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;
	}	
}