ST20-C1 datasheet(45/205 Pages) STMICROELECTRONICS

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4 Using ST20-C1 instructions

where the label

ENDIF: is at the end of the code for the if construct.

The compilation of a while loop is shown by the following example.

while (

E){

}

This compiles to:

E; cj ENDWHILE

P; timeslice; j L

ENDWHILE:

Note that this loop includes a

timeslice instruction. This causes the current process to

be descheduled if a timeslice is due and timeslicing is enabled. The presence of this

ensures that the process cannot occupy the CPU for too long provided timeslicing is

enabled. It is good practice for multi-tasking programs to include a

timeslice instruction

in every loop. Timeslicing is described in section 7.4. Single task programs do not

need to timeslice, but should have timeslicing disabled, so the

timeslice instruction

has no effect.

A repeat .. until loop is shown by the following example.

repeat {

} until

This compiles to:

E; eqc 0; cj END

P; timeslice; j L

END:

4.6.5

Ordering instructions

Two instructions are provided to select the smaller of two values. If Breg is smaller

than Areg as a signed integer,

order will swap Areg and Breg; otherwise order will

have no effect. This can be used to find the minim um of two signed variables:

ldl a; ldl b; order;

stl minimum; stl maximum

Similarly

orderu can be used to find the minimum or maximum of two unsigned values

4.7

Evaluation of boolean expressions

This section describes the operations using the logical

true and false values, as used

with the conditional jump

cj. Conditional behavior and comparisons are described in

section 4.6. Bitwise boolean operations are described in section 4.8. General issues

concerning expression evaluation are discussed in section 4.3.

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