當我從SPI總線上的PIC-18F4520向我的卡發出地址爲(0x00000000)的cmd17時,我從命令問題得到正確的返回R1令牌。然後,在幾次循環檢查之後,我從發出的SPI_Put_Char(0xFF)返回一個0xFE標記。數據應該開始,所以我讀取512個字節到我的IO_Buffer數組中。當我掃描返回時,我得到了很多0x00字節。奇怪的是,在扇區0的第448位左右,有些數據會出現 - 幾個字節在這裏和那裏 - 然後是最後的32個字節(我一次只能在LCD屏幕上查看32個字節)都是零,然後是零預期在引導扇區末尾的0x55AA標記。如何使用SPI模式從SD卡read_single_block(到目前爲止還有怪異的行爲)?
奇怪的是,使用磁盤調查器顯示SD卡有適當的扇區零信息 - MSDOS消息,EB跳轉代碼,各種東西。我的閱讀命令將所有的內容都歸零。我只是不知道發生了什麼。
其他信息:我用cmd0,cmd8,cmd58啓動並且OCR讀取正常。然後acmd41(循環cmd55,然後是APP_SEND_OP_COND)。所有人似乎都回應並給出預期的標記。最後,我甚至使用SEND_CID來獲取卡信息。返回MID = 3 OID = SD和版本SD017後跟其他信息 - 似乎都是正確的。
我已經嘗試添加上拉並從卡上拉下DOUT上的電阻,但不影響任何結果。
我非常渴望嘗試讓這張卡片正確讀取。我有(順便說一句)嘗試了另外兩張牌。他們給出了不同的具體結果,但在性質上是相同的 - 初始化,OCR和CID讀取都可以。讀取的數據大多爲零,然後是一些可重現但稀疏的字節,並帶有一個0xAA55標記!
我的SanDisk 1GB SD卡運行電壓爲3.296伏,在讀卡過程中看起來很穩定。
下面是一些代碼:提前
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;
};
謝謝!
我有完全相同的問題,如下所述:http://electronics.stackexchange.com/questions/23053/problems-reading-data-from-a-microsd-card無法想到任何可能的原因。 – Armandas 2011-12-01 14:37:48