Re: Stupid user with user-space questions, matrix LED driving with user space code only.

2013-02-18 Thread el es
Jonathan Andrews jonshouse.co.uk> writes: > > What about a yield alignment mechanism for user space. IE the process > calls the kernel with a request "schedule me first after a yeild" - then > the process at least has whatever the timer granularity is to do > something timing critical... add a

Re: Stupid user with user-space questions, matrix LED driving with user space code only.

2013-02-17 Thread Jonathan Andrews
On Sun, 2013-02-17 at 18:05 -0800, Greg KH wrote: > On Sun, Feb 17, 2013 at 02:37:24PM +, Jonathan Andrews wrote: > > From a user perspective it seems a bit crap to have to change the kernel > > if you have a workload that preemption is harmful to. > > In the case of something like the Raspb

Re: Stupid user with user-space questions, matrix LED driving with user space code only.

2013-02-17 Thread Greg KH
On Sun, Feb 17, 2013 at 02:37:24PM +, Jonathan Andrews wrote: > From a user perspective it seems a bit crap to have to change the kernel > if you have a workload that preemption is harmful to. > In the case of something like the Raspberry Pi changing the kernel if > the distribution has not d

Re: Stupid user with user-space questions, matrix LED driving with user space code only.

2013-02-17 Thread anish kumar
On Sun, 2013-02-17 at 14:37 +, Jonathan Andrews wrote: > > > The dim pixel code is timing critical (but as I said only a tiny > > > fraction of the total CPU usage). What I need to do is grab the CPU and > > > prevent any context switch (IRQ or PREEMPT) for this period. > > why you want to do t

Re: Stupid user with user-space questions, matrix LED driving with user space code only.

2013-02-17 Thread Jonathan Andrews
> > The dim pixel code is timing critical (but as I said only a tiny > > fraction of the total CPU usage). What I need to do is grab the CPU and > > prevent any context switch (IRQ or PREEMPT) for this period. > why you want to do this? Because I need an I/O pin to change state for a short accurat

Re: Stupid user with user-space questions, matrix LED driving with user space code only.

2013-02-16 Thread anish kumar
On Sat, 2013-02-16 at 14:37 +, Jonathan Andrews wrote: > I hope this is the correct place, I expect to get abused. > > I'm trying to do a mostly soft real-time task with a very small hard > real time element. > > I've written some code to drive matrix LED signs using a Raspberry Pi. > > Sour

Stupid user with user-space questions, matrix LED driving with user space code only.

2013-02-16 Thread Jonathan Andrews
I hope this is the correct place, I expect to get abused. I'm trying to do a mostly soft real-time task with a very small hard real time element. I've written some code to drive matrix LED signs using a Raspberry Pi. Source here: http://www.jonshouse.co.uk/download/128x32_red_green_led_sign.tar.