uClinux2.6(bf561)的NorFlash驱动实现分析(1): 基本参数

 

   

下文开发环境为：AM29LV320MT（4M，16位），uclinux-2.6，VDSP4.5，bf561

在uClinux启动时可以看到类似的提示：

BF561 EZKIT Map: Found 1 x16 devices at 0x0 in 16-bit bank

它的输出是由：

       printk(KERN_INFO "%s: Found %d x%d devices at 0x%x in %d-bit bank/n",

              map->name, cfi->interleave, cfi->device_type*8, base,

              map->bankwidth*8);

进行控制的。这行信息揭示了NorFlash的一些基本参数：

l         map->bankwidth：MTD设备的接口总线宽度，其值可以为1，2或4。

l         cfi->interleave：交错数，几块芯片平行连接成一块芯片，使bankwidth变大。

l         cfi->device_type：单个芯片的总线宽度，其值为1、2或4。

l         device_addr：nor flash设备的总线地址(寻址)范围视具体芯片以及其采用的位宽而定。

对于位扩展来讲：bankwidth=device_type*interleave

如富士通的29LV650：其容量是8Mbyte，共128个sector，每个sector的大小是64 kbyte。如果选择位宽为x8，设备总线的每个地址代表了一个byte的存储单元，其总线地址范围为8M(0x000000~0x7fffff)。如果选择位宽为x16，设备总线的每个地址代表了两个byte的存储单元，固其总线地址范围为4M(0x000000~0x3fffff)。

再如intel的E29F128：其容量为16Mbyte，共128个sector，每个sector的大小是128Kbyte。如果选择位宽为x8，设备总线的每个地址代表了一个byte的存储单元，其总线地址范围为16M(0x000000~0xffffff)。如果选择位宽为x16，这时候设备的A0脚不可用，所以不能访问到奇地址的存储单元，而只能0、2、4...地址的来访问，其总线地址范围为8M(0x000000~0xffffff的偶地址)。

在uClinux进行芯片检测时就充分考虑了各种可能的接线方式：

static int genprobe_new_chip(struct map_info *map, struct chip_probe *cp,

                   struct cfi_private *cfi)

{

     int min_chips = (map_bankwidth(map)/4?:1); /* At most 4-bytes wide. */

     int max_chips = map_bankwidth(map); /* And minimum 1 */

     int nr_chips, type;

 

     for (nr_chips = max_chips; nr_chips >= min_chips; nr_chips >>= 1) {

 

         if (!cfi_interleave_supported(nr_chips))

             continue;

 

         cfi->interleave = nr_chips;

 

         /* Minimum device size. Don't look for one 8-bit device

            in a 16-bit bus, etc.

            每个芯片的位宽 = (总线宽度 / 芯片数量)。

*/

         type = map_bankwidth(map) / nr_chips;

        

         for (; type <= CFI_DEVICETYPE_X32; type<<=1) {

              cfi->device_type = type;

 

              if (cp->probe_chip(map, 0, NULL, cfi))

                   return 1;

         }

     }

     return 0;

}

在向norflash发送命令并读取flash的响应结果时则考虑到设备地址的问题：

 

/*

 * Returns the command address according to the given geometry.

 */

static inline uint32_t cfi_build_cmd_addr(uint32_t cmd_ofs, int interleave, int type)

{

     return (cmd_ofs * type) * interleave;

}

 

/*

 * Transforms the CFI command for the given geometry (bus width & interleave).

*/

map_word cfi_build_cmd(u_long cmd, struct map_info *map, struct cfi_private *cfi)

{

     map_word val = { {0} };

     int wordwidth, words_per_bus, chip_mode, chips_per_word;

     unsigned long onecmd;

     int i;

 

     /* We do it this way to give the compiler a fighting chance

        of optimising away all the crap for 'bankwidth' larger than

        an unsigned long, in the common case where that support is

        disabled */

     if (map_bankwidth_is_large(map)) {

         wordwidth = sizeof(unsigned long);

         words_per_bus = (map_bankwidth(map)) / wordwidth; // i.e. normally 1

     } else {

         wordwidth = map_bankwidth(map);

         words_per_bus = 1;

     }

 

     chip_mode = map_bankwidth(map) / cfi_interleave(cfi);

     chips_per_word = wordwidth * cfi_interleave(cfi) / map_bankwidth(map);

 

     /* First, determine what the bit-pattern should be for a single

        device, according to chip mode and endianness... */

     switch (chip_mode) {

     default: BUG();

     case 1:

         onecmd = cmd;

         break;

     case 2:

         onecmd = cpu_to_cfi16(cmd);

         break;

     case 4:

         onecmd = cpu_to_cfi32(cmd);

         break;

     }

 

     /* Now replicate it across the size of an unsigned long, or

        just to the bus width as appropriate */

     switch (chips_per_word) {

     default: BUG();

#if BITS_PER_LONG >= 64

     case 8:

         onecmd |= (onecmd << (chip_mode * 32));

#endif

     case 4:

         onecmd |= (onecmd << (chip_mode * 16));

     case 2:

         onecmd |= (onecmd << (chip_mode * 8));

     case 1:

         ;

     }

 

     /* And finally, for the multi-word case, replicate it

        in all words in the structure */

     for (i=0; i < words_per_bus; i++) {

         val.x[i] = onecmd;

     }

 

     return val;

}

 

/*

 * Sends a CFI command to a bank of flash for the given geometry.

 *

 * Returns the offset in flash where the command was written.

 * If prev_val is non-null, it will be set to the value at the command address,

 * before the command was written.

 */

uint32_t cfi_send_gen_cmd(u_char cmd, uint32_t cmd_addr, uint32_t base,

                   struct map_info *map, struct cfi_private *cfi,

                   int type, map_word *prev_val)

{

     map_word val;

     uint32_t addr = base + cfi_build_cmd_addr(cmd_addr, cfi_interleave(cfi), type);

 

     val = cfi_build_cmd(cmd, map, cfi);

 

     if (prev_val)

         *prev_val = map_read(map, addr);

 

     map_write(map, val, addr);

 

     return addr - base;

}