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Restore old logic, to reinstate working XT.

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Thomas Harte
2025-09-11 22:47:26 -04:00
parent 035713b4d3
commit fb8e8b4b3a
1 changed files with 19 additions and 6 deletions
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Machines/PCCompatible/PIC.hpp
+19 -6
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@@ -122,16 +122,29 @@ public:
template <int input>
void apply_edge(const bool final_level) {
static constexpr uint8_t input_mask = 1 << input;
const auto old_levels = levels_;
const uint8_t new_bit = final_level ? input_mask : 0;
levels_ = (levels_ & ~input_mask) | new_bit;
// Guess: level triggered means the request can be forwarded only so long as the
// relevant input is actually high. Whereas edge triggered implies capturing state.
if(level_triggered_) {
requests_ = levels_;
} else {
requests_ |= (levels_ ^ old_levels) & new_bit;
requests_ &= ~input_mask;
}
requests_ |= new_bit;
// TODO: I don't think the above is correct because it defines an edge trigger to be any time that the
// level is redeclared as 1 but a previous request has been satisfied. So that's not about watching the rising
// edge of the input as it should be.
//
// ... but the code as below causes my XT to fail to boot. So it's possibly incorrect too, in some other way,
// or else it trigger a latent piece of incorrect behaviour elsewhere.
// const auto old_levels = levels_;
// levels_ = (levels_ & ~input_mask) | new_bit;
//
// if(level_triggered_) {
// requests_ = (requests_ & ~input_mask) | new_bit;
// } else {
// requests_ |= (levels_ ^ old_levels) & new_bit;
// }
Log::info().append("%d to %d => requests now %02x", input, final_level, requests_);
}