AN3350 datasheet(63/185 Pages) STMICROELECTRONICS

63 / 185 page

AN3350

Working with the assembler

Doc ID 018512 Rev 2

63/185

Directives begin with the decimal character (.) and feature syntax similar to that of

instructions. A label preceding a directive is not considered part of the directive.

10.4.1

Memory spaces and sections

A section is a continuous memory block. Sections are basic logical units you can use to

organize code and data into groups, controlling size, content and starting point of each

group or section. At loading time, the content of the user-defined logical sections and

possible system-added extra sections are loaded into actual memory segments.

eTPU architecture has two types of memory space and each loadable section belongs to

exactly one of them. Defining code or data from outside a section is not allowed:

●

Code Space (denoted c) is intended for instruction storage. It features a 32-bit access

width, within which the 32 bits instructions are stored (aligned to 4 bytes addresses).

The address range for this space is 24 bits.

●

Data Space (denoted d) is used to load and store data. It also has an access width of 8

bits and an address range of 24 bits.

Note:

Debug and other unloadable sections do not relate to a physical memory space and have an

imaginary access width of 8 bits.

Use of the term address should be understood as a shortcut to the full address. The latter is

space:addr

in which addr is the integer location for the word to be found in the space

memory space. For example: 'nop at c:57' is the instruction NOP located at address 57

in the code memory space. In most cases, however, there is no need for a space reference

as it is uniquely inferred by the instruction. The only time space names are explicitly

mentioned is when a memory space is assigned to a section using the .org address or

the .section sec directive.

Sections can be either relative or absolute. Relative sections are declared by name and

space (using the .section sec directive) and are assigned an address during the linking

stage. Section names are symbols. When the memory space is omitted, the section is

considered a code section. Some predefined special sections (as well as absolute sections,

defined below) used by the Elf and Dwarf2 binary formats have names that begin with the

dot character ('.'). As an exception, these sections might also be pre-assigned to a space

(for example, the .data section will be loaded as data).

Absolute sections are declared using the.org address directive. They are nameless - the

name is automatically built from space and address characteristics - but must have a known

memory space and address. When the memory space is omitted it is assumed to be the

code space. .org sections can not be repeated, however - other address overlaps

between absolute sections will be checked and flagged by the linker tool.

Upon meeting a relative section directive, the following content is added (without alignment)

at the end of the section portion generated so far.

.org

sections, on the other hand, can not be repeated. The .previous directive can be

used to switch back and forth between any two sections. Address overlaps between all

sections will be checked and flagged by the linker tool.

10.4.2

Data storage

Each code statement stores 4 bytes into memory. Data can be stored in different sizes and

ways.

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