONS);  // 调用runicast的send方法
  return 0;
}

int runicast_send(struct runicast_conn *c, const linkaddr_t *receiver, uint8_t max_retransmissions)
{
	...
	packetbuf_set_attr(PACKETBUF_ATTR_RELIABLE, 1);	// packetbuf_attrs[PACKETBUF_ATTR_RELIABLE].val = 1;					
  	packetbuf_set_attr(PACKETBUF_ATTR_PACKET_TYPE, PACKETBUF_ATTR_PACKET_TYPE_DATA);
  	packetbuf_set_attr(PACKETBUF_ATTR_PACKET_ID, c->sndnxt);
  	packetbuf_set_attr(PACKETBUF_ATTR_MAX_MAC_TRANSMISSIONS, 3);
  	...
  	stunicast_send_stubborn(&c->c, receiver, REXMIT_TIME);
  	...
}

后面同理，一边向下层传递，一边设置头数组。最后由链路层调用send()方法发送
stunicast_send_stubborn() --> unicast_send() --> broadcast_send() --> abc_send() --> rime_output() --> NETSTACK_LLSEC.send()

最后完整的数据包头数组格式如下：
在这里插入图片描述
头数组type类型为enum：

enum
{
  PACKETBUF_ATTR_NONE,
  /* Scope 0 attributes: used only on the local node. */
  PACKETBUF_ATTR_CHANNEL,
  PACKETBUF_ATTR_NETWORK_ID,
  PACKETBUF_ATTR_LINK_QUALITY,
  PACKETBUF_ATTR_RSSI,
  PACKETBUF_ATTR_TIMESTAMP,
  PACKETBUF_ATTR_RADIO_TXPOWER,
  PACKETBUF_ATTR_LISTEN_TIME,
  PACKETBUF_ATTR_TRANSMIT_TIME,
  PACKETBUF_ATTR_MAX_MAC_TRANSMISSIONS,
  PACKETBUF_ATTR_MAC_SEQNO,
  PACKETBUF_ATTR_MAC_ACK,
  /* Scope 1 attributes: used between two neighbors only. */
  PACKETBUF_ATTR_RELIABLE,
  PACKETBUF_ATTR_PACKET_ID,
  PACKETBUF_ATTR_PACKET_TYPE,
  PACKETBUF_ATTR_REXMIT,
  PACKETBUF_ATTR_MAX_REXMIT,
  PACKETBUF_ATTR_NUM_REXMIT,
  PACKETBUF_ATTR_PENDING,
  /* Scope 2 attributes: used between end-to-end nodes. */
  PACKETBUF_ATTR_HOPS,
  PACKETBUF_ATTR_TTL,
  PACKETBUF_ATTR_EPACKET_ID,
  PACKETBUF_ATTR_EPACKET_TYPE,
  PACKETBUF_ATTR_ERELIABLE,
  /* These must be last */
  PACKETBUF_ADDR_SENDER,
  PACKETBUF_ADDR_RECEIVER,
  PACKETBUF_ADDR_ESENDER,
  PACKETBUF_ADDR_ERECEIVER,

  PACKETBUF_ATTR_MAX
};

接收数据包

相同方法，不做分析

callback

就像在发送数据中说的，callback作为每层连接结构体conn必有的成员变量回调结构体指向上一层的回调结构体，即接收到数据总是提交给上一层处理。
例如，在runicast_callbacks结构体中，分别映射到接收recv、确认acked、超时timedout函数（位于rubc.c）

struct runicast_callbacks
{
  void(*recv)(struct runicast_conn *c, const rimeaddr_t *from, uint8_t seqno);
  void(*sent)(struct runicast_conn *c, const rimeaddr_t *to, uint8_t retransmissions);
  void(*timedout)(struct runicast_conn *c, const rimeaddr_t *to, uint8_t retransmissions);
};