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Yamaha: don't touch address at all unless a RAM access.

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This commit is contained in:
Thomas Harte 2023-02-11 22:43:29 -05:00
parent 8768ee1504
commit 914a9e0c84
1 changed files with 11 additions and 6 deletions
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17
Components/9918/Implementation/9918.cpp
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@ -921,21 +921,26 @@ void Base<personality>::write_register(uint8_t value) {
// The RAM pointer is always set on a second write, regardless of
// whether the caller is intending to enqueue a VDP operation.
// If this is a Yamaha VDP then the latched byte isn't set as part
// of the address until now.
// If this isn't a Yamaha VDP then the RAM address is updated
// regardless of whether this turns out to be a register access.
//
// The top two bits are used to determine the type of write; only
// the lower six are actual address.
if constexpr (is_yamaha_vdp(personality)) {
install_field<0>(ram_pointer_, low_write_);
}
if constexpr (!is_yamaha_vdp(personality)) {
install_field<8, 6>(ram_pointer_, value);
}
write_phase_ = false;
if(value & 0x80) {
commit_register(value, low_write_);
} else {
// This is an access via the RAM pointer.
// This is an access via the RAM pointer; if this is a Yamaha VDP then update
// the low 14-bits of the RAM pointer now.
if constexpr (is_yamaha_vdp(personality)) {
install_field<0>(ram_pointer_, low_write_);
install_field<8, 6>(ram_pointer_, value);
}
if(!(value & 0x40)) {
// A read request is enqueued upon setting the address; conversely a write
// won't be enqueued unless and until some actual data is supplied.