AN2618

Overview

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Overview

Host interface software adds another layer of abstraction between the host CPU and eTPU.

The host interface API functions hide the complexity of the interaction between the host

CPU and eTPU, providing a simple interface for host applications. Ideally, every eTPU

function shall have one or more host interface API functions.

The interface software between host and eTPU facilitates three major tasks:

1.

eTPU hardware initialization – configure eTPU peripheral hardware

2.

eTPU function initialization – pass initial parameters and initiate function execution

3.

eTPU function run time interactive control – update function parameters and handle

handshaking

Once the eTPU peripheral and eTPU functions are initialized, each eTPU function can start

to execute with initial function parameters. The host interface API functions need to be

provided for interactive control (i.e. parameters updating and control mode changing etc.).

To update the parameter or change control mode, the host is responsible for passing

updated parameters to the eTPU functions, and then informing the eTPU that the function

parameters have changed. If a coherent change of function parameters is required, the logic

has to be built in the eTPU functions to ensure the coherency. For some eTPU functions, the

interaction between host and eTPU is an essential part of the operation. In both host and

eTPU software, the logic is needed to handle the handshaking between host and eTPU. The

interaction between the eTPU and host can be encapsulated in the host interface API

functions.

The host code and eTPU code are compiled by different compilers. The host compiler is

normally used to build a single code image for both host and eTPU. In order to build eTPU

code and host code together, the eTPU software building information (i.e. eTPU code

image) has to be exported to the host compiler. The symbol information has to be exported

from the eTPU compiler to the host compiler as well. For the Byte Craft eTPU compiler, the

mechanism is implemented as a set of host interface macros. In the eTPU code, these

macros are inserted to generate proper executable and symbol information for the host

compiler.

The host interface design process is illustrated in the eTPU PWM driver examples in the

Appendices.