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H3芯片外接nand flash芯片，在调试uboot的时候，读写nfc寄存器的值都为0，其它控制器不是，这是什么问题？？
void board_nand_init(void)
{
printf("+++ board_nand_init +++\n");
nand_pinmux_setup();
nand_clock_setup();

struct sunxi_nfc_reg
{
uint32_t ndfc_ctl;
uint32_t ndfc_st;
uint32_t ndfc_int;
uint32_t ndfc_timing_ctl;
uint32_t ndfc_timing_cfg;
uint32_t ndfc_addr_low;
uint32_t ndfc_addr_high;
uint32_t ndfc_block_num;
uint32_t ndfc_cnt;
uint32_t ndfc_rcmd_set;
uint32_t ndfc_wcmd_set;
};

struct sunxi_gpio_reg const pio = (struct sunxi_gpio_reg )SUNXI_PIO_BASE;

printf("address: %p \n", &pio->gpio_bank[2].cfg[0]);
printf("value: 0x%x \n", readl(&pio->gpio_bank[2].cfg[0]));

struct sunxi_nfc_reg const nfc = (struct sunxi_nfc_reg )0x01C03000;

printf("ndfc->ndfc_wcmd_set: %p \n", &nfc->ndfc_wcmd_set);
printf("ndfc_wcmd_set: 0x%x \n", readl(&nfc->ndfc_wcmd_set));

#ifndef CONFIG_SPL_BUILD
sunxi_nand_init();
#endif
}

U-Boot SPL 2017.03 (May 17 2019 - 15:12:56)
DRAM: 512 MiB
Trying to boot from MMC1

U-Boot 2017.03 (May 17 2019 - 15:12:56 +0800) Allwinner Technology

CPU: Allwinner H3 (SUN8I 1680)
Model: Xunlong Orange Pi One
DRAM: 512 MiB
+++ initr_nand +++
NAND: +++ nand_init +++
+++ board_nand_init +++
address: 01c20848
value: 0x22222222
ndfc->ndfc_wcmd_set: 01c03028
ndfc_wcmd_set: 0x0
+++ sunxi_nand_init +++
+++ regs: 01c03000 +++
sunxi nfc reset successful!
chip: 0x0
ccm->nand0_clk_cfg: 01c20080
ccm->nand0_clk_cfg: 0x8102000a
ccm->sd0_clk_cfg: 01c20088
ccm->sd0_clk_cfg: 0x8140030b
ccm->pll6_cfg: 01c20028
ccm->pll6_cfg: 0x90041811
NFC_REG_TIMING_CTL: 0x0
NFC_REG_CTL: 0x0
NFC_REG_CTL: 0x0