On 1 Feb 2014, at 6:35 pm, Jeff Mitchell <[email protected]> wrote:
> For VGA, its busy much of the time .. Offhand I forget the details but the > dma is probably busy 75% of the time or more. > > The other device I'm talking to - for fun - is a Z80 which doesn't really > have peripherals per se, just a bus. A z180 has uart though (and a z80 can > use a SIO say, to get a uart); I've considered it but that would be pretty > slow bandwidth as well .. Say 38kbits/sec .. You can go much faster than that with the SIO; they were used in the Lantastic network adapters by Artisoft at 2Mbps. > I need to look up details .. But iirc the f405 haz 192k se as f429 disco; > isn't it 112K main sram, maybe 16Kb sram2 and 64Kb ccm? Maybe ccm is counted > separate .. If there is another 64KB on a different bus to main sram1 I might > be in luck. My framebuffer is around 64K. You should not think about “busses” - that isn’t how these chips work. There’s a set of crossbar switches (I wouldn’t be surprised if they are using the PL301) each with a set of slave and master ports connected to various things. It’s likely that AHB2 is cascaded off AHB1 (that would make sense with their clocking), but the important thing here is that SRAM2 is connected to a different port on the switch, so traffic for one doesn’t impact the other. There are FIFOs at various of the ports into / out of the fabric; these are the contended resource and you can find yourself stalled (or rate-bound) against other traffic fairly easily. I don’t recall what resolution you were talking about, but even 1024x668 @ 24bpp is only ~150MiB/sec. The fabric inside the STM32F4 is good for much more than that (even at 84MHz the base transfer rate is well over 300MiB/sec), so I think that latency is likely to be your issue. You mentioned trying to use the DRAM controller in the 429 - I looked at it a while back, and I recall that it is *very* slow (10+ cycles latency) in the normal-bad cases. It’d give you more frame buffer space, but you may run into issues trying to write to it while it’s being read out... ------------------------------------------------------------------------------ WatchGuard Dimension instantly turns raw network data into actionable security intelligence. It gives you real-time visual feedback on key security issues and trends. Skip the complicated setup - simply import a virtual appliance and go from zero to informed in seconds. http://pubads.g.doubleclick.net/gampad/clk?id=123612991&iu=/4140/ostg.clktrk _______________________________________________ libopencm3-devel mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/libopencm3-devel
