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ncr53c90: better guess at sequence logic for macqd700

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This commit is contained in:
Patrick Mackinlay 2023-02-03 12:02:06 +07:00
parent 11d04180ca
commit 0158cdeab6
1 changed files with 5 additions and 1 deletions
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6
src/devices/machine/ncr53c90.cpp
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@ -446,6 +446,10 @@ void ncr53c90_device::step(bool timeout)
case DISC_SEL_ARBITRATION_INIT: case DISC_SEL_ARBITRATION_INIT:
// wait until a command is in the fifo // wait until a command is in the fifo
if (!fifo_pos) { if (!fifo_pos) {
// this sequence isn't documented for initiator selection, but
// it makes macqd700 happy and may be consistent with target
// selection sequences
seq = 1;
// dma starts after bus arbitration/selection is complete // dma starts after bus arbitration/selection is complete
check_drq(); check_drq();
break; break;
@ -1069,7 +1073,7 @@ void ncr53c90_device::timeout_w(uint8_t data)
uint8_t ncr53c90_device::seq_step_r() uint8_t ncr53c90_device::seq_step_r()
{ {
LOG("seq_step_r %d (%s)\n", seq, machine().describe_context()); LOG("seq_step_r %d (%s)\n", seq, machine().describe_context());
return seq + 1; // HACK for Mac Quadra 700; our sequence steps don't correspond exactly to what the real chip does return seq;
} }
void ncr53c90_device::sync_period_w(uint8_t data) void ncr53c90_device::sync_period_w(uint8_t data)