PLIC handlers array

[JuanSapriza]

Introduction

To allow for easier extension of X-HEEP (without the need of modifying the PLIC HAL), we have decided to migrate the pre-defined handlers into an array of handlers that can then be filled externally.

During the initialization of the PLIC (through the plic_Init() function the array is filled with

• The fixed handlers of the peripherals that are connected to x-HEEP (e.g. UART, SPI)
• a Dummy handler in any other case.

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Changes

This change required several minor changes:

• The plic_get_irq_src_type function was adapted to fill the handlers array. Now its called plic_reset_handlers_list.
• The i2s HAL was updated to include a weak implementation of the handler, which only existed in the example before.
• The same logic that was implemented in the PLIC was also implemented for the GPIO so:
  • When there is a GPIO interrupt, no matter the ID, the PLIC will call the GPIO handler, passing the ID.
  • The GPIO handler will call a handler stored in the position of the ID relative to the first GPIO ID
  • These functions can be assigned from the application

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Tests

• The example_dma and example_i2s where tested on FPGA and worked. These are the only two HALs that include a handler right now.
• The example_gpio_intr was tested on FPGA flash_load and flash_exec and worked. It implements two interrupts, with two different handlers.
• All apps were simulated in verilator and worked as expected.

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⚠️ Important

• The GPIO handler list depends on the fact that all GPIOs have consecutive IDs
• The I2c implementation of the interrupt in i2c HAL refactor #265 need to be fixed (the substantiation of the first index moved to the I2C side)
• The future sys_init() function that will be developed by @JoseCalero will need to include gpio_reset_all, as there is no gpio_init. If that function is not called, then gpio_reset_handlers_list needs to be called.

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Future work

Some further changes might be needed

• Many of the previous irq handlers where never overridden by the peripherals. They should be created.
• Right now its only possible to assign new handlers to the external interrupts, but maybe its a good idea to expand this possibility to, for instance, the gpios.
• Documentation
• Discussion with @StefanoAlbini96

[JuanSapriza]

The last changes were performed and the documentation in the first comment was updated.
@StefanoAlbini96 @JoseCalero

[JoseCalero]

i modified some minor things, but i still need to modify some other small things in here and I will merge it tomorrow