mirror of
https://github.com/TomHarte/CLK.git
synced 2024-07-04 18:29:40 +00:00
Start arrangements for full extension words.
This commit is contained in:
parent
3f3c9f7491
commit
95c526d957
@ -201,14 +201,31 @@ template <typename IntT> IntT Executor<model, BusHandler>::State::read_pc() {
|
||||
|
||||
template <Model model, typename BusHandler>
|
||||
uint32_t Executor<model, BusHandler>::State::index_8bitdisplacement() {
|
||||
// TODO: if not a 68000, check bit 8 for whether this should be a full extension word;
|
||||
// also include the scale field even if not.
|
||||
// Get the brief extension word.
|
||||
const auto extension = read_pc<uint16_t>();
|
||||
|
||||
// The 68000, 68080 and 68010 do not support the scale field, and are limited
|
||||
// to brief extension words.
|
||||
const int scale = model <= Model::M68010 ? 0 : (extension >> 9) & 3;
|
||||
|
||||
// Decode brief instruction word fields.
|
||||
const auto offset = int8_t(extension);
|
||||
const int register_index = (extension >> 12) & 15;
|
||||
const uint32_t displacement = registers[register_index].l;
|
||||
const uint32_t sized_displacement = (extension & 0x800) ? displacement : int16_t(displacement);
|
||||
return offset + sized_displacement;
|
||||
|
||||
// The 68000, 68080 and 68010 support only brief extension words.
|
||||
if(model <= Model::M68010 || !(extension & 0x100)) {
|
||||
const uint32_t displacement = registers[register_index].l << scale;
|
||||
const uint32_t sized_displacement = (extension & 0x800) ? displacement : int16_t(displacement);
|
||||
return offset + sized_displacement;
|
||||
}
|
||||
|
||||
// Determine a long extension.
|
||||
//
|
||||
// Cf. https://edwardhalferty.com/2020/12/16/decoding-the-extended-addressing-modes-of-the-68000/
|
||||
// const bool has_base = extension & 0x80;
|
||||
// const bool has_index = extension & 0x40;
|
||||
|
||||
return 0;
|
||||
}
|
||||
|
||||
template <Model model, typename BusHandler>
|
||||
|
Loading…
Reference in New Issue
Block a user