Dear Liu Hui-R64343,
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According to REV C manual, the register IOMUXC_IOMUXC_GPR4 has bits 4 and 5 read-only and the value is always set as zero. So write '0' to these bits instead of writing '1'.
Jason, Fabio: What do you think? You should be the datasheet 'masters' ;)
Yes, according to the RM, 5 Reserved This read-only field is reserved and always has the value 0. 4 Reserved This read-only field is reserved and always has the value 0.
So, write 1 should have no effect.
I really dislike how "write 1 should have no effect" sounds. Can you please check with HW people?
Since this is read-only bit, if you write 1 to it, it will have no effect.
For how long do you work with hardware? Did it never occur to you that when you wrote 1 to an "reserved" bit, it either did something you didn't expect or you had to rework it later because the new CPU has that bit for something else?
Yes, to avoid the confusion, for example to do the read-back check, I agree with not writing '1' to the read-only bit.
Please, ask the hardware people about this.
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Best regards, Marek Vasut
Best regards, Marek Vasut