Passing arrayref to C

[Mike Jones]

Suppose I have:

%{^

uint8 funA(uint8* data) { return(0); } // Some array operation happens in here

uint8_t data[256]; // Some place to hold data for funA to work with

%}

// A macro to access the data as an arrayref

macdef my_data =

  $extval(arrayref(uint8, 256),"data")

// And ATS version of the function

fun funA_ (cPtr0(uint8)) : uint8   = "mac#funA"

val v = funA_(ptr2cptr(my_data)) // The compiler does not like this

// Get a value for use

val v' = my_data[0]

Given above, ptr2cptr does not work on the array ref. What is the proper way to pass my_data into the C call?

The assumption here is that funA will never go beyond 256 values into the passed in data. This is because of a hardware limitation where a count is a byte. So it is safe. So if ATS deals with arrayref(uint8, 256), things can't get into trouble. But I need to pass the ATS array into C to get something in hardware done.

A secondary question.

fun funB(val: arrayref(uint8,256)):uint8 =

val v = funB(my_data)

Is this the proper way to define a function that takes the arrayref? Or is there some signature with and '&' that does this like for a var?

[Hongwei Xi]

Why funA_ is not given the following type instead:

fun funA_ : arrayref(uint8, 256) -> uint8

>>val v = funA_(ptr2cptr(my_data)) // The compiler does not like this

ptr2cptr takes pointer but my_data is an arrayref.

>>fun funB(val: arrayref(uint8,256)):uint8 =

Yes. 'val' is a keyword and should probably be replaced.

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[Hongwei Xi]

By the way, I would like to suggest a different style, which you
may try later when you become more comfortable with ATS.

When I see:

uint8_t data[256];

my immediate reflex is that I can now have the following two functions:

fun{} data_get_at : natLt(256) -> uint8

fun{} data_set_at : (natLt(256), uint8) -> void

If 'data' is read-only, then 'data_set_at' is not available. Also, 'data' can be

shared among threads if that is what you want.

If you really need to call 'funA' in ATS, you can do

val () = $extfcall(void, "funA", $extval(ptr, "data"))

On Tue, Nov 17, 2015 at 8:04 PM, Mike Jones <proc...@gmail.com> wrote:

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[Mike Jones]

Are you saying the following below would work? That by defining funA_ with an array ref a pointer would be passed to the C version funA?

%{^

uint8 funA(uint8* data) { return(0); } // Some array operation happens in here

uint8_t data[256]; // Some place to hold data for funA to work with

%}

fun funA_ (arrayref(uint8, 256) : uint8   = "mac#funA"

[Hongwei Xi]

It should work.

By the way, you could just use the name 'funA' for 'funA_'.

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[Mike Jones]

I only used different names to make the example clear.

I'm having difficulty getting it to compile, so here is the exact code:

fun i2c_stop                           (arrayref(uint8, 256))                : uint8   = "mac#i2c_stop"

%{^

uint8_t i2c_data[256];

%}

macdef i2c_data =

  $extval(arrayref(uint8, 256),"i2c_data")

implement i2c_read_byte(address: uint8): (uint8, uint8) = let

  var b: uint8 = u8(0)

  var err: uint8 =                            err (0, u8)

  val () = ifnerr(i2c_start(),                err, 1, u8)

  val () = ifnerr(i2c_write(wa address),      err, 2, u8)

  val () = ifnerr(i2c_read(),                 err, 3, u8)

  val () = ifnerr(i2c_stop(i2c_data),         err, 4, u8)

  in (err, i2c_data[0]) end

I'm getting errors like:

/*

emit_instr: loc0 = /opt/ATS/ATS2-Postiats-0.2.4/prelude/DATS/array.dats: 1971(line=63, offs=45) -- 1989(line=63, offs=63)

*/

ATSINSmove(tmpret33__1, PMVtmpltcstmat[0](ptr0_get<S2Eapp(S2Ecst(g0uint_t0ype); S2Eextkind(atstype_uint8))>)(tmp34__1)) ;

DATS/smbus_dats.c:1036:43: error: 'ptr0_get' undeclared (first use in this function)

 ATSINSmove(tmpret33__1, PMVtmpltcstmat[0](ptr0_get<S2Eapp(S2Ecst(g0uint_t0ype); S2Eextkind(atstype_uint8))>)(tmp34__1)) ;

DATS/smbus_dats.c:1036:66: error: 'g0uint_t0ype' undeclared (first use in this function)

 ATSINSmove(tmpret33__1, PMVtmpltcstmat[0](ptr0_get<S2Eapp(S2Ecst(g0uint_t0ype); S2Eextkind(atstype_uint8))>)(tmp34__1)) ;

[Hongwei Xi]

It seems that you need the following line:

staload _ = "prelude/DATS/unsafe.dats"

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[Mike Jones]

I had this:

   staload "prelude/SATS/unsafe.sats"

But this works when added:

   staload _ = "prelude/DATS/unsafe.dats"

[Hongwei Xi]

ptr0_get is a template whose definition is in unsafe.dats.

So you need to staload unsafe.dats (not just unsafe.sats).

Otherwise, the compiler would not be able to compile ptr0_get
(and you saw error messages saying something about PMVtmpltcstmat[0])

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[Mike Jones]

Ok, I see now.

So now I have:

implement i2c_read_byte(address: uint8): (uint8, uint8) = let

How do I export this so that C can call it?

I saw from the book that the tuple becomes a struct. But it did not cover how to make the function. Is there some example of how to do this?

[Hongwei Xi]

This can be done but it is a bit tricky.

Usually, such a function is given the following interface:

fun i2c_read_byte
  (address: uint8, byte1: &uint8 >> _, byte2: &uint8 >> _): void

Also, how about the following interface:

fun i2c_read_byte(address: uint8): uint16

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[Mike Jones]

Note, calling this from C is silly, but I want to test before I wrap a whole state machine around it. Even so, eventually, even that has to be called from C. So the need is general.

[gmhwxi]

The following line cause a type of the name 'uint8_pair_t'
to be defined in the generated C code:

extern typedef "uint8_pair_t" = (uint8, uint8)

So the interface for i2c_read_byte in C is

extern
uint8_pair_t i2c_read_byte (uint8_t address) ;

[Mike Jones]

Ok, let's start with a simpler one:

fun i2c_write_byte_data                (uint8, uint8, uint8)                 : uint8

implement i2c_read_byte_data(address: uint8, command: uint8): (uint8, uint8) = let

This generated:

/*

local: wa_0$0(level=0)

global: wa_0$0(level=0), i2c_write_byte_data$54$0(level=0)

local: 

global: 

*/

ATSextern()

atstkind_t0ype(atstype_uint8)

_057_home_057_mike_057_cypress_057_workspace_057_UsbI2cRegMode_057_SATS_057_smbus_056_sats__i2c_write_byte_data(atstkind_t0ype(atstype_uint8) arg0, atstkind_t0ype(atstype_uint8) arg1, atstkind_t0ype(atstype_uint8) arg2)

{

I then call it like this:

extern uint8_t _057_home_057_mike_057_cypress_057_workspace_057_UsbI2cRegMode_057_SATS_057_smbus_056_sats__i2c_write_byte_data(uint8_t arg0, uint8_t arg1, uint8_t arg2);

uint8_t v = _057_home_057_mike_057_cypress_057_workspace_057_UsbI2cRegMode_057_SATS_057_smbus_056_sats__i2c_write_byte_data(0x00, 0x00, 0x00);

And it compiles. But what is a good way to deal with this long prefix? All I can think of is to wrap a macro around it like:

#define i2c_write_byte_data _057_home_057_mike_057_cypress_057_workspace_057_UsbI2cRegMode_057_SATS_057_smbus_056_sats__i2c_write_byte_data

But this will result in messy compiler errors.

[gmhwxi]

This issue is mention in Chapter 8 of the Intro-to-ATS book:

http://ats-lang.sourceforge.net/DOCUMENT/INT2PROGINATS/HTML/HTMLTOC/c2005.html

extern
fun i2c_write_byte_data (...): .. = "ext#whatever_name_you_like_in_c_for_this_function"

[Mike Jones]

Oh, I was reading after that point and missed that paragraph. I'll test now and confirm the array ref passes a pointer, etc.

[Mike Jones]

The compiler seems to generate the _c names for the write, but not the read. Looks like the compiler can't handled the struct return and just ignores the ext def.

fun i2c_read_byte_data                 (uint8, uint8)                        : (uint8, uint8) = "ext#i2c_read_byte_data_c"

fun i2c_write_byte_data                (uint8, uint8, uint8)                 : uint8 = "ext#i2c_write_byte_data_c"

fun i2c_read_word_data                 (uint8, uint8)                        : (uint8, uint16) = "ext#i2c_read_word_data_c"

fun i2c_write_word_data                (uint8, uint8, uint16)                : uint8 = "ext#i2c_write_word_data_c"

[Hongwei Xi]

If i2c_read_byte_data is implemented, then the compiler should generate i2c_read_byte_data_c.

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[Mike Jones]

I think there may have been a problem with my make. After a make clean, it showed up.

[Mike Jones]

Ok, I'm closer. Compiles. Runs. But having some problem with return values.

In ATS:

%{^

uint8_t i2c_data[256];

%}

macdef i2c_data =

  $extval(arrayref(uint8, 256),"i2c_data")

fun i2c_read_byte_data                 (uint8, uint8)                        : (uint8, uint8) = "ext#i2c_read_byte_data_c"

implement i2c_read_byte(address: uint8): (uint8, uint8) = let

  var err: uint8 =                            err (0, u8)

  val () = ifnerr(i2c_start(),                err, 1, u8)

  val () = ifnerr(i2c_write(wa address),      err, 2, u8)

  val () = ifnerr(i2c_repeated_start(),       err, 3, u8)

  val () = ifnerr(i2c_read(),                 err, 4, u8)

  val () = ifnerr(i2c_stop(i2c_data),         err, 5, u8)

  in (err, i2c_data[0]) end

In C, supporting i2c_stop(i2c_data) above in ATS:

uint8_t i2c_stop(uint8_t *data)

{

CyU3PReturnStatus_t status = CY_U3P_SUCCESS;

CyU3PDebugPrint (2, "I2C Stop\r\n");

if (read)

{

status = CyU3PI2cReceiveBytes (&shared_preamble, shared_data, shared_data_len, 0);

memcpy(data, shared_data, shared_data_len);

}

else

{

if (shared_data_len == 0)

shared_data[shared_data_len++] = shared_preamble.buffer[--shared_preamble.length];

status = CyU3PI2cTransmitBytes (&shared_preamble, shared_data, shared_data_len, 0);

}

return((uint8_t)status);

}

In C application code:

typedef

struct {

uint8_t err;

uint16_t byte;

} err_byte;

extern err_byte i2c_read_byte_data_c(uint8_t, uint8_t);

    err_byte sb;

    uint8_t b; 

    sb = i2c_read_byte_data_c(0x30, 0x00);

    status = sb.err;

    b = sb.byte;

In the debugger while stopped inside i2c_stop() (C code), I look at i2c_data and see that it is set to 0x01. But what is returned to the err_byte struct is a 0x00.

This implies that in the ATS, the code in (err, i2c_data[0]) end is failing to index into the C array i2c_data, or the mapping to the returned struct is failing. Is there some problem with my C declaration of the struct? Could there be a memory alignment issue requiring some forced packing or something?

Note this is a 32 bit ARM 9. And I am not using the C99 option during compilation, I'm using whatever the default is for the Cypress make system.

[Mike Jones]

Yep, was packing. This fixed it.

#pragma pack(push, 1)

typedef

struct {

uint8_t err;

uint16_t word;

} err_word;

#pragma pack(pop)

[gmhwxi]

Interesting :)

[Mike Jones]

Yep. I have a ThreadX app thread in the Cypress FX3 USB3 device calling ATS, which is then calling back into C to operate the I2C bus. Now I can write a whole application in ATS. Given the level or reliability required for a USB Device, this will be a big win.