Nand flash read in ViVi

project     : dessect Nand read from Vivi
instruction : dessect Nand read from ViVi step by step.

(1) the below fragment from ViVi is represent for reading Nand flash to memory.

int nand_read_ll(unsigned char *buf, unsigned long start_addr, int size)
{
    int i, j;

    if ((start_addr & NAND_BLOCK_MASK) || (size & NAND_BLOCK_MASK)) {
        return -1;    /* invalid alignment */
    }

    NAND_CHIP_ENABLE;  // see comment [ comment A ]

    for(i=start_addr; i < (start_addr + size);) {
        /* READ0 */
        NAND_CLEAR_RB;    // see comment [ comment B ]
        NFCMD = 0;  see comment [ comment C ]

        /* Write Address */
        NFADDR = i & 0xff;            //see comment [ comment D ]
        NFADDR = (i >> 9) & 0xff;     //see comment [ comment D ]
        NFADDR = (i >> 17) & 0xff;    //see comment [ comment D ]
        NFADDR = (i >> 25) & 0xff;    //see comment [ comment D ]

        NAND_DETECT_RB;               //see comment [ comment E ]

        for(j=0; j < NAND_SECTOR_SIZE; j++, i++) {
            *buf = (NFDATA & 0xff);   //see comment [ comment F ]
            buf++;
        }
    }
    NAND_CHIP_DISABLE;  // [ comment A ]
    return 0;
}

======================================================================================
[ comment A ]

#define NAND_CHIP_ENABLE  (NFCONT &= ~(1<<1))
#define NAND_CHIP_DISABLE (NFCONT |=  (1<<1))

CONTROL REGISTER
------------------------------------------------------------------------------------
Register    Address     R/W    Description                              Reset Value
------------------------------------------------------------------------------------
NFCONT      0x4E000004  R/W    NAND flash control register              0x0384
------------------------------------------------------------------------------------

------------------------------------------------------------------------------------
NFCONT      Bit        Description                                     Initial State
------------------------------------------------------------------------------------
Reg_nCE     [1]        NAND Flash Memory nFCE signal control            1   
                       0: Force nFCE to low (Enable chip select)
                       1: Force nFCE to high (Disable chip select)
                       Note:  During boot time, it is controlled
                       automatically.
                       This value is only valid while MODE bit is 1
------------------------------------------------------------------------------------

======================================================================================
[ comment B ]

#define NAND_CLEAR_RB      (NFSTAT |=  (1<<2))

------------------------------------------------------------------------------------
NFSTAT          Bit    Description                                     Initial State
------------------------------------------------------------------------------------
RnB_TransDetect [2]    When RnB low to high transition is               0  
                       occurred, this value set and issue
                       interrupt if enabled. To clear this
                       value write ‘1’.
                       0: RnB transition is not detected
                       1: RnB transition is detected
                       Transition configuration is set in
                       RnB_TransMode (NFCONT[8]).
------------------------------------------------------------------------------------

------------------------------------------------------------------------------------
Pin                    Name Pin Function
------------------------------------------------------------------------------------
RnB                    READY/BUSY OUTPUT
                       The R/B output indicates the status of the device operation.
                       When low, it indicates that a program, erase or random read
                       operation is in process and returns to high state upon
                       completion. It is an open drain output and does not float to
                       high-z condition when the chip is deselected or when outputs
                       are disabled.
------------------------------------------------------------------------------------

======================================================================================
[ comment C ]

#define NFCMD       bNAND_CTL(0x08)

COMMAND REGISTER
------------------------------------------------------------------------------------
Register    Address      R/W        Description                         Reset Value
------------------------------------------------------------------------------------
NFCMMD      0x4E000008   R/W        NAND flash command set register     0x00
------------------------------------------------------------------------------------

------------------------------------------------------------------------------------
NFCMMD       Bit         Description                          Initial State
------------------------------------------------------------------------------------
Reserved     [15:8]      Reserved                             0x00
NFCMMD       [7:0]       NAND flash memory command value      0x00
------------------------------------------------------------------------------------

======================================================================================
[ comment D ]

#define NFADDR      bNAND_CTL(0x0c)

ADDRESS REGISTER
------------------------------------------------------------------------------------
Register     Address     R/W        Description                         Reset Value
------------------------------------------------------------------------------------
NFADDR       0x4E00000C  R/W        NAND flash address set register     0x0000XX00
------------------------------------------------------------------------------------

------------------------------------------------------------------------------------
REG_ADDR     Bit         Description                           Initial State
------------------------------------------------------------------------------------
Reserved     [15:8]      Reserved                              0x00
------------------------------------------------------------------------------------
NFADDR       [7:0]       NAND flash memory address value       0x00
------------------------------------------------------------------------------------

======================================================================================
[ comment E ]
#define NAND_DETECT_RB      { while(! (NFSTAT&(1<<2)) );}

#define NFSTAT      bNAND_CTL(0x20)

NFCON STATUS REGISTER
------------------------------------------------------------------------------------
Register    Address     R/W     Description                             Reset Value
------------------------------------------------------------------------------------
NFSTAT      0x4E000020  R/W     NAND flash operation status register    0xXX00
------------------------------------------------------------------------------------

------------------------------------------------------------------------------------
NFSTAT          Bit    Description                                     Initial State
------------------------------------------------------------------------------------
RnB_TransDetect [2]    When RnB low to high transition is               0  
                       occurred, this value set and issue
                       interrupt if enabled. To clear this
                       value write ‘1’.
                       0: RnB transition is not detected
                       1: RnB transition is detected
                       Transition configuration is set in
                       RnB_TransMode (NFCONT[8]).
------------------------------------------------------------------------------------

======================================================================================
[ comment F ]

#define NFDATA      __REGb(0x4e000000 + (0x10))

DATA REGISTER
------------------------------------------------------------------------------------
Register    Address     R/W   Description                              Reset Value
------------------------------------------------------------------------------------
NFDATA      0x4E000010  R/W   NAND flash data register                 0xXXXX
------------------------------------------------------------------------------------

------------------------------------------------------------------------------------
NFDATA    Bit      Description                                        Initial State
------------------------------------------------------------------------------------
NFDATA    [31:0]   NAND flash read/program data value for I/O          0xXXXX
                   Note:  Refer to data register configuration
                   in Page 6-5.
------------------------------------------------------------------------------------
======================================================================================