Low Level Controller
6
ISAC®-S Low Level Controller
The following paragraphs outline the functionality and structure of a software driver example
for the ISAC-S. This example is based on the Siemens Low Level Controllers (LLC’s) for Basic
Access IC which are available in C source code. The ISAC-S software driver will be also
referred to as LLC or ISAC-S LLC.
It should be noted that the ISAC-S LLC does not access the complete palette of device funtions
but rather a subset of them. For example not all message transfer modes are supported.
Please refer to paragraph ’Architecture and Functions’ for a more detailed description.
The ISAC-S LLC presented here has been successfully tested in the Siemens ISDN PC
development system. Correct operation with a higher layer software has been verified by using
the Siemens ISDN Software Development and Evaluation System (SIDES) and the Siemens
ISDN Operational Software (IOS).
6.1
Architecture and Functions
The ISAC-S LLC may be divided into two major parts, one for Layer 1 control, the ’SBC part’
and one for directing the HDLC controller operations, the ’ICC part’. The naming conventions
’SBC part’ and ’ICC part’ have been introduced because the Low Level Controllers (LLC’s) for
Basic Access ICs use the same code to control either an ISAC-S or and ICC - SBC(X)
combination.
The ISAC-S LLC consists of driver functions and interrupt server. The driver functions are
implemented as a set of C functions which are responsible for interpreting hardware related
commands from the higher layers and carrying out the appropriate actions at the hardware
level. Driven by hardware interrupts, the interrupt server analyses the hardware event and
informs the higher software layers of that event.
It should be noted that this implementation has attempted to remove as many protocol specific
functions as possible from the LLC and to locate them instead in the higher layer protocol itself.
This has the advantage of making the LLC- more general and less likely to be in need of re-
programming for different protocols.
Semiconductor Group
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