13.6.1. Overview of the Angel communications layers

Figure 13.12 shows a conceptual model of the communication layers for Angel. In practice, some layers might be combined.

Figure 13.12. Communications layers for Angel

The channels layer includes:


The Angel Debug Protocol channel. This consists of the Host ADP channel (HADP) and Target ADP channel (TADP).


The boot channel.


The Thumb debug communications channel.


C library support.

At the top level on the target, the Angel agent communicates with the debugger host, and the user application can make use of semihosting support (CLIB).

All communications for debugging (ADP, BOOT, TDCC, CLIB) require a Reliable channel between the target and the host. The Reliable communications and buffer management layer is responsible for providing reliability, retransmissions, and multiplexing/de-multiplexing for these channels. This layer must also handle buffer management, because reliability requires retransmission after errors have occurred.

The device driver layer detects and rejects bad packets but does not offer reliability itself.

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