pSOSystem System Calls - Read

pSOS+ System Calls as_return
as_return Returns from an asynchronous signal routine (ASR).
#include
unsigned long as_return();
Description
Target
This system call must be used by a task's ASR to exit and return to the original flow
of execution of the task. The purpose of this call is to enable the pSOS+ kernel to
restore the task to its state before the ASR. as_return() cannot be called except
from an ASR.
This call is analogous to the i_return() call, which enables an Interrupt Service
Routine (ISR) to return to the interrupted flow of execution properly.
Restoring CPU Registers
An ASR is responsible for restoring CPU registers to their previous state before
exiting via as_return(). The exact way in which this happens varies from
processor to processor. On most processors, the ASR is written in assembly
language, so you the programmer must take care to restore the registers. On
PowerPC processors, an ASR can be written in C, and the pSOS+ kernel restores the
registers. Processor-specific information on restoring registers prior to
as_return() is provided below:
68K
960
x86
On 68K processors, an ASR is responsible for saving and restoring all
CPU registers it uses, including stack pointers. The one exception to
this rule is the register D0.L, which is restored by the pSOS+ kernel. On
68K processors, an ASR can be written only in assembly language.
On 960 processors, an ASR is responsible for saving and restoring all
CPU registers it uses, including stack pointers. The one exception to
this rule is the register g0, which is restored by the pSOS+ kernel. On
960 processors, an ASR can be written only in assembly language.
On x86 processors, an ASR is responsible for saving and restoring all
CPU registers it uses, including stack pointers. The one exception to
this rule is the register EAX, which is restored by the pSOS+ kernel. On
x86 processors, an ASR can be written only in assembly language.
pSOSystem System Calls 1-7
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