If you dig through the user-mode uio_pruss code, you will see that the PRU itself, the PRU memory and control registers, and the large shared buffer is all accessed via a mmap on the /dev/uio_pruss* device.
If you dig in the PRU kernel driver, you will see the dram shared buffer is allocated and handled as DMA memory. The dma_alloc_coherent() call used to allocate the memory grabs a physically contiguous chunk, provides physical and virtual addresses, and sets the page caching flags as needed for the architecture. On 2/10/2016 9:07 AM, Tyler Turcotte wrote: > I have been using the BeagleBone PRU and have been accessing and mapping > memory this way and thus far it seems as though it is one contiguous > address. I am relatively new to Beaglebone so maybe one of the more > experienced may want to step in on this one. > > Once I have used prussdrv_get_phys_addr to get the physical address it > seems to store to one contiguous memory and is limited to 8mb. > > I believe it is allocated contiguous from uio_pruss as well. > > > On Friday, February 5, 2016 at 7:33:59 PM UTC-5, Bill Gray wrote: >> >> Hi, >> >> I've got PRU0 of my BBB pulling in 12 Bytes of data from a ADC with a >> sampling frequency of 31250hz. >> >> I want to stash all of this data in an array that lives in DDR memory. I >> would like to make the array 0x4000 bytes (16kB) large. This would give me >> 1365 12 byte records and about 43ms of data to play with. >> >> I'm currently using prussdrv_map_extmem() to hook me up with the DDR >> memory. It provides me with a memory block that is 256kB, so I have plenty >> of room. >> >> The question I have is... can I count on the physical address in this >> 256kB block of memory to be contiguous? >> >> I'm pretty new to linux memory management, but I see that the "page size" >> is only 4kB... so I imagine that the virtual memory system might chop my >> 256kB block up into bits which might not necessarily have contiguous >> addresses. >> >> If I can count on contiguous addresses, this radically simplifies the >> memory access code in the PRU. If I can't... well, then I can't, and I've >> got to figure something else out. >> >> When I run experiments I see that the physical addresses are contiguous, >> but are they guaranteed to be? or has this just been "lucky"? >> >> Thanks, >> >> Bill >> >> >> > -- Charles Steinkuehler char...@steinkuehler.net -- For more options, visit http://beagleboard.org/discuss --- You received this message because you are subscribed to the Google Groups "BeagleBoard" group. To unsubscribe from this group and stop receiving emails from it, send an email to beagleboard+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/d/optout.
