I’m trying to convert the i2c-dev.h file into Julia. I am having problems converting a C union to Julia, a couple of structs, and how to pass a struct to a ccall(). I’ll show the C code first then the Julia code. The C code: /* * I2C Message - used for pure i2c transaction, also from /dev interfa…

[edit: the below code is all wrong, as yuyichao pointed out. I think he answered your question in the other thread, so I’ll refrain from correcting my post and just keep it for my eternal shame. Thanks!] For your union, you could try something like: type i2c_smbus_data Block::Vector{UInt8} …

[image] foobar_lv: Block::Vector{UInt8} Wrong alignment. Ref Dereference a pointer - #5 by Frank_Applin

@yuyichao in the other thread you said: I posted another question about converting C unions to Julia and C structs with unions in them and I’ve got no answers. Because that’s not possible in general. A C union is just a struct with the alignment of the largest member (plus some syntax sugar…

[image] ihnorton: A C union is just a struct with the alignment of the largest member (plus some syntax sugar). No, it has at least the size of the largest member and the alignment of the most aligned member, not the largest member. So that doc is wrong.

Maybe, if there is an answer to the union issue - this could be added to the documentation under Callling C and Fortran. Unions are commonly used in C and it would probably benefit many if it were in the documentation with a couple of examples. On Sat, Oct 7, 2017 at 8:19 AM, Yichao Yu julialang@dis…

Alright, thanks for the correction. I think the doc is basically accurate in that it mentions the potential need for padding as a parenthetical (Jameson wrote the paragraph).

OK. I have the whole i2c-dev.c converted to Julia. I am having problems with how to define the ccall (again). I’ve been to the Calling C and Fortran documentation and there are no examples of how to pass a struct. Can you help again? I’m sorry to be so ignorant on this stuff. Here’s the C Code: #d…

[image] Frank_Applin: I figured i2c_smbus_data can just become a data::Vector{UInt8} I’m pretty sure this is at least the third time I talked about this in this and previous thread but no you can’t, the alignment is wrong. You have to use Vector{UInt16} or NTuple{N,UInt16}.

[image] Frank_Applin: read_write::UInt8 command::UInt8 size::UInt32 data::Vector{UInt8} And this is wrong. There’s no equivalent of Vector in C. You have to store a pointer to a struct here. You can do that with. mutable struct i2c_smbus_data block::NTuple{(I2C_SMBUS_BLOCK_MAX + 1) ÷ …

Alternatively, if this struct will not be passed around, you can directly store a pointer there (and use @gc_preserve to make sure the object owning that pionter is alive during the ccall). You still need to make sure that the data has the right alignment though.

Help converting C code (i2c-dev)

General Usage

yuyichao October 6, 2017, 9:56pm 3

Wrong alignment. Ref Dereference a pointer - #5 by Frank_Applin

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Help converting C code (i2c-dev)

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