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Merge pull request #695 from TomHarte/68000ByteAccess

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Corrects 16-bit view of the 68000 bus during 8-bit operations.
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Thomas Harte 2019-12-21 21:08:39 -05:00 committed by GitHub
commit 25da5ebdae
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1 changed files with 9 additions and 14 deletions
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23
Processors/68000/68000.hpp
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@ -53,7 +53,9 @@ struct Microcycle {
/// which by inspecting the low bit of the provided address. The RW line indicates a read.
static const int SelectByte = 1 << 0;
// Maintenance note: this is bit 0 to reduce the cost of getting a host-endian
// bytewise address. See implementation of host_endian_byte_address().
// 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 const int SelectWord = 1 << 1;
@ -223,9 +225,8 @@ struct Microcycle {
this is a write cycle.
*/
forceinline uint16_t value16() const {
if(operation & SelectWord) return value->full;
const auto shift = byte_shift();
return uint16_t((value->halves.low << shift) | (0xff00 >> shift));
const uint16_t values[] = { value->full, uint16_t((value->halves.low << 8) | value->halves.low) };
return values[operation & SelectByte];
}
/*!
@ -233,11 +234,8 @@ struct Microcycle {
@c 0xff otherwise. Assumes this is a write cycle.
*/
forceinline uint8_t value8_high() const {
if(operation & SelectWord) {
return uint8_t(value->full >> 8);
}
return uint8_t(value->halves.low | (0xff00 >> ((*address & 1) << 3)));
const uint8_t values[] = { uint8_t(value->full >> 8), value->halves.low};
return values[operation & SelectByte];
}
/*!
@ -245,11 +243,8 @@ struct Microcycle {
@c 0xff otherwise. Assumes this is a write cycle.
*/
forceinline uint8_t value8_low() const {
if(operation & SelectWord) {
return uint8_t(value->full);
}
return uint8_t(value->halves.low | (0x00ff << ((*address & 1) << 3)));
const uint8_t values[] = { uint8_t(value->full), value->halves.low};
return values[operation & SelectByte];
}
/*!