diff options
Diffstat (limited to 'backends/cxxrtl/cxxrtl_capi.h')
| -rw-r--r-- | backends/cxxrtl/cxxrtl_capi.h | 72 |
1 files changed, 70 insertions, 2 deletions
diff --git a/backends/cxxrtl/cxxrtl_capi.h b/backends/cxxrtl/cxxrtl_capi.h index 1f1942803..385d6dcf3 100644 --- a/backends/cxxrtl/cxxrtl_capi.h +++ b/backends/cxxrtl/cxxrtl_capi.h @@ -73,6 +73,10 @@ int cxxrtl_commit(cxxrtl_handle handle); 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. @@ -86,7 +90,8 @@ enum cxxrtl_type { 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. + // 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 @@ -103,7 +108,7 @@ enum cxxrtl_type { CXXRTL_MEMORY = 2, // Aliases correspond to netlist nodes driven by another node such that their value is always - // exactly equal, or driven by a constant value. + // exactly equal. // // Aliases can be inspected via the `curr` pointer. They cannot be modified, and the `next` // pointer is always NULL. @@ -112,6 +117,66 @@ enum cxxrtl_type { // 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 @@ -123,6 +188,9 @@ struct cxxrtl_object { // 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; |