Merge pull request #2469 from whitequark/cxxrtl-no-clk

[yosys.git] / backends / cxxrtl / cxxrtl_capi.h

/*
 *  yosys -- Yosys Open SYnthesis Suite
 *
 *  Copyright (C) 2020  whitequark <whitequark@whitequark.org>
 *
 *  Permission to use, copy, modify, and/or distribute this software for any
 *  purpose with or without fee is hereby granted.
 *
 *  THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
 *  WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
 *  MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
 *  ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
 *  WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
 *  ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
 *  OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
 *
 */

#ifndef CXXRTL_CAPI_H
#define CXXRTL_CAPI_H

// This file is a part of the CXXRTL C API. It should be used together with `cxxrtl_capi.cc`.
//
// The CXXRTL C API makes it possible to drive CXXRTL designs using C or any other language that
// supports the C ABI, for example, Python. It does not provide a way to implement black boxes.

#include <stddef.h>
#include <stdint.h>
#include <assert.h>

#ifdef __cplusplus
extern "C" {
#endif

// Opaque reference to a design toplevel.
//
// A design toplevel can only be used to create a design handle.
typedef struct _cxxrtl_toplevel *cxxrtl_toplevel;

// The constructor for a design toplevel is provided as a part of generated code for that design.
// Its prototype matches:
//
// cxxrtl_toplevel <design-name>_create();

// Opaque reference to a design handle.
//
// A design handle is required by all operations in the C API.
typedef struct _cxxrtl_handle *cxxrtl_handle;

// Create a design handle from a design toplevel.
//
// The `design` is consumed by this operation and cannot be used afterwards.
cxxrtl_handle cxxrtl_create(cxxrtl_toplevel design);

// Release all resources used by a design and its handle.
void cxxrtl_destroy(cxxrtl_handle handle);

// Reinitialize the design, replacing the internal state with the reset values while preserving
// black boxes.
//
// This operation is essentially equivalent to a power-on reset. Values, wires, and memories are
// returned to their reset state while preserving the state of black boxes and keeping all of
// the interior pointers obtained with e.g. `cxxrtl_get` valid.
void cxxrtl_reset(cxxrtl_handle handle);

// Evaluate the design, propagating changes on inputs to the `next` value of internal state and
// output wires.
//
// Returns 1 if the design is known to immediately converge, 0 otherwise.
int cxxrtl_eval(cxxrtl_handle handle);

// Commit the design, replacing the `curr` value of internal state and output wires with the `next`
// value.
//
// Return 1 if any of the `curr` values were updated, 0 otherwise.
int cxxrtl_commit(cxxrtl_handle handle);

// Simulate the design to a fixed point.
//
// Returns the number of delta cycles.
size_t cxxrtl_step(cxxrtl_handle handle);

// Type of a simulated object.
//
// The type of a simulated object indicates the way it is stored and the operations that are legal
// to perform on it (i.e. won't crash the simulation). It says very little about object semantics,
// which is specified through flags.
enum cxxrtl_type {
        // Values correspond to singly buffered netlist nodes, i.e. nodes driven exclusively by
        // combinatorial cells, or toplevel input nodes.
        //
        // Values can be inspected via the `curr` pointer. If the `next` pointer is NULL, the value is
        // driven by a constant and can never be modified. Otherwise, the value can be modified through
        // the `next` pointer (which is equal to `curr` if not NULL). Note that changes to the bits
        // driven by combinatorial cells will be ignored.
        //
        // Values always have depth 1.
        CXXRTL_VALUE = 0,

        // Wires correspond to doubly buffered netlist nodes, i.e. nodes driven, at least in part, by
        // storage cells, or by combinatorial cells that are a part of a feedback path. They are also
        // present in non-optimized builds.
        //
        // Wires can be inspected via the `curr` pointer and modified via the `next` pointer (which are
        // distinct for wires). Note that changes to the bits driven by combinatorial cells will be
        // ignored.
        //
        // Wires always have depth 1.
        CXXRTL_WIRE = 1,

        // Memories correspond to memory cells.
        //
        // Memories can be inspected and modified via the `curr` pointer. Due to a limitation of this
        // API, memories cannot yet be modified in a guaranteed race-free way, and the `next` pointer is
        // always NULL.
        CXXRTL_MEMORY = 2,

        // Aliases correspond to netlist nodes driven by another node such that their value is always
        // exactly equal.
        //
        // Aliases can be inspected via the `curr` pointer. They cannot be modified, and the `next`
        // pointer is always NULL.
        CXXRTL_ALIAS = 3,

        // More object types may be added in the future, but the existing ones will never change.
};

// Flags of a simulated object.
//
// The flags of a simulated object indicate its role in the netlist:
//  * The flags `CXXRTL_INPUT` and `CXXRTL_OUTPUT` designate module ports.
//  * The flags `CXXRTL_DRIVEN_SYNC`, `CXXRTL_DRIVEN_COMB`, and `CXXRTL_UNDRIVEN` specify
//    the semantics of node state. An object with several of these flags set has different bits
//    follow different semantics.
enum cxxrtl_flag {
        // Node is a module input port.
        //
        // This flag can be set on objects of type `CXXRTL_VALUE` and `CXXRTL_WIRE`. It may be combined
        // with `CXXRTL_OUTPUT`, as well as other flags.
        CXXRTL_INPUT = 1 << 0,

        // Node is a module output port.
        //
        // This flag can be set on objects of type `CXXRTL_WIRE`. It may be combined with `CXXRTL_INPUT`,
        // as well as other flags.
        CXXRTL_OUTPUT = 1 << 1,

        // Node is a module inout port.
        //
        // This flag can be set on objects of type `CXXRTL_WIRE`. It may be combined with other flags.
        CXXRTL_INOUT = (CXXRTL_INPUT|CXXRTL_OUTPUT),

        // Node has bits that are driven by a storage cell.
        //
        // This flag can be set on objects of type `CXXRTL_WIRE`. It may be combined with
        // `CXXRTL_DRIVEN_COMB` and `CXXRTL_UNDRIVEN`, as well as other flags.
        //
        // This flag is set on wires that have bits connected directly to the output of a flip-flop or
        // a latch, and hold its state. Many `CXXRTL_WIRE` objects may not have the `CXXRTL_DRIVEN_SYNC`
        // flag set; for example, output ports and feedback wires generally won't. Writing to the `next`
        // pointer of these wires updates stored state, and for designs without combinatorial loops,
        // capturing the value from every of these wires through the `curr` pointer creates a complete
        // snapshot of the design state.
        CXXRTL_DRIVEN_SYNC = 1 << 2,

        // Node has bits that are driven by a combinatorial cell or another node.
        //
        // This flag can be set on objects of type `CXXRTL_VALUE` and `CXXRTL_WIRE`. It may be combined
        // with `CXXRTL_DRIVEN_SYNC` and `CXXRTL_UNDRIVEN`, as well as other flags.
        //
        // This flag is set on objects that have bits connected to the output of a combinatorial cell,
        // or directly to another node. For designs without combinatorial loops, writing to such bits
        // through the `next` pointer (if it is not NULL) has no effect.
        CXXRTL_DRIVEN_COMB = 1 << 3,

        // Node has bits that are not driven.
        //
        // This flag can be set on objects of type `CXXRTL_VALUE` and `CXXRTL_WIRE`. It may be combined
        // with `CXXRTL_DRIVEN_SYNC` and `CXXRTL_DRIVEN_COMB`, as well as other flags.
        //
        // This flag is set on objects that have bits not driven by an output of any cell or by another
        // node, such as inputs and dangling wires.
        CXXRTL_UNDRIVEN = 1 << 4,

        // More object flags may be added in the future, but the existing ones will never change.
};

// Description of a simulated object.
//
// The `data` array can be accessed directly to inspect and, if applicable, modify the bits
// stored in the object.
struct cxxrtl_object {
        // Type of the object.
        //
        // All objects have the same memory layout determined by `width` and `depth`, but the type
        // determines all other properties of the object.
        uint32_t type; // actually `enum cxxrtl_type`

        // Flags of the object.
        uint32_t flags; // actually bit mask of `enum cxxrtl_flags`

        // Width of the object in bits.
        size_t width;

        // Index of the least significant bit.
        size_t lsb_at;

        // Depth of the object. Only meaningful for memories; for other objects, always 1.
        size_t depth;

        // Index of the first word. Only meaningful for memories; for other objects, always 0;
        size_t zero_at;

        // Bits stored in the object, as 32-bit chunks, least significant bits first.
        //
        // The width is rounded up to a multiple of 32; the padding bits are always set to 0 by
        // the simulation code, and must be always written as 0 when modified by user code.
        // In memories, every element is stored contiguously. Therefore, the total number of chunks
        // in any object is `((width + 31) / 32) * depth`.
        //
        // To allow the simulation to be partitioned into multiple independent units communicating
        // through wires, the bits are double buffered. To avoid race conditions, user code should
        // always read from `curr` and write to `next`. The `curr` pointer is always valid; for objects
        // that cannot be modified, or cannot be modified in a race-free way, `next` is NULL.
        uint32_t *curr;
        uint32_t *next;

        // More description fields may be added in the future, but the existing ones will never change.
};

// Retrieve description of a simulated object.
//
// The `name` is the full hierarchical name of the object in the Yosys notation, where public names
// have a `\` prefix and hierarchy levels are separated by single spaces. For example, if
// the top-level module instantiates a module `foo`, which in turn contains a wire `bar`, the full
// hierarchical name is `\foo \bar`.
//
// The storage of a single abstract object may be split (usually with the `splitnets` pass) into
// many physical parts, all of which correspond to the same hierarchical name. To handle such cases,
// this function returns an array and writes its length to `parts`. The array is sorted by `lsb_at`.
//
// Returns the object parts if it was found, NULL otherwise. The returned parts are valid until
// the design is destroyed.
struct cxxrtl_object *cxxrtl_get_parts(cxxrtl_handle handle, const char *name, size_t *parts);

// Retrieve description of a single part simulated object.
//
// This function is a shortcut for the most common use of `cxxrtl_get_parts`. It asserts that,
// if the object exists, it consists of a single part. If assertions are disabled, it returns NULL
// for multi-part objects.
inline struct cxxrtl_object *cxxrtl_get(cxxrtl_handle handle, const char *name) {
        size_t parts = 0;
        struct cxxrtl_object *object = cxxrtl_get_parts(handle, name, &parts);
        assert(object == NULL || parts == 1);
        if (object == NULL || parts == 1)
                return object;
        return NULL;
}

// Enumerate simulated objects.
//
// For every object in the simulation, `callback` is called with the provided `data`, the full
// hierarchical name of the object (see `cxxrtl_get` for details), and the object parts.
// The provided `name` and `object` values are valid until the design is destroyed.
void cxxrtl_enum(cxxrtl_handle handle, void *data,
                 void (*callback)(void *data, const char *name,
                                  struct cxxrtl_object *object, size_t parts));

#ifdef __cplusplus
}
#endif

#endif