gint/TODO
Lephe c9264a06d5
kernel: driver and world system overhaul
Changes in the driver and world system:

* Rewrite driver logic to include more advanced concepts. The notion of
  binding a driver to a device is introduced to formalize wait(); power
  management is now built-in instead of being handled by the drivers
  (for instance DMA). The new driver model is described in great detail
  in <gint/drivers.h>

* Formalized the concept of "world switch" where the hardware state is
  saved and later restored. As a tool, the world switch turns out to be
  very stable, and allows a lot of hardware manipulation that would be
  edgy at best when running in the OS world.

* Added a GINT_DRV_SHARED flag for drivers to specify that their state
  is shared between worlds and not saved/restored. This has a couple of
  uses.

* Exposed a lot more of the internal driver/world system as their is no
  particular downside to it. This includes stuff in <gint/drivers.h>
  and the driver's state structures in <gint/drivers/states.h>. This is
  useful for debugging and for cracked concepts, but there is no
  API stability guarantee.

* Added a more flexible driver level system that allows any 2-digit
  level to be used.

Feature changes:

* Added a CPU driver that provides the VBR change as its state save.
  Because the whole context switch relied on interrupts being disabled
  anyway, there is no longer an inversion of control when setting the
  VBR; this is just part of the CPU driver's configuration. The CPU
  driver may also support other features such as XYRAM block transfer
  in the future.

* Moved gint_inthandler() to the INTC driver under the name
  intc_handler(), pairing up again with intc_priority().

* Added a reentrant atomic lock based on the test-and-set primitive.
  Interrupts are disabled with IMASK=15 for the duration of atomic
  operations.

* Enabled the DMA driver on SH7305-based fx-9860G. The DMA provides
  little benefit on this platform because the RAM is generally faster
  and buffers are ultimately small. The DMA is still not available on
  SH3-based fx-9860G models.

* Solved an extremely obnoxious bug in timer_spin_wait() where the
  timer is not freed, causing the callback to be called when interrupts
  are re-enabled. This increments a random value on the stack. As a
  consequence of the change, removed the long delays in the USB driver
  since they are not actually needed.

Minor changes:

* Deprecated some of the elements in <gint/hardware.h>. There really is
  no good way to "enumerate" devices yet.

* Deprecated gint_switch() in favor of a new function
  gint_world_switch() which uses the GINT_CALL abstraction.

* Made the fx-9860G VRAM 32-aligned so that it can be used for tests
  with the DMA.

Some features of the driver and world systems have not been implemented
yet, but may be in the future:

* Some driver flags should be per-world in order to create multiple
  gint worlds. This would be useful in Yatis' hypervisor.
* A GINT_DRV_LAZY flag would be useful for drivers that don't want to
  be started up automatically during a world switch. This is relevant
  for drivers that have a slow start/stop sequence. However, this is
  tricky to do correctly as it requires dynamic start/stop and also
  tracking which world the current hardware state belongs to.
2021-04-23 20:44:08 +02:00

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Extensions on existing code:
* bfile: implement the optimization-restart as realized by Kbd2
* kernel: use GINT_CALL() for all callbacks, without breaking the timer API
* kernel: better restore to userspace before panic (ensure BL=0 IMASK=0)
* project: add license file
* kernel: group linker script symbols in a single header file
* bopti: try to display fullscreen images with TLB access + DMA on fxcg50
* core: try to leave add-in without reset in case of panic
* core: use cmp/str for memchr()
* r61524: brightness control and clean the file
* core: review forgotten globals and MPU addresses not in <gint/mpu/*.h>
* core: run destructors when a task-switch results in leaving the app
* core rtc: use qdiv10 to massively improve division performance
Future directions.
* A complete file system abstraction
* Integrate overclock management
* Audio playback using TSWilliamson's libsnd method
* Serial communication
* USB communication, using Yatis' reverse-engineering of the module
* Make fx9860g projects work out of the box on fxcg50
* Use the DSP to enhance parallel computation
* Base for Yatis' threads library