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3.3

eTPU channel initialization

After the eTPU module is configured, each channel on the eTPU module can be configured.

eTPU channel initialization includes the following tasks:

1.

eTPU channel configuration registers initialization

–

Assign eTPU function to a channel

–

Setup channel priority

–

Configure interrupt/DMA/Output enable

–

Select eTPU function entry table encoding

–

Assign the function frame to a channel

2.

eTPU channel status control register initialization

–

Set up eTPU function mode

The eTPU channel assignment and the channel priority determination are a part of the host

software architecture design. They are independent of the eTPU functions implementation.

The information for the configuration is provided by the host software design.

During the channel initialization, a section of eTPU data memory is assigned to each

channel. This memory section is called the “function frame”. The function frame contains all

the function parameters and static local variables used by the eTPU function. The starting

address of the function frame is assigned to the channel at initialization. The function frame

assignment can be static or dynamic. Dynamic allocation assigns the function frame to the

channel based on the next available memory space. The availability of the eTPU data

memory depends on the number of functions that have been assigned and the number of

parameters the function is using. Dynamic allocation can reduce the eTPU data memory

consumption by minimizing unused memory ‘holes’. To allocate the function frame

dynamically, the host must know the function frame consumption by a particular eTPU

function. The eTPU_C compiler provides a macro (::ETPUram) to report the number of

parameters and static local variables used by a function at compile time (Appendix C on

page 13).

The eTPU function table entry encoding, interrupt enable, DMA enable, output enable,

output polarity, and function mode are constants specific to the eTPU function software

implementation. It is a good practice to define them only once in the eTPU code and export

the configuration information at compile time.

Once the host interface macros are added to the eTPU code (Appendix C on page 13), the

#pragma write

statements will generate a header file that contains all the eTPU function

configuration and software symbol information at compile time (Appendix E on page 17).

The header file can be included in the host interface code to resolve symbol references.

3.4

eTPU function initialization

The eTPU function initialization is the last step of the eTPU initialization process. During the

eTPU function initialization, the host is responsible for passing the parameters to the eTPU

functions and initiating the eTPU function execution by issuing a host service request. Once

the host service request for initialization is recognized, the eTPU will transition to the

initialization state.

Unlike in the host CPU, the eTPU function parameters passed from host are not placed on

the stack. Instead, memory in the function frame is allocated to accommodate every function

parameter. The host passes the eTPU function parameters by writing directly to the eTPU