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Tries to add semantic meaning to the various auxiliary control fields.

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To consider: decoding at set?
This commit is contained in:
Thomas Harte 2020-09-22 20:50:39 -04:00
parent 41f69405d8
commit 022ec20e75
2 changed files with 34 additions and 16 deletions
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28
Components/6522/Implementation/6522Implementation.hpp
View File

@ -86,7 +86,7 @@ template <typename T> void MOS6522<T>::write(int address, uint8_t value) {
timer_is_running_[0] = true;
// If PB7 output mode is active, set it low.
if(registers_.auxiliary_control & 0x80) {
if(timer1_is_controlling_pb7()) {
registers_.timer_port_b_output &= 0x7f;
evaluate_port_b_output();
}
@ -120,9 +120,11 @@ template <typename T> void MOS6522<T>::write(int address, uint8_t value) {
registers_.auxiliary_control = value;
evaluate_cb2_output();
printf("Shift mode: %d\n", shift_mode());
// This is a bit of a guess: reset the timer-based PB7 output to its default high level
// any timer that timer-linked PB7 output is disabled.
if(!(registers_.auxiliary_control & 0x80)) {
if(!timer1_is_controlling_pb7()) {
registers_.timer_port_b_output |= 0x80;
}
evaluate_port_b_output();
@ -304,16 +306,13 @@ template <typename T> void MOS6522<T>::do_phase2() {
registers_.timer_needs_reload = false;
registers_.timer[0] = registers_.timer_latch[0];
} else {
// Decrement timer 1 based on clock if enabled.
if(!(registers_.auxiliary_control & 0x20)) {
-- registers_.timer[0];
}
-- registers_.timer[0];
}
// Count down timer 2 if it is in timed interrupt mode (i.e. auxiliary control bit 5 is clear).
// TODO: implement count down on PB6 if this bit isn't set.
registers_.timer[1] -= 1 ^ ((registers_.auxiliary_control >> 5)&1);
registers_.timer[1] -= timer2_clock_decrement();
// TODO: can eliminate conditional branches here.
if(registers_.next_timer[0] >= 0) {
registers_.timer[0] = uint16_t(registers_.next_timer[0]);
registers_.next_timer[0] = -1;
@ -364,13 +363,13 @@ template <typename T> void MOS6522<T>::do_phase1() {
reevaluate_interrupts();
// Determine whether to reload.
if(registers_.auxiliary_control&0x40)
if(timer1_is_continuous())
registers_.timer_needs_reload = true;
else
timer_is_running_[0] = false;
// Determine whether to toggle PB7.
if(registers_.auxiliary_control&0x80) {
if(timer1_is_controlling_pb7()) {
registers_.timer_port_b_output ^= 0x80;
bus_handler_.run_for(time_since_bus_handler_call_.flush<HalfCycles>());
evaluate_port_b_output();
@ -481,10 +480,11 @@ template <typename T> void MOS6522<T>::shift_in() {
}
template <typename T> void MOS6522<T>::shift_out() {
// When shifting out, the shift register rotates rather than strictly shifts.
// TODO: is that true for all modes?
if(shift_mode() == ShiftMode::OutUnderT2FreeRunning || shift_bits_remaining_) {
registers_.shift = uint8_t((registers_.shift << 1) | (registers_.shift >> 7));
const bool is_free_running = shift_mode() == ShiftMode::OutUnderT2FreeRunning;
if(is_free_running || shift_bits_remaining_) {
// Recirculate bits only if in free-running mode (?)
const uint8_t incoming_bit = (registers_.shift >> 7) * is_free_running;
registers_.shift = uint8_t(registers_.shift << 1) | incoming_bit;
evaluate_cb2_output();
--shift_bits_remaining_;

22
Components/6522/Implementation/6522Storage.hpp
View File

@ -81,12 +81,30 @@ class MOS6522Storage {
OutUnderPhase2 = 6,
OutUnderCB1 = 7
};
ShiftMode shift_mode() const {
return ShiftMode((registers_.auxiliary_control >> 2) & 7);
bool timer1_is_controlling_pb7() const {
return registers_.auxiliary_control & 0x80;
}
bool timer1_is_continuous() const {
return registers_.auxiliary_control & 0x40;
}
bool is_shifting_out() const {
return registers_.auxiliary_control & 0x10;
}
int timer2_clock_decrement() const {
return 1 ^ ((registers_.auxiliary_control >> 5)&1);
}
int timer2_pb6_decrement() const {
return (registers_.auxiliary_control >> 5)&1;
}
ShiftMode shift_mode() const {
return ShiftMode((registers_.auxiliary_control >> 2) & 7);
}
bool portb_is_latched() const {
return registers_.auxiliary_control & 0x02;
}
bool port1_is_latched() const {
return registers_.auxiliary_control & 0x01;
}
};
}