AP0100CS datasheet(51/73 Pages) ONSEMI

51 / 73 page

AP0100CS/D Rev. 6, Pub. 1/16 EN

©Semiconductor Components Industries, LLC,2016.

AP0100CS HDR: Image Signal Processor (ISP)

Host Command Interface

If the host wishes to determine the outcome of the command, it must poll the Command

completed processing the command. The contents of the Command Register indicate

the command’s result status. If the command generated response parameters, the host

can now retrieve these from the Parameters Pool.

The host must not write to the Parameters Pool, nor issue another command, until the

previous command completes. This is true even if the host does not care about the result

of the previous command. It is strongly recommended that the host tests that the door-

bell bit is clear before issuing a command.

Synchronous Command Flow

The typical ‘flow’ for synchronous commands is:

1. The host issues a ‘request’ command to perform an operation.

2. The registered command handler is invoked, validates the command parameters,

then performs the operation. The handler returns the command result status to indi-

cate the result of the operation.

3. The host retrieves the command result value, and any associated command response

parameters.

Asynchronous Command Flow

The typical ‘flow’ for asynchronous commands is:

1. The host issues a ‘request’ command to start an operation.

2. The registered command handler is invoked, validates and copies the command

parameters, then signals a separate task to perform the operation. The handler

returns the ENOERR return value to indicate the command was acceptable and is in

progress.

3. The host retrieves the command return value – if it is not ENOERR the host knows that

the command was not accepted and is not in progress.

4. Subsequently, the host issues an appropriate ‘get status’ command to both poll

whether the command has completed, and if so, retrieve any associated response

parameters.

5. The registered command handler is invoked, determines the state of the command

(via shared variables with the processing task), and returns either ‘EBUSY’ to indicate

the command is still in progress, or it returns the result status of the command.

6. The host must re-issue the ‘get status’ command until it does not receive the EBUSY

response.

Asynchronous commands exist to allow the Host to issue multiple commands to the

various subsystems without having to wait for each command to complete. This

prevents the host command interface from being blocked by a long-running command.

Therefore, each asynchronous command has a “Get Status” (or similar) command to

allow the Host to determine when the asynchronous command completes.

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