Pmem很好的满足高通芯片中MDP、GPU等需要连续物理内存的设备,这里我稍微小结一些自己的理解,做个记录: 1.如何使用,这里要分两种情况: 第一种:在一个进程中自己分配自己使用,直接open之后mmap就ok了。 pmem_fd = open("/dev/pmem_device", O_RDWR, 0) pmem_base = mmap(0, size, PROT_READ|PROT_WRITE, MAP_SHARED, pmem_fd, 0) 第二种:需要在不同的进程中共享。这需要用到Pmem的Connect功能,先来理解下面的代码: pmem_fd0 = open("/dev/pmem_device", O_RDWR, 0) pmem_base = mmap(0, size, PROT_READ|PROT_WRITE, MAP_SHARED, pmem_fd0, 0) pmem_fd1 = open("/dev/pmem_device", O_RDWR, 0) ret = ioctl(pmem_fd1, PMEM_CONNECT, pmem_fd0) ret = ioctl(pmem_fd1 , PMEM_MAP, ®ion1) 通过Connect之后,pmem_fd1就获得了和pmem_fd0同样的Pmem空间。一个进程打开Pmem设备,通过mmap操作映射内存到进程 空间后,该进程成为了该Pmem的Master进程。其他进程通过Connect操作将自己的Pmem data和Master的Pmem data连接之后,就成为该Pmem的Client进程。在Android中,通过Binder, 实现了跨进程传递Pmem fd。相关代码见MemoryHeapBase.cpp和MemoryHeapPmem.cpp,具体使用可以看下面的简化代码: masterHeap = new MemoryHeapBase(Pmem_device,size,xxx)//对应主进程,申请Pmem clientHeap = new MemoryHeapPmem(masterHeap,xxx)//对应client进程,函数实现了connect操作 clientHeap->slap() //对应mmap操作 2. 理解了上面,就不难理解下面surface操作的过程了: client = new SurfaceComposerClient() //向Surfaceflinger申请一个Surface,surface类型为PushBuffers surfaceControl = client->createSurface(getpid(), 0, W, H,PIXEL_FORMAT_RGBA_565, ISurfaceComposer::ePushBuffers) //获取ISurface对象 isurface = Test::getISurface(surfaceControl) heap = new MemoryHeapBase(pmem_device, W * H) sp pmemHeap = new MemoryHeapPmem(heap, 0) pmemHeap->slap() mBufferHeap = ISurface::BufferHeap(W,H,PIXEL_FORMAT_BGRA_565, pmemHeap) isurface->registerBuffers(mBufferHeap) //得到buffer指针 char * bp = static_cast(mBufferHeap.heap->base()) //向buffer写位图数据,注意要是32位的 XXXXXXXXXX //提交修改,通知Surface Flinger更新屏幕 isurface->postBuffer(0) |
|
来自: shaobin0604@1... > 《Android》