Embedded Software for SoC - Grupo de Mecatrônica EESC/USP

184 Chapter 14
HAL API on a processor, Proc #1. When we design a new SoC #2 shown in
Figure 14-5(b), if the new design uses the same HAL API, then, the same
SW IP can be reused without changing the code. In this case, the target
processor on the new SoC design (Proc #2) may be different from the one
(Proc #1) for which the SW IP was developed initially.
4.2 HAL standard for SoC design
As in the case of HW interface standard, HAL needs also standards to enable
easy SW reuse across industries as well as across in-house design groups. In
VSIA, a development working group (DWG) for HdS (hardware dependent
software) works to establish a standard of HAL API since September 2001 [1].
When we imagine a standard of HAL API, we may have a question: how
can such a HAL standard support various and new hardware architectures
Compared with conventional board designs, one of characteristics in SoC
design is application-specific HW architecture design. To design an optimal
HW architecture, the designer can invent any new HW architectures that an
existing, maybe, fixed HAL may not support. To support such new architectures,
a fixed standard of HAL API will not be sufficient. Instead, the standard
HAL API needs to be a generic HAL API that consists of common HAL API
functions and a design guideline to extend HAL API functions according to
new HW architectures. It will be also possible to prepare a set of common
HAL APIs suited to several application domains (e.g. a HAL API for multimedia
applications) together with the design guideline.
The guideline to develop extensible HAL API functions needs to be a
component-based construction of HAL, e.g. as in [5]. In this case, HAL
consists of components, i.e. basic functional components. Components communicate
via clear interface, e.g. C++ abstract class for the interface. To implement
the standard of HAL API, their internal implementations may depend
on HW architectures.
5. HAL ISSUES
In this section, we present the following three issues related with HAL for
SoC design: HAL modelling, application-specific and automatic HAL design.
5.1. HAL modelling
When using a HAL API in SW reuse or in concurrent HW and SW design,
the first problem that the designer encounters is how to validate the upper
layer SW with the HW architecture that may not be designed yet. Figure
14-6 shows a case where the designer wants to reuse the upper layer SW
including application SW, OS and a communication middleware, e.g. message
passing interface library. At the first step of SoC design, the designer needs