如何使用SPI模式从SD卡中读取_单个_block(到目前为止,仍获得怪异的行为)?
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当我从SPI总线上的PIC-18F4520向卡发出地址(0x00000000)的cmd17时,我从命令发出中获得了正确的返回R1令牌。然后,经过几次循环检查,我从发出SPI_Put_Char(0xFF)的过程中得到了一个0xFE标记。然后应该开始数据,因此我将512个字节读取到IO_Buffer数组中。扫描退货时,我得到了很多0x00字节。奇怪的是,反复地,在扇区0的位置448处,一些数据传过来-到处都是几个字节-然后最后的32个字节(我只能在LCD屏幕上一次查看32个字节)全为零,然后是引导扇区末尾预期的0x55AA标记。
奇怪的是,使用磁盘调查器显示SD卡具有适当的扇区零信息-MSDOS消息,EB跳转代码,各种各样的东西。我的读取命令将所有内容都归零。我只是不知道发生了什么。
其他信息:我使用cmd0,cmd8,cmd58进行引导,OCR读取正常。然后是acmd41(先循环执行cmd55,然后再执行APP_SEND_OP_COND)。所有人似乎都做出了回应并给出了预期的指标。最后,我什至使用SEND_CID来获取卡信息。返回MID = 3 OID = SD和版本SD017后跟其他信息的消息-似乎都是正确的。
我尝试过在卡上的DOUT上添加上拉和下拉电阻,但不影响任何结果。
我迫切希望获得使该卡正确阅读的想法。我(顺便说一句)尝试了另外两张卡。它们给出了不同的特定结果,但是从质量上来说都是相同的-初始化,OCR和CID读取均可以正常进行。读取的数据大部分为零,后跟一些可重现但稀疏的字节,以及0xAA55标记!
我的SanDisk 1GB SD卡在3.296伏特下运行,在读卡过程中看起来很稳定。
这是一些代码:
bit MMC_Command(unsigned char cmd, unsigned short AdrH, unsigned short AdrL, unsigned char *response)
{
unsigned char response_length;
unsigned char MMC_Counter_Byte = 255;
unsigned char current_response;
switch (cmd)
{
case MMC_SEND_IF_COND:
case MMC_READ_OCR:
response_length = 5;
break;
case MMC_SEND_STATUS:
response_length = 2;
break;
default:
response_length = 1;
};
DEV_xSELECT = DEV_MMC;
SPI_Put_Char(cmd);
SPI_Put_Char(AdrH >> 8);
SPI_Put_Char(AdrH & 0x00FFU);
SPI_Put_Char(AdrL >> 8);
SPI_Put_Char(AdrL & 0x00FFU);
SPI_Put_Char(0x95U); //CRC = 0x95 to get to SPI, then value not important, so always use this for convenience
do
{
response[0] = SPI_Put_Char(0xFF);
} while ((response[0] & 0x80) && --MMC_Counter_Byte);
if (!MMC_Counter_Byte)
{
//SPI_Put_Char(0xFF); //some say is necessary
DEV_xSELECT = DEV_NONE;
return FALSE;
};
for (current_response = 1; current_response < response_length; current_response++)
{
response[current_response] = SPI_Put_Char(0xFF);
};
SPI_Put_Char(0xFF); //some say is necessary
DEV_xSELECT = DEV_NONE;
return TRUE;
};
unsigned char MMC_Init_SD(void)
{
unsigned long MMC_Counter_Word;
unsigned char response[5];
DEV_xSELECT = DEV_MMC;
for (MMC_Counter_Word = 0; MMC_Counter_Word < 20; MMC_Counter_Word++)
{
SPI_Put_Char(0xFFU);
};
DEV_xSELECT = DEV_NONE;
for (MMC_Counter_Word = 0; MMC_Counter_Word < 10; MMC_Counter_Word++)
{
SPI_Put_Char(0xFFU);
};
MMC_Counter_Word = 255;
do
{
MMC_Command(MMC_GO_IDLE_STATE, 0x0000, 0x0000, response); //cmd0
} while (--MMC_Counter_Word && (response[0] != 0x01));
if (!MMC_Counter_Word) //if counter timed out, error
{
return FALSE;
};
MMC_Command(MMC_SEND_IF_COND, 0x0000, 0x01AA, response); //cmd8
if (response[0] != 0x05)
{
return FALSE; //other card type
};
MMC_Command(MMC_READ_OCR, 0x0000, 0x0000, response); //cmd58
MMC_Counter_Word = 0xFFFFU;
do
{
if (MMC_Command(MMC_APP_CMD, 0x0000, 0x0000, response)) //cmd55
{
MMC_Command(MMC_APP_SEND_OP_COND, 0x4001, 0x0000, response); //acmd41
SPI_Put_Char(0xFF);
}
else
{
return FALSE;
};
} while (--MMC_Counter_Word && ((response[0] & 1) == 1));
if (!MMC_Counter_Word)
{
return FALSE;
};
if (MMC_Command(MMC_SEND_CID, 0x0000, 0x0000, response)) //cmd10
{
DEV_xSELECT = DEV_MMC;
MMC_Counter_Word = 255;
while (--MMC_Counter_Word && (SPI_Put_Char(0xFF) != 0xFE));
if (!MMC_Counter_Word)
{
DEV_xSELECT = DEV_NONE;
return FALSE;
};
//code for reading 16 byte OCR goes here
SPI_Put_Char(0xFFU);
SPI_Put_Char(0xFFU); //cycle through 16-bit CRC
SPI_Put_Char(0xFFU); //1GB Sandisk SD seems to require another dummy
DEV_xSELECT = DEV_NONE;
Delay_Sec(2);
LCD_CLS();
}
else
{
return FALSE;
};
return TRUE;
};
bit MMC_Fill_IO_Buffer(unsigned long sector)
{
unsigned short MMC_Fill_Index_Byte;
unsigned char MMC_Counter_Byte = 255;
unsigned char response[1];
if (MMC_Command(MMC_READ_SINGLE_BLOCK, 0x0000, 0x0000, response)) //cmd10
{
DEV_xSELECT = DEV_MMC;
MMC_Counter_Byte = 255;
while (--MMC_Counter_Byte && (SPI_Put_Char(0xFF) != 0xFE));
if (!MMC_Counter_Byte)
{
DEV_xSELECT = DEV_NONE;
return FALSE;
};
}
else
{
return FALSE;
};
for (MMC_Fill_Index_Byte = 0; MMC_Fill_Index_Byte < 512 ; MMC_Fill_Index_Byte++)
{
IO_Buffer[MMC_Fill_Index_Byte] = SPI_Put_Char(0xFF);
};
SPI_Put_Char(0xFFU);
SPI_Put_Char(0xFFU); //cycle through 16-bit CRC
SPI_Put_Char(0xFFU); //1GB Sandisk SD seems to require another dummy
DEV_xSELECT = DEV_NONE;
//following is IO_Buffer displaying code.
//LCD_CLS();
//for (MMC_Counter_Byte = 0; MMC_Counter_Byte < 42; MMC_Counter_Byte++)
//{
// LCD_Draw_Byte_Hex(IO_Buffer[MMC_Counter_Byte + 448]);
//};
//while (1);
return TRUE;
};
提前谢谢!
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