Skip to content

Latest commit

 

History

History
95 lines (64 loc) · 5.07 KB

proxy_protocol.md

File metadata and controls

95 lines (64 loc) · 5.07 KB
Raw

elaphureLink Proxy Protocol

The elaphureLink proxy protocol follows a server/client architecture. The server exports the DAP device and client imports it.

The elaphureLink proxy protocol is compliant with the CMSIS-DAP protocol. This means that any data transmitted in the elaphureLink proxy is a valid CMSIS-DAP command.

For more information about CMSIS-DAP, see CMSIS-DAP command

There are two main phases in the elaphureLink Proxy Protocol, the handshake phase and the data transfer phase. All phases will be done in the same TCP/IP connection.

Due to the limitations that exist in the CMSIS-DAP protocol, all packet transmissions should be transmitted as a complete packet at the low level transport layer.

Handshake phase

The client may ask the server if it supports the elaphureLink proxy protocol. To do this, the client opens a tcp/ip connection and sends a REQ_HANDSHAKE packet. Once the server supports the elaphureLink proxy protocol and receives a packet from the client, it will respond with RES_HANDSHAKE packet.

elaphureLink Proxy                                      DAP host
     "client"                                           "server"
 (imports DAP device)                             (exports DAP device)
         |                                                 |
         |                  REQ_HANDSHAKE                  |
         | ----------------------------------------------> |
         |                                                 |
         |                  RES_HANDSHAKE                  |
         | <---------------------------------------------- |
         |                                                 |

When the client receives RES_HANDSHAKE, it can decide by itself whether to proceed with the import of DAP devices. If the import of DAP devices is performed, then the data transfer phase can be started immediately, or it can be performed later. Otherwise, the client should disconnect the established TCP/IP connection.

REQ_HANDSHAKE and RES_HANDSHAKE are also valid CMSIS-DAP commands. More specifically, they are CMSIS-DAP Vendor Command, and such a convention simplifies the server implementation.

Data transfer phase

During the data transmission phase, the CMSIS-DAP command is transmitted as is.

One or more packets can be transmitted in a single packet transmission. elaphureLink may prefer to merge multiple CMSIS-DAP commands and transmit them in the same packet. To this end, elaphureLink make the following conventions:

  1. Use the DAP_ExecuteCommands to transfer multiple CMSIS-DAP commands in a single packet.
  2. For client, if a CMSIS-DAP command with an unpredictable response length needs to be sent, the command is placed last and it can only appear once.

For DAP_ExecuteCommands, see DAP_ExecuteCommands command

The advantage of this is that for DAP host, few or no modifications are required to meet the requirements of the protocol.

elaphureLink Proxy                                      DAP host
     "client"                                           "server"
 (imports DAP device)                             (exports DAP device)
         |                                                 |
         |               REQ_CMSIS_DAP_COMMAND             |
         | ----------------------------------------------> |
         |                                                 |
         |               RES_CMSIS_DAP_COMMAND             |
         | <---------------------------------------------- |
         |                       .                         |
         |                       .                         |
         |                       .                         |
         |               REQ_CMSIS_DAP_COMMAND             |
         | ----------------------------------------------> |
         |                                                 |
         |               RES_CMSIS_DAP_COMMAND             |
         | <---------------------------------------------- |
         |                                                 |

Packet Reference

The fields are in network (big endian) byte order meaning that the most significant byte (MSB) is stored at the lowest address.

REQ_HANDSHAKE

Offset Length Value Description
0 4 0x8a656c70 elaphureLink Proxy Protocol Identifier
4 4 0x00000000 Command code: handshake
8 4 elaphureLink Proxy Version

RES_HANDSHAKE

Offset Length Value Description
0 4 0x8a656c70 elaphureLink Proxy Protocol Identifier
4 4 0x00000000 Command code: handshake
8 4 elaphureLink DAP Firmware Version