[libre-riscv-dev] Fall 2022 Interfaces
hendrik at topoi.pooq.com
Fri Jun 12 15:06:51 BST 2020
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.
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