AN3350 datasheet(179/185 Pages) STMICROELECTRONICS

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AN3350

eTPU specific features

Doc ID 018512 Rev 2

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standard|alternate specification. It would also locate this entry table section in the correct

location according to the given func_num.

If (standard|alternate) is not specified, standard is applied.

If a func_num is not specified, the compiler would assign a number automatically.

23.5

Memory allocation

The special architecture of the eTPU is quite different from that of most common

architectures. The number of GPRs is small and there are a lot of restrictions using them.

There is also no indirect access to memory with an offset from a register. These

characteristics lead us to have a non standard memory allocation model.

Global addresses 0-7 are for internal compiler usage and should not be used by the

programmer.

ETPU_functions arguments and static variables are allocated in a section that reside in the

channel parameter area pointed by the CPBA field. Access to these parameters shall be

using the selected channel relative addressing mode. The arguments and static variables of

an ETPU_function may occupy up to 512 bytes on the channel relative context. The

arguments are treated as static variables and continue to live after the thread ends.

Global variables are allocated in a section that resides in address 8 by default so that

access to these variables is done using the absolute addressing mode when possible.

Spilled local variables are allocated along with the global variables and also must be

accessed using the absolute addressing mode when possible.

For eTPU2 spilled local variables are allocated in a separate section, which can be

accessed using the engine relative accessing mode.

23.6

Channel structure

Channels are represented by a C structure of type chan_struct, which is declared in the

standard header file.

Only constants must be assigned to the members. The compiler validates values specific to

each field and generates an error when required. When assigning a value to one of the

members, the compiler generates an instruction, which corresponds to a field name from

the architecture spec, and assigns this field the given constant.

Note:

There is a backward compatibility problem as some of the fields where expanded in the HW

and have an extra bit in eTPU2 so the users who used CIRC and TDL in their eTPU

application would have to check their code.

23.7

Tooth Program Register (TPR) structure

The TPR structure exposes the TPR register fields to manipulation from the C language.

This structure is declared in the standard header file.

struct tpr_struct {

int TICKS

: 10;

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