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cxxrtl: add a C API for driving and introspecting designs.

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Compared to the C++ API, the C API currently has two limitations:
  1. Memories cannot be updated in a race-free way.
  2. Black boxes cannot be implemented in C.
This commit is contained in:
whitequark 2020-06-05 13:52:30 +00:00
parent f6e16e7f4c
commit c399359ed6
4 changed files with 291 additions and 29 deletions
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75
backends/cxxrtl/cxxrtl.h
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@ -33,13 +33,15 @@
#include <memory>
#include <sstream>
// The cxxrtl support library implements compile time specialized arbitrary width arithmetics, as well as provides
#include <backends/cxxrtl/cxxrtl_capi.h>
// The CXXRTL support library implements compile time specialized arbitrary width arithmetics, as well as provides
// composite lvalues made out of bit slices and concatenations of lvalues. This allows the `write_cxxrtl` pass
// to perform a straightforward translation of RTLIL structures to readable C++, relying on the C++ compiler
// to unwrap the abstraction and generate efficient code.
namespace cxxrtl {
// All arbitrary-width values in cxxrtl are backed by arrays of unsigned integers called chunks. The chunk size
// All arbitrary-width values in CXXRTL are backed by arrays of unsigned integers called chunks. The chunk size
// is the same regardless of the value width to simplify manipulating values via FFI interfaces, e.g. driving
// and introspecting the simulation in Python.
//
@ -716,39 +718,49 @@ typedef std::map<std::string, metadata> metadata_map;
// This structure is intended for consumption via foreign function interfaces, like Python's ctypes.
// Because of this it uses a C-style layout that is easy to parse rather than more idiomatic C++.
struct debug_item {
//
// To avoid violating strict aliasing rules, this structure has to be a subclass of the one used
// in the C API, or it would not be possible to cast between the pointers to these.
struct debug_item : ::cxxrtl_object {
enum : uint32_t {
VALUE = 0,
WIRE = 1,
MEMORY = 2,
} type;
size_t width; // in bits
size_t depth; // 1 if `type != MEMORY`
chunk_t *curr;
chunk_t *next; // nullptr if `type == VALUE || type == MEMORY`
VALUE = CXXRTL_VALUE,
WIRE = CXXRTL_WIRE,
MEMORY = CXXRTL_MEMORY,
};
template<size_t Bits>
debug_item(value<Bits> &item) : type(VALUE), width(Bits), depth(1),
curr(item.data), next(nullptr) {
static_assert(sizeof(item) == value<Bits>::chunks * sizeof(chunk_t),
"value<Bits> is not compatible with C layout");
}
debug_item(value<Bits> &item) {
static_assert(sizeof(item) == value<Bits>::chunks * sizeof(chunk_t),
"value<Bits> is not compatible with C layout");
type = VALUE;
width = Bits;
depth = 1;
curr = item.data;
next = item.data;
}
template<size_t Bits>
debug_item(wire<Bits> &item) : type(WIRE), width(Bits), depth(1),
curr(item.curr.data), next(item.next.data) {
static_assert(sizeof(item.curr) == value<Bits>::chunks * sizeof(chunk_t) &&
sizeof(item.next) == value<Bits>::chunks * sizeof(chunk_t),
"wire<Bits> is not compatible with C layout");
}
debug_item(wire<Bits> &item) {
static_assert(sizeof(item.curr) == value<Bits>::chunks * sizeof(chunk_t) &&
sizeof(item.next) == value<Bits>::chunks * sizeof(chunk_t),
"wire<Bits> is not compatible with C layout");
type = WIRE;
width = Bits;
depth = 1;
curr = item.curr.data;
next = item.next.data;
}
template<size_t Width>
debug_item(memory<Width> &item) : type(MEMORY), width(Width), depth(item.data.size()),
curr(item.data.empty() ? nullptr : item.data[0].data), next(nullptr) {
static_assert(sizeof(item.data[0]) == value<Width>::chunks * sizeof(chunk_t),
"memory<Width> is not compatible with C layout");
}
debug_item(memory<Width> &item) {
static_assert(sizeof(item.data[0]) == value<Width>::chunks * sizeof(chunk_t),
"memory<Width> is not compatible with C layout");
type = MEMORY;
width = Width;
depth = item.data.size();
curr = item.data.empty() ? nullptr : item.data[0].data;
next = nullptr;
}
};
static_assert(std::is_standard_layout<debug_item>::value, "debug_item is not compatible with C layout");
@ -779,7 +791,12 @@ struct module {
} // namespace cxxrtl
// Definitions of internal Yosys cells. Other than the functions in this namespace, cxxrtl is fully generic
// Internal structure used to communicate with the implementation of the C interface.
typedef struct _cxxrtl_toplevel {
std::unique_ptr<cxxrtl::module> module;
} *cxxrtl_toplevel;
// Definitions of internal Yosys cells. Other than the functions in this namespace, CXXRTL is fully generic
// and indepenent of Yosys implementation details.
//
// The `write_cxxrtl` pass translates internal cells (cells with names that start with `$`) to calls of these