Porting RTOS Device Drivers to Embedded Linux

Transform your wild-and-woolly legacy RTOS code into well-formed Linux device drivers.
Migrating Network Drivers

As indicated above, porting character and block device drivers to Linux is a straightforward if time-consuming activity. Porting network drivers, though, can seem much more daunting.

Remember that while Linux grew up with TCP/IP, most RTOSes had networking grafted onto them in the late 1990s. As such, legacy networking often only presents bare-bones capabilities, such as being able to handle only a single session or instance on a single port or to support only a physical interface on a single network medium. In some cases, networking architecture was generalized after the fact, as with Wind River VxWorks MUX code to allow for multiple interfaces and types of physical connection.

The bad news is that you likely have to rewrite most or all of your existing network interfaces. The good news is that re-partitioning for Linux is not hard and you have dozens of open-source network device driver examples to choose from.

Your porting task is to populate the areas at the bottom of Figure 4 with suitable packet formatting and interface code.

Figure 4. Block Diagram of Linux Network Drivers

Writing network drivers is not for beginners. Because, however, many RTOS network drivers actually were derived from existing GPL Linux interfaces, you might find the process facilitated by the code itself. Moreover, there is a large and still-growing community of integrators and consultants focused on making a business of helping embedded developers move their applications to Linux, for reasonable fees.

Conclusion

The goal of this article has been to give embedded developers some insight into both the challenges they will face and benefits they will realize from moving their entire software stack from a legacy RTOS to Linux. The span of 2,800 words or so is too brief to delve into many of the details of driver porting (driver APIs for bus interfaces, address translation and so on), but the wealth of existing open-source GPL driver code serves as both documentation and a template for your migration efforts. The guidelines presented here should help your team scope the effort involved in a port of RTOS to Linux and provide heuristics for re-partitioning code for the best native fit to embedded Linux.

As Director of Strategic Marketing and Technology Evangelist when he wrote this article, Bill focused his 17+ years of industry experience on advancing MontaVista and embedded Linux in today's dynamic pervasive computing marketplace. His background includes extensive embedded and real-time experience with expertise in OS, tools, software licensing and manufacturing.

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As the author and a few

Moshe's picture

As the author and a few commenters rightfully noted you can go the easy path by mapping all VxWorks tasks to Linux user mode processes/threads. The downside is that the performance hit can be huge (see above comment about mmap overhead).

Fortunately, it looks like now there is a solution - www.femtolinux.com allows to run user processes in kernel mode, removing the user/kernel barrier. FemtoLinux processes are pretty much identical to VxWorks tasks.

Been on both sides of this

Baumann's picture

15 years as a VxWorks developer, now doing the linux side of the game. 99% of the time, the "real driver" approach is the preferred one - you get protection, etc. (I've ported almost all of my old VxWorks drivers to Linux that way) but there is the odd case - and I'm dealing with one now, where mmap() may buy you the realtime response you need - where even the interrupts are too slow.
(porting from linux to VxWorks is the easy direction - you're going from protected to unprotected,life is easy, aside from a few calls that aren't allowed.)
My catch at the moment though - on the architecture that I'm working with, is that the mmap call is expensive - more than you might think. Each access, by the time it has rolled up and unrolled the various page tables, is appearing to take 700ns - dropping memory bandwidth to less than 14MB/Sec. And that bytes. Pun intended.
Like everything, you've got to evaluate what you're doing, and why

migration kit for linux to vxworks - availablility !!

karthik bala guru's picture

Hi all,
VxWorks-to-Linux migration kits are offered by a number of companies, including MapuSoft, LynuxWorks, MontaVista, and TimeSys.

But, y is there no such thing like,
Linux-to-VxWorks Migration Kits ????

What is the difficulty in providing such a migration kit ?
where is the problem actually ?

if there is a linux-to-vxworks migration kit available in any website or shop, do kindly let me know.

thanks and regards,
karthik bala guru

migrating a protocol from linux to vxworks - availablility !!

karthik bala guru's picture

actually, i am porting a protocol stack developed in arm-linux into vxworks.

do let me know if there is any migration kit for this.

cheeers,
karthik bala guru

How to implement mmap() in vxWorks?

Anonymous's picture

Does anybody know how to use linux mmap() like function in vxWorks?
Please info me!

hmmm

Vijaykc's picture

Why would you want mmap()in Vxworks? The entire memory space is yours..... :)
I am not quite sure why you need one the first place.

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