[libre-riscv-dev] Fall 2022 Interfaces

[Hendrik Boom]

On Fri, Jun 12, 2020 at 02:30:42PM +0100, Luke Kenneth Casson Leighton wrote:
> On Fri, Jun 12, 2020 at 1:38 PM Yehowshua <yimmanuel3 at gatech.edu> wrote:
> >
> >
> > > that may not be enough to handle framebuffers as well as run an OS.
> > > framebuffers are scarily demanding of memory bandwidth and they absolutely
> > > MUST have total absolute top priority.
> >
> >
> >  The OMI interface has 3200MT/s which is the same spec as DDR4.
> 
> 3200 million transactions/sec, let's assume 8 bytes.  that's 3200
> megabytes per second.  25 gigabit / 8 equals 3.125 so that fits with
> the math , there.  one 25 gigabit lane provides 3200 million 8-bit
> transactions per second (3.125).
> 
> 4k is 1200 megabytes per second: 37.5% *percent* of the total memory
> bandwidth consumed by a 4k 60fps framebuffer!  and if people wanted
> 120 fps instead, that's now a staggering 75% of a single OMI interface
> dedicated to the framebuffer!
> 
> bear in mind that that is *just* the framebuffer hardware.  the CPU -
> the GPU - is contending for the exact same memory resource.
> 

It's just possibe that we may not *need* 4k at 120 fps.
Certainly there are many potential applications for our chip that don't 
need that kind of video. 

-- hendrik