u8 MSD_ReadBlock(u8* pBuffer, u32 ReadAddr, u16 NumByteToRead)
{
u32 i = 0;
u8 rvalue = MSD_RESPONSE_FAILURE;
/* MSD chip select low */
MSD_CS_LOW();
/* Send CMD17 (MSD_READ_SINGLE_BLOCK) to read one block */
MSD_SendCmd(MSD_READ_SINGLE_BLOCK, ReadAddr, 0xFF);
/* Check if the MSD acknowledged the read block command: R1 response (0x00: no errors) */
if (!MSD_GetResponse(MSD_RESPONSE_NO_ERROR))
{
/* Now look for the data token to signify the start of the data */
if (!MSD_GetResponse(MSD_START_DATA_SINGLE_BLOCK_READ))
{
/* Read the MSD block data : read NumByteToRead data */
for (i = 0; i < NumByteToRead; i++)
{
/* Save the received data */
*pBuffer = MSD_ReadByte();
/* Point to the next location where the byte read will be saved */
pBuffer++;
}
/* Get CRC bytes (not really needed by us, but required by MSD) */
MSD_ReadByte();
MSD_ReadByte();
/* Set response value to success */
rvalue = MSD_RESPONSE_NO_ERROR;
}
}
/* MSD chip select high */
MSD_CS_HIGH();
/* Send dummy byte: 8 Clock pulses of delay */
MSD_WriteByte(DUMMY);
/* Returns the reponse */
return rvalue;
}
其中有一句if (!MSD_GetResponse(MSD_START_DATA_SINGLE_BLOCK_READ))为什么不成立 |
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