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Cosmos OpenSSD--greedy_ftl1.2.0（二）

FTL的整个流程如下：

下面先来看写的流程：

写的代码如下：

 1         if((hostCmd.reqInfo.Cmd == IDE_COMMAND_WRITE_DMA) ||  (hostCmd.reqInfo.Cmd == IDE_COMMAND_WRITE))
 2             {
 3 //                xil_printf("write(%d, %d)
", hostCmd.reqInfo.CurSect, hostCmd.reqInfo.ReqSect);
 4 
 5                 PrePmRead(&hostCmd, RAM_DISK_BASE_ADDR);
 6 
 7                 deviceAddr = RAM_DISK_BASE_ADDR + (hostCmd.reqInfo.CurSect % SECTOR_NUM_PER_PAGE)*SECTOR_SIZE;
 8                 reqSize = hostCmd.reqInfo.ReqSect * SECTOR_SIZE;
 9                 scatterLength = hostCmd.reqInfo.HostScatterNum;
10 
11                 DmaHostToDevice(&hostCmd, deviceAddr, reqSize, scatterLength);
12 
13                 PmWrite(&hostCmd, RAM_DISK_BASE_ADDR);
14 
15                 CompleteCmd(&hostCmd);
16             }

首先来看PrePmRead，其中最开始会涉及一个FlushPageBuf函数，FlushPageBuf里面有个FindFreePage函数，所以我们先分析FindFreePage函数的功能

lpn = hostCmd->reqInfo.CurSect / SECTOR_NUM_PER_PAGE;

u32 dieNo = lpn % DIE_NUM;

这里传入一个dieNo参数

 1 int FindFreePage(u32 dieNo)
 2 {
 3     blockMap = (struct bmArray*)(BLOCK_MAP_ADDR);
 4     dieBlock = (struct dieArray*)(DIE_MAP_ADDR);
 5 
 6     if(blockMap->bmEntry[dieNo][dieBlock->dieEntry[dieNo].currentBlock].currentPage == PAGE_NUM_PER_BLOCK-1)　　　　//当前块已经写完最后一页，则用下一个block
 7     {
 8         dieBlock->dieEntry[dieNo].currentBlock++;
 9 
10         int i;
11         for(i=dieBlock->dieEntry[dieNo].currentBlock ; i<(dieBlock->dieEntry[dieNo].currentBlock + BLOCK_NUM_PER_DIE) ; i++)　　/*遍历整个die的所有block，到结尾之后又从开始找，直到找到一个可用的block*/
12         {
13             if((blockMap->bmEntry[dieNo][i % BLOCK_NUM_PER_DIE].free) && (!blockMap->bmEntry[dieNo][i % BLOCK_NUM_PER_DIE].bad))　　//块free且不是坏块就可用
14             {
15                 blockMap->bmEntry[dieNo][i % BLOCK_NUM_PER_DIE].free = 0;
16                 dieBlock->dieEntry[dieNo].currentBlock = i % BLOCK_NUM_PER_DIE;
17 
18 //                xil_printf("allocated free block: %4d at %d-%d
", dieBlock->dieEntry[dieNo].currentBlock, dieNo % CHANNEL_NUM, dieNo / CHANNEL_NUM);
19 
20                 return dieBlock->dieEntry[dieNo].currentBlock * PAGE_NUM_PER_BLOCK;　　　　　　//返回页号
21             }
22         }
23 
24         dieBlock->dieEntry[dieNo].currentBlock = GarbageCollection(dieNo);　　　　//整个die没有可用块之后就进行垃圾回收
25 
26 //        xil_printf("allocated free block by GC: %4d at %d-%d
", dieBlock->dieEntry[dieNo].currentBlock, dieNo % CHANNEL_NUM, dieNo / CHANNEL_NUM);
27 
28         return (dieBlock->dieEntry[dieNo].currentBlock * PAGE_NUM_PER_BLOCK) + blockMap->bmEntry[dieNo][dieBlock->dieEntry[dieNo].currentBlock].currentPage;
29     }
30     else　　　　//当前块还有页可用就直接接着上一页继续写
31     {
32         blockMap->bmEntry[dieNo][dieBlock->dieEntry[dieNo].currentBlock].currentPage++;
33         return (dieBlock->dieEntry[dieNo].currentBlock * PAGE_NUM_PER_BLOCK) + blockMap->bmEntry[dieNo][dieBlock->dieEntry[dieNo].currentBlock].currentPage;
34     }
35 }

由此可见，FindFreePage这个函数其实就是找一个可用的页，没有空间了就进行垃圾回收操作

接下来看上一级的函数FlushPageBuf

 1 void FlushPageBuf(u32 lpn, u32 bufAddr)
 2 {
 3     if (lpn == 0xffffffff)　　　　　　　　　　　　//最开始page缓存内是没有东西的，所以无需flush
 4         return;
 5 
 6     u32 dieNo = lpn % DIE_NUM;　　　　　　　　　　//计算出die number
 7     u32 dieLpn = lpn / DIE_NUM;　　　　　　　　  //计算出lpn在die中是第几个lpn，可以理解为die0上是lpn0，lpn16……对应为dieLpn0，dieLpn1
 8     u32 ppn = pageMap->pmEntry[dieNo][dieLpn].ppn;
 9 
10     if (ppn == 0xffffffff)　　　　//表示page缓存还没有写入ppn
11     {
12         u32 freePageNo = FindFreePage(dieNo);
13 
14 //        xil_printf("free page: %6d(%d, %d, %4d)
", freePageNo, dieNo%CHANNEL_NUM, dieNo/CHANNEL_NUM, freePageNo/PAGE_NUM_PER_BLOCK);
15 
16         WaitWayFree(dieNo % CHANNEL_NUM, dieNo / CHANNEL_NUM);
17         SsdProgram(dieNo % CHANNEL_NUM, dieNo / CHANNEL_NUM, freePageNo, bufAddr);
18         WaitWayFree(dieNo % CHANNEL_NUM, dieNo / CHANNEL_NUM);
19 
20         // pageMap update
21         pageMap->pmEntry[dieNo][dieLpn].ppn = freePageNo;
22         pageMap->pmEntry[dieNo][freePageNo].lpn = dieLpn;
23     }
24 }

继续来看再上一级PrePmRead函数

int PrePmRead(P_HOST_CMD hostCmd, u32 bufferAddr)
{
    u32 lpn;
    u32 dieNo;
    u32 dieLpn;

    pageMap = (struct pmArray*)(PAGE_MAP_ADDR);
    lpn = hostCmd->reqInfo.CurSect / SECTOR_NUM_PER_PAGE;

    if (lpn != pageBufLpn)　　//新的请求和上个请求不是同一个lpn
    {
        FlushPageBuf(pageBufLpn, bufferAddr);

上面这一段进行了FlushPageBuf操作

        if((((hostCmd->reqInfo.CurSect)%SECTOR_NUM_PER_PAGE) != 0)
                    || ((hostCmd->reqInfo.CurSect / SECTOR_NUM_PER_PAGE) == (((hostCmd->reqInfo.CurSect)+(hostCmd->reqInfo.ReqSect))/SECTOR_NUM_PER_PAGE)))
        {
            dieNo = lpn % DIE_NUM;
            dieLpn = lpn / DIE_NUM;

            if(pageMap->pmEntry[dieNo][dieLpn].ppn != 0xffffffff)
            {
//                xil_printf("PrePmRead pdie, ppn = %d, %d
", dieNo, pageMap->pmEntry[dieNo][dieLpn].ppn);

                WaitWayFree(dieNo % CHANNEL_NUM, dieNo / CHANNEL_NUM);
                SsdRead(dieNo % CHANNEL_NUM, dieNo / CHANNEL_NUM, pageMap->pmEntry[dieNo][dieLpn].ppn, bufferAddr);
                WaitWayFree(dieNo % CHANNEL_NUM, dieNo / CHANNEL_NUM);

                pageBufLpn = lpn;
            }
        }
    }

疑问：这个判断条件第一个是请求开端不要是每个lpn的开始，第二个是请求的大小在同一页，那么这个条件就是只要满足不是请求跨页且从一个lpn的开始的就进入判断？有什么实际意义呢？

答：这里很关键，涉及一段数据，假如开始的地方没有和page对齐的话，那么在每个page里面请求开始前面的数据就得先读出来，如果是缓存命中的话，就无需操作，因为可以直接修改，那么没命中的话，即使是page对齐了，如果数据没有跨页的话，也还是要读出来，不然请求末尾内page的内容就丢失了。如下图

假如我要改写345678这些数据，因为数据是按页保存的，所以我只修改这些数据的话，我还得绿色部分的读取出来，然后修改后一起保存到一个页里面，所以请求的开始的lpn如果不是页对齐，我就得read-modify-write，同理，即使页对齐了，但是数据不足一页，那么一页后面几项数据也得先读出来。如果对齐且大小刚好等于一页的话，if失败，这个时候一页也是刚好可以直接修改。至于中间页的数据，本来就是一整页的，所以直接把原来的页无效，然后写入新页即可。这里这个判断条件是在页缓存没有命中的情况下，如果命中了，因为此页还没有刷新到nandflash，所以就无需取出而直接在SDRAM里面修改就行了

    if(((((hostCmd->reqInfo.CurSect)+(hostCmd->reqInfo.ReqSect))% SECTOR_NUM_PER_PAGE) != 0)
            && ((hostCmd->reqInfo.CurSect / SECTOR_NUM_PER_PAGE) != (((hostCmd->reqInfo.CurSect)+(hostCmd->reqInfo.ReqSect))/SECTOR_NUM_PER_PAGE)))
    {
        lpn = ((hostCmd->reqInfo.CurSect)+(hostCmd->reqInfo.ReqSect))/SECTOR_NUM_PER_PAGE;
        dieNo = lpn % DIE_NUM;
        dieLpn = lpn / DIE_NUM;

        if(pageMap->pmEntry[dieNo][dieLpn].ppn != 0xffffffff)
        {

//            xil_printf("PrePmRead pdie, ppn = %d, %d
", dieNo, pageMap->pmEntry[dieNo][dieLpn].ppn);

            WaitWayFree(dieNo % CHANNEL_NUM, dieNo / CHANNEL_NUM);
            SsdRead(dieNo % CHANNEL_NUM, dieNo / CHANNEL_NUM, pageMap->pmEntry[dieNo][dieLpn].ppn,
                    bufferAddr + ((((hostCmd->reqInfo.CurSect)% SECTOR_NUM_PER_PAGE) + hostCmd->reqInfo.ReqSect)/SECTOR_NUM_PER_PAGE*PAGE_SIZE));
            WaitWayFree(dieNo % CHANNEL_NUM, dieNo / CHANNEL_NUM);
        }
    }

    return 0;
}

上面是头，那这一部分就是尾，尾部如果不是请求对齐到page尾的话，那么也会有数据得不到更新，就如同上图lpn1的9到15，要把page内没修改的数据一起读出来更新，这里不仅是要不是结尾，而且是要跨页，这里分几种情况，假如缓存命中，没有跨页的话直接更新缓存就行了，只有跨页了，才需要进行read-modify-write操作；假如缓存没有命中，系统先把之前的缓存flush到nandflash里面，如果此时数据没有跨页的话，那么上面的操作就已经会读取那个页，也就无需下面再多此一举了，具体的写操作可以看下一篇文档。

接下来来看真正的写操作PmWrite

 1 int PmWrite(P_HOST_CMD hostCmd, u32 bufferAddr)
 2 {
 3     u32 tempBuffer = bufferAddr;
 4     
 5     u32 lpn = hostCmd->reqInfo.CurSect / SECTOR_NUM_PER_PAGE;
 6     
 7     int loop = (hostCmd->reqInfo.CurSect % SECTOR_NUM_PER_PAGE) + hostCmd->reqInfo.ReqSect;
 8     
 9     u32 dieNo;
10     u32 dieLpn;
11     u32 freePageNo;
12 
13     pageMap = (struct pmArray*)(PAGE_MAP_ADDR);
14 
15     // page buffer utilization
16     if (lpn != pageBufLpn)
17         pageBufLpn = lpn;
18 
19     UpdateMetaForOverwrite(lpn);
20 
21     // pageMap update
22     dieNo = lpn % DIE_NUM;
23     dieLpn = lpn / DIE_NUM;
24     pageMap->pmEntry[dieNo][dieLpn].ppn = 0xffffffff;　　　　//写入一页不立即更新
25 
26     lpn++;
27     tempBuffer += PAGE_SIZE;
28     loop -= SECTOR_NUM_PER_PAGE;
29 
30     while(loop > 0)　　//接下来还有页请求的话，寻找新页，写入，更新页表
31     {
32         dieNo = lpn % DIE_NUM;
33         dieLpn = lpn / DIE_NUM;
34         freePageNo = FindFreePage(dieNo);
35 
36 //        xil_printf("free page: %6d(%d, %d, %4d)
", freePageNo, dieNo%CHANNEL_NUM, dieNo/CHANNEL_NUM, freePageNo/PAGE_NUM_PER_BLOCK);
37 
38         WaitWayFree(dieNo % CHANNEL_NUM, dieNo / CHANNEL_NUM);
39         SsdProgram(dieNo % CHANNEL_NUM, dieNo / CHANNEL_NUM, freePageNo, tempBuffer);
40         
41         UpdateMetaForOverwrite(lpn);
42 
43         // pageMap update
44         pageMap->pmEntry[dieNo][dieLpn].ppn = freePageNo;
45         pageMap->pmEntry[dieNo][freePageNo].lpn = dieLpn;
46 
47         lpn++;
48         tempBuffer += PAGE_SIZE;
49         loop -= SECTOR_NUM_PER_PAGE;
50     }
51 
52     int i;
53     for(i=0 ; i<DIE_NUM ; ++i)
54         WaitWayFree(i%CHANNEL_NUM, i/CHANNEL_NUM);
55 
56     return 0;
57 }

接下来看读

 1 int PmRead(P_HOST_CMD hostCmd, u32 bufferAddr)
 2 {
 3     u32 tempBuffer = bufferAddr;
 4     
 5     u32 lpn = hostCmd->reqInfo.CurSect / SECTOR_NUM_PER_PAGE;
 6     int loop = (hostCmd->reqInfo.CurSect % SECTOR_NUM_PER_PAGE) + hostCmd->reqInfo.ReqSect;
 7     
 8     u32 dieNo;
 9     u32 dieLpn;
10 
11     pageMap = (struct pmArray*)(PAGE_MAP_ADDR);
12 
13     if (lpn == pageBufLpn)　　//缓存命中，就无需读取第一页，直接就在内存里面
14     {
15         lpn++;
16         tempBuffer += PAGE_SIZE;
17         loop -= SECTOR_NUM_PER_PAGE;
18     }
19     else
20     {
21         dieNo = lpn % DIE_NUM;
22         dieLpn = lpn / DIE_NUM;
23 
24         if(pageMap->pmEntry[dieNo][dieLpn].ppn != 0xffffffff)　　　　//防止第一次读空页
25         {
26             FlushPageBuf(pageBufLpn, bufferAddr);
27             pageBufLpn = lpn;
28         }
29     }
30 
31     while(loop > 0)　　　　//把接下来的页一次读取出来
32     {
33         dieNo = lpn % DIE_NUM;
34         dieLpn = lpn / DIE_NUM;
35 
36 //        xil_printf("requested read lpn = %d
", lpn);
37 //        xil_printf("read pdie, ppn = %d, %d
", dieNo, pageMap->pmEntry[dieNo][dieLpn].ppn);
38 
39         if(pageMap->pmEntry[dieNo][dieLpn].ppn != 0xffffffff)
40         {
41 //            xil_printf("read at (%d, %2d, %4x)
", dieNo%CHANNEL_NUM, dieNo/CHANNEL_NUM, pageMap->pmEntry[dieNo][dieLpn].ppn);
42 
43             WaitWayFree(dieNo % CHANNEL_NUM, dieNo / CHANNEL_NUM);
44             SsdRead(dieNo % CHANNEL_NUM, dieNo / CHANNEL_NUM, pageMap->pmEntry[dieNo][dieLpn].ppn, tempBuffer);
45         }
46 
47         lpn++;
48         tempBuffer += PAGE_SIZE;
49         loop -= SECTOR_NUM_PER_PAGE;
50     }
51 
52     int i;
53     for(i=0 ; i<DIE_NUM ; ++i)
54         WaitWayFree(i%CHANNEL_NUM, i/CHANNEL_NUM);
55 
56     return 0;
57 }

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原文地址：https://www.cnblogs.com/losing-1216/p/4930523.html