what is physicial contious share memory?

QNX Newsgroups (Archives) qdn.public.qnxrtp.newuser
1

Now I am programming with multi-processes to share the common data.
So I use share memory.
In the function —shm_ctl(),there are a flag SHMCTL_PHYS|SHMCTL_ANON .it
says that"
The combination SHMCTL_ANON | SHMCTL_PHYS indicates that you want
physically contiguous RAM".
1.What is physically contiguous RAM? Where is it use? I don’t understand it
clearly.
2.Must I use SHMCTL_PHYS|SHMCTL_ANON in creating share common data?

2

zhz_zhang <zhz_zhang26@sina.com> wrote:

Now I am programming with multi-processes to share the common data.
So I use share memory.
In the function —shm_ctl(),there are a flag SHMCTL_PHYS|SHMCTL_ANON .it
says that"
The combination SHMCTL_ANON | SHMCTL_PHYS indicates that you want
physically contiguous RAM".
1.What is physically contiguous RAM? Where is it use? I don’t understand it
clearly.

Some hardware drivers must allocatate physically contiguous memory
because the hardware it controls require it (from example DMA
controllers).

2.Must I use SHMCTL_PHYS|SHMCTL_ANON in creating share common data?

No. Read the online docs for shm_open() – it has an example showing
how to do this.

http://www.qnx.com/developer/docs/momentics_nc_docs/neutrino/lib_ref/s/shm_open.html

–
Kirk Russell Bridlewood Software Testers Guild