Chapter 5. Advanced board driver functions
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## Chapter 5. Advanced board driver functions

This chapter describes the advanced functionality of the NAND driver. For a list of functions which can be overridden by the board driver see the documentation of the nand_chip structure.

## Multiple chip control

The nand driver can control chip arrays. Therefor the board driver must provide an own select_chip function. This function must (de)select the requested chip. The function pointer in the nand_chip structure must be set before calling nand_scan(). The maxchip parameter of nand_scan() defines the maximum number of chips to scan for. Make sure that the select_chip function can handle the requested number of chips.

The nand driver concatenates the chips to one virtual chip and provides this virtual chip to the MTD layer.

Note: The driver can only handle linear chip arrays of equally sized chips. There is no support for parallel arrays which extend the buswidth.

GPIO based example

    static void board_select_chip (struct mtd_info *mtd, int chip)
    {
    	/* Deselect all chips, set all nCE pins high */
    	GPIO(BOARD_NAND_NCE) |= 0xff;
    	if (chip >= 0)
    		GPIO(BOARD_NAND_NCE) &= ~ (1 << chip);
    }

Address lines based example. Its assumed that the nCE pins are connected to an address decoder.

    static void board_select_chip (struct mtd_info *mtd, int chip)
    {
    	struct nand_chip *this = (struct nand_chip *) mtd->priv;

    	/* Deselect all chips */
    	this->IO_ADDR_R &= ~BOARD_NAND_ADDR_MASK;
    	this->IO_ADDR_W &= ~BOARD_NAND_ADDR_MASK;
    	switch (chip) {
    	case 0:
    		this->IO_ADDR_R |= BOARD_NAND_ADDR_CHIP0;
    		this->IO_ADDR_W |= BOARD_NAND_ADDR_CHIP0;
    		break;
    	....
    	case n:
    		this->IO_ADDR_R |= BOARD_NAND_ADDR_CHIPn;
    		this->IO_ADDR_W |= BOARD_NAND_ADDR_CHIPn;
    		break;
    	}
    }

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