ata: Implement DMA transfers by mihaip · Pull Request #192 · dingusdev/dingusppc

mihaip · 2026-07-11T22:51:05Z

Add read/write DMA support to ATA devices (mostly reusing existing PIO read and write paths).

We also need to advance data_ptr across DMA pulls so transfers can span multiple DBDMA descriptors.

dingusdev

The implementation of push_data should be its own commit.
Other than that, this looks good.

Implement push_data in AtaBaseDevice using the device transfer buffer and post-transfer callback. Advance the read data pointer across DMA pulls so a transfer can span multiple DBDMA descriptors, and clear the DMA state when transfers finish.

Add read/write DMA command support to ATA hard disks (can mostly reuse the PIO paths).

Also includes the fix from dingusdev/dingusppc#192 which allows the Mac OS X public beta to boot. For #219

Followup to #192. That implemented DMA support, but did not advertise it via the IDENTIFY command. While the 10.0 public beta used it unconditionally, later releases will only use it if the hardware reports the MWDMA bit. Takes booting 10.3 (to WindowServer startup) from ~60 seconds to ~47 seconds on my machine.

With dingusdev#214 we started to advertise the IDE DMA support from dingusdev#192 to guests. That appeared to break booting Mac OS 8.x, at least on the Beige G3: the startup disk was not even detected. Mac OS 8.1 sets up an IDE DMA read as INPUT_MORE, then a NOP with its i field set to always, then STOP, which clears the channel's ACTIVE bit. The emulated transfer completion path interpreted only one following descriptor, so it stopped at NOP. NOP raised the interrupt, but STOP was never reached and the channel stayed active. The Mac OS X driver is more tolerant of this, which is why it was not an issue there. The DBDMA Specification, section 1.4, says: "The target fetches command entries and performs the command-entry-specified data-transfer operation, processing command entries until a STOP entry is reached". Keep interpreting ready commands until a transfer blocks or the channel stops, as start() and resume() already did. This is closer to the hardware behavior, and empirically lets Mac OS 8.1 boot again.

With #214 we started to advertise the IDE DMA support from #192 to guests. That appeared to break booting Mac OS 8.x, at least on the Beige G3: the startup disk was not even detected. Mac OS 8.1 sets up an IDE DMA read as INPUT_MORE, then a NOP with its i field set to always, then STOP, which clears the channel's ACTIVE bit. The emulated transfer completion path interpreted only one following descriptor, so it stopped at NOP. NOP raised the interrupt, but STOP was never reached and the channel stayed active. The Mac OS X driver is more tolerant of this, which is why it was not an issue there. The DBDMA Specification, section 1.4, says: "The target fetches command entries and performs the command-entry-specified data-transfer operation, processing command entries until a STOP entry is reached". Keep interpreting ready commands until a transfer blocks or the channel stops, as start() and resume() already did. This is closer to the hardware behavior, and empirically lets Mac OS 8.1 boot again.

With dingusdev#214 we started to advertise the IDE DMA support from dingusdev#192 to guests. That appeared to break booting Mac OS 8.x, at least on the Beige G3: the startup disk was not even detected. Mac OS 8.1 sets up an IDE DMA read as INPUT_MORE, then a NOP with its i field set to always, then STOP, which clears the channel's ACTIVE bit. The emulated transfer completion path interpreted only one following descriptor, so it stopped at NOP. NOP raised the interrupt, but STOP was never reached and the channel stayed active. The Mac OS X driver is more tolerant of this, which is why it was not an issue there. The DBDMA Specification, section 1.4, says: "The target fetches command entries and performs the command-entry-specified data-transfer operation, processing command entries until a STOP entry is reached". Keep interpreting ready commands until a transfer blocks or the channel stops, as start() and resume() already did. This is closer to the hardware behavior, and empirically lets Mac OS 8.1 boot again.

mihaip · 2026-07-11T22:51:05Z

Add read/write DMA support to ATA devices (mostly reusing existing PIO read and write paths).

We also need to advance data_ptr across DMA pulls so transfers can span multiple DBDMA descriptors.

Fixes#154

dingusdev