Study Notes --- S3C2440 NANDFLASH operation principle and test code analysis

First, let's take a look at the NANDFLASH interface:

As can be seen from the figure, there are only data ports and control ports, but no address lines, so it cannot be uniformly addressed like a network card or SDRAM. Its operation steps are as follows:

1 Enable chip

2 Send operation instructions (read, write, erase, reset)

3 Send operation address

5 Waiting for the busy signal to be released (read only)

6 Send data (write), receive data (read)

7 Waiting for busy signal, low level busy

8 Disable Chip

These control signal lines are all set by software registers, and then the hardware automatically generates control signals for other control lines;

The meanings of the operation signals are as follows:

R/B: Read/Busy status line

CE : Chip Select

CLE: Send command signal

ALE: Send address signal

WE: Write signal

RE: Read signal

Things to note here:

1 Data is transmitted in bytes, and there are exactly 8 data lines. The data register can be read directly to obtain data.

2 The address has 32 bits, but there are only 8-bit lines here, so an address needs to be sent multiple times to complete. For the sending rules, see the NANDFLASH chip manual, as shown below:

This chip needs to send the address in 4 cycles. The number of address lines depends on the size of the memory chip. When writing the driver, the address bits must be sent according to this table.

@******************************************************************************

@ File：head.s

@ Function: Set up SDRAM, copy the program to SDRAM, and then jump to SDRAM to continue execution

@******************************************************************************       

.text

.global _start

_start:

                                            @Functions disable_watch_dog, memsetup, init_nand, nand_read_ll are defined in init.c

            ldr sp, =4096 @Set up the stack 

            bl      disable_watch_dog       @关WATCH DOG

            bl memsetup @ Initialize SDRAM

            bl nand_init @Initialize NAND Flash

                                            @Copy the 1024-byte code starting at address 4096 in NAND Flash (compiled from main.c) to SDRAM

                                            The @nand_read_ll function requires 3 parameters:

            ldr r0, =0x30000000 @1. Target address = 0x30000000, which is the starting address of SDRAM

            mov r1, #4096 @2. Source address = 4096. When linking, the code in main.c is stored at the beginning of NAND Flash address 4096.

            mov r2, #1024 @3. Copy length = 1024 (bytes), which is enough for main.c of this experiment

            bl nand_read @Call C function nand_read

            ldr sp, =0x34000000 @Set up the stack

            ldr lr, =halt_loop @Set the return address

            ldr pc, =main @b instruction and bl instruction can only jump forward and backward within the range of 32M, so here we use the method of assigning value to pc to jump

halt_loop:

            b       halt_loop

Let's look at this startup code first. In order to use C language to set the watchdog and initialize SDRAM and other operations, you need to set the SP first, because the entry address and local variables of the C language function need to be stored in the stack.

After initialization, you can call the nandread function to read the NANDFLSH data. Here, you need to pass in three parameters. To pass parameters from assembly language to C language functions, you can only assign the parameters to R0-R4. Here, the first parameter corresponds to r0, and so on. The following code implements passing parameters to the nand_read function:

            ldr r0, =0x30000000 @1. Target address = 0x30000000, which is the starting address of SDRAM

            mov r1, #4096 @2. Source address = 4096. When linking, the code in main.c is stored at the beginning of NAND Flash address 4096.

            mov r2, #1024 @3. Copy length = 1024 (bytes), which is enough for main.c of this experiment

            bl nand_read @Call C function nand_read

Let's look at the prototype of nand_read:

void nand_read(unsigned char *buf, unsigned long start_addr, int size)

The first parameter needs to be an address, so the address passed in from the assembly is an address, and the LDR instruction is used to load the absolute address into r0

dr r0, =0x30000000 @1. Target address = 0x30000000, which is the starting address of SDRAM

The second and third parameters passed in are immediate values, which can be assigned directly using the following method

mov r1, #4096 @2. Source address = 4096. When linking, the code in main.c is stored at the beginning of NAND Flash address 4096.

mov r2, #1024 @3. Copy length = 1024 (bytes), which is enough for main.c of this experiment