Sahara Protocol
The protocol minimizes packet processing by relying on the physical transport
layer to provide reliable transfer of data. No framing, HDLC (High-level Data
Link Control) encoding, or CRC (Cyclic Redundancy Check) is applied to the
packets at the protocol level. Each command packet type has a well-defined
structure which minimally contains a command ID and packet length. Using this
information, the length of each command packet can be validated by comparing the
length of the command packet received to either of two values:
1. The expected packet length for the given command ID
2. The length field contained in the packet itself
Sahara can easily be extended to support command packet validation by adding a
CRC field to the end of each packet. Data packets can also be validated for data
integrity using various authentication methods; however, this is beyond the
scope of the protocol.
Synchronous communication
The protocol assumes that all communication between the host and the target is
completely synchronous. Each command packet sent from the target to the host is
acknowledged with a command or data packet sent from the host back to the
target. Similarly, each command packet sent from the host to the target is
acknowledged with a command or data packet.
Although the link between the host and the target is expected to be reliable, if
an error occurs during the transmission of a command packet from the host to the
target, and as a result the target receives an erroneous packet, then the target
will send the host an error response and exit gracefully.
Timer mechanisms can be implemented on both the host and the target to support
the retransmission of packets in case of transmission failures. However, the
implementation of such mechanisms is outside the scope of the protocol – it
specifies only what happens when unexpected or erroneous packets are received on
the target side.
Extensibility The protocol defines a fixed set of command structures and packet
flows. However, it can easily be extended to support additional command
structures and state transitions (as described later in this document).
The 3 Sahara protocol defines two types of packets:
1. Command packets
2. Data packets
Code:
Command Packet:
+------------------+-----------------+------------+------------------+
| COMMAND LENGTH | PACKET LENGTH | OPTIONAL | OPTIONAL |
+------------------+-----------------+------------+------------------+
Data Packet:
+--------------------------------------------------------------------+
| RAW DATA (arbitrary number of bytes) |
The Sahara Commands:
Code:
-----------------------------------------------------------
ID Command Description
-----------------------------------------------------------
0x00 - Invalid
0x01 Hello Initialize connection and protocol
0x02 Hello Response Acknowledge connection/protocol, mode of operation
0x03 Read Data Read specified number of bytes from host
0x04 End of Image Transfer image transfer end / target transfer failure
0x05 Done Acknowledgement: image transfer is complete
0x06 Done Response Target is exiting protocol
0x07 Reset Instruct target to perform a reset
0x08 Reset Response Indicate to host that target is about to reset
0x09 Memory Debug Indicate to host: target debug mode & ready to transfer memory content
0x0A Memory Read Read number of bytes, starting from a specified address
0x0B Command Ready Indicate to host: target ready to receive client commands
0x0C Command Switch Mode [1]
0x0D Command Execute Indicate to host: to execute a given client command
0x0E Command Execute Response Indicate to host: target command execution status
0x0F Command Execute Data Indicate to target that host is ready to receive (more) data
all - Invalid
-----------------------------------------------------------
0x0-0x8 Protocol Version 1.0 and above
0x9-0xA Protocol Version 2.0 and above
0xB-0xF Protocol Version 2.1 and above
-----------------------------------------------------------
[1] Indicate to target to switch modes:
- Image Transfer Pending mode
- Image Transfer Complete mode
- Memory Debug mode
- Command mode
- 上一篇：
- 下一篇： 安卓图形锁文件分析
支付宝
微信
呃 本文暂时没人评论 来添加一个吧