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Adds a type for the operation bitfield.

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Thomas Harte 2021-07-18 20:54:54 -04:00
parent 3e2bac8129
commit b2ae8e7a4a
1 changed files with 21 additions and 15 deletions
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36
Processors/68000/68000.hpp
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@ -49,51 +49,53 @@ namespace MC68000 {
avoid the runtime cost of actual DTack emulation. But such as the bus allows.)
*/
struct Microcycle {
using OperationT = unsigned int;
/// Indicates that the address strobe and exactly one of the data strobes are active; you can determine
/// which by inspecting the low bit of the provided address. The RW line indicates a read.
static constexpr int SelectByte = 1 << 0;
static constexpr OperationT SelectByte = 1 << 0;
// Maintenance note: this is bit 0 to reduce the cost of getting a host-endian
// bytewise address. The assumption that it is bit 0 is also used for branchless
// selection in a few places. See implementation of host_endian_byte_address(),
// value8_high(), value8_low() and value16().
/// Indicates that the address and both data select strobes are active.
static constexpr int SelectWord = 1 << 1;
static constexpr OperationT SelectWord = 1 << 1;
/// A NewAddress cycle is one in which the address strobe is initially low but becomes high;
/// this correlates to states 0 to 5 of a standard read/write cycle.
static constexpr int NewAddress = 1 << 2;
static constexpr OperationT NewAddress = 1 << 2;
/// A SameAddress cycle is one in which the address strobe is continuously asserted, but neither
/// of the data strobes are.
static constexpr int SameAddress = 1 << 3;
static constexpr OperationT SameAddress = 1 << 3;
/// A Reset cycle is one in which the RESET output is asserted.
static constexpr int Reset = 1 << 4;
static constexpr OperationT Reset = 1 << 4;
/// If set, indicates a read. Otherwise, a write.
static constexpr int Read = 1 << 5;
static constexpr OperationT Read = 1 << 5;
/// Contains the value of line FC0 if it is not implicit via InterruptAcknowledge.
static constexpr int IsData = 1 << 6;
static constexpr OperationT IsData = 1 << 6;
/// Contains the value of line FC1 if it is not implicit via InterruptAcknowledge.
static constexpr int IsProgram = 1 << 7;
static constexpr OperationT IsProgram = 1 << 7;
/// The interrupt acknowledge cycle is that during which the 68000 seeks to obtain the vector for
/// an interrupt it plans to observe. Noted on a real 68000 by all FCs being set to 1.
static constexpr int InterruptAcknowledge = 1 << 8;
static constexpr OperationT InterruptAcknowledge = 1 << 8;
/// Represents the state of the 68000's valid memory address line — indicating whether this microcycle
/// is synchronised with the E clock to satisfy a valid peripheral address request.
static constexpr int IsPeripheral = 1 << 9;
static constexpr OperationT IsPeripheral = 1 << 9;
/// Provides the 68000's bus grant line — indicating whether a bus request has been acknowledged.
static constexpr int BusGrant = 1 << 10;
static constexpr OperationT BusGrant = 1 << 10;
/// Contains a valid combination of the various static constexpr int flags, describing the operation
/// performed by this Microcycle.
unsigned int operation = 0;
OperationT operation = 0;
/// Describes the duration of this Microcycle.
HalfCycles length = HalfCycles(4);
@ -289,8 +291,8 @@ struct Microcycle {
return ((*address) & 0x00fffffe) >> 1;
}
static constexpr int PermitRead = (1 << 11);
static constexpr int PermitWrite = (1 << 12);
static constexpr OperationT PermitRead = (1 << 11);
static constexpr OperationT PermitWrite = (1 << 12);
/*!
Assuming this to be a cycle with a data select active, applies it to @c target
@ -300,21 +302,25 @@ struct Microcycle {
* if this is a word read, reads a word (in the host platform's endianness) from @c target; and
* if this is a write, does the converse of a read.
*/
forceinline void apply(uint8_t *target, int read_write_mask = PermitRead | PermitWrite) const {
forceinline void apply(uint8_t *target, OperationT read_write_mask = PermitRead | PermitWrite) const {
switch((operation | read_write_mask) & (SelectWord | SelectByte | Read | PermitRead | PermitWrite)) {
default:
break;
case SelectWord | Read | PermitRead:
case SelectWord | Read | PermitRead | PermitWrite:
value->full = *reinterpret_cast<uint16_t *>(target);
break;
case SelectByte | Read | PermitRead:
case SelectByte | Read | PermitRead | PermitWrite:
value->halves.low = *target;
break;
case SelectWord | PermitWrite:
case SelectWord | PermitWrite | PermitRead:
*reinterpret_cast<uint16_t *>(target) = value->full;
break;
case SelectByte | PermitWrite:
case SelectByte | PermitWrite | PermitRead:
*target = value->halves.low;
break;
}