DM365 OSD Memory DDR 映射 及寄存器说明

先是获得DMA的内存映射（一致性DMA映射）

/* allocate the framebuffer */info->screen_base =    dma_alloc_coherent(dev, info->fix.smem_len,       (dma_addr_t *) & info->fix.smem_start,       GFP_KERNEL | GFP_DMA);

然后去设置寄存器，以让硬件去搬运从 info->fix.smem_start 的物理地址开始 缓存

从代码上分析，这里的fb_offset_32就是info->fix.smem_start 物理地址

  fb_offset_32 = fb_offset_32 >> 5;

  case WIN_OSD0:   osd_merge(OSD_OSDWIN0OFST_O0AH,     ((fb_offset_32 & 0x7800000) >>     (23 - OSD_WINOFST_AH_SHIFT)) | 0x1000,      OSD_OSDWIN0OFST);   osd_merge(OSD_OSDWINADH_O0AH,     (fb_offset_32 & 0x7F0000) >>     (16 - OSD_OSDWINADH_O0AH_SHIFT),      OSD_OSDWINADH);   osd_write(fb_offset_32 & 0xFFFF, OSD_OSDWIN0ADL);   break;

下面的表格给出了 应写入 frame buffer address 到OSD 寄存器的 关系

Frame buffer address

OSD registers base address = 0x1c71c00

bit

bit

offset

Register name

description

[31-28]

bit[12-9]

20h 

OSDWIN0OFST

Bitmap Window 0 Offset

[27-21]

bit[6-0]

34h

OSDWINADH

BMP Window 0/1 Address - High 

[20-5]

bit[12-0]

38h

OSDWIN0ADL

BMP Window 0 Address - Low

[5-0] 丢弃

 

 

 

 

也就是

DM365: start address is 27-bit long address b26 - b23 are in offset register b12 - b9, and * bit 26 has to be '1'

* bit 26 has to be '1' 是因为物理地址起始是0x8000 0000