The number of gpio is calculated with blow formula
value = offset+ (port number* 8 + pin value)
Where offset is 320 if the group is main, and offset is 256 if the group is aon.
The pin12 of J41 on Nano devkit is I2S0_SCLK(GPIO3_PJ.07). So its GPIO number shoule be (320 + 9*8 + 7) = 320 + 79 = 399.
Why it is number 19?