环境：dm8168+dvrrdk4.0.0.2
除了前3个寄存器有数据，其他寄存器为什么都是0x00？datasheet手册上有default值？是不是硬件电路有问题？
通过i2cset -f -y 2 0x3a addr value 可以修改寄存器的值
比如i2cset -f -y 2 0x3a 0x1e 0x07 (power down默认0x07)
修改成i2cset -f -y 2 0x3a 0x1e 0x0f (power down示波器测量XIN和XOP就没产生晶振波形)
证明是可以修改寄存器的，为什么读i2cget -f -y 2 0x3a 0x1e就是0x00呢？
root@HDMTerm:/mnt/work/test_dev/gpio_uart/gpio_uart_drv# i2cdump -f -y 2 0x3a
No size specified (using byte-data access)
0 1 2 3 4 5 6 7 8 9 a b c d e f 0123456789abcdef
00: 05 88 04 00 00 00 00 00 00 00 00 00 00 00 00 00 ???.............
10: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
20: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
30: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
40: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
50: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
60: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
70: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
80: 05 88 04 00 00 00 00 00 00 00 00 00 00 00 00 00 ???.............
90: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
a0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
b0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
c0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
d0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
e0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
f0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
root@HDMTerm:/mnt/work/test_dev/gpio_uart/gpio_uart_drv#
