plic.c

/*
 * Copyright (c) 2006-2021, RT-Thread Development Team
 *
 * SPDX-License-Identifier: Apache-2.0
 *
 * Change Logs:
 * Date           Author       Notes
 * 2021-05-20     bigmagic     first version
 */
#include "rtthread.h"
#include "plic.h"
#include <riscv_io.h>
#include "encoding.h"

/*
* Each PLIC interrupt source can be assigned a priority by writing
* to its 32-bit memory-mapped priority register.
* The QEMU-virt (the same as FU540-C000) supports 7 levels of priority.
* A priority value of 0 is reserved to mean "never interrupt" and
* effectively disables the interrupt.
* Priority 1 is the lowest active priority, and priority 7 is the highest.
* Ties between global interrupts of the same priority are broken by
* the Interrupt ID; interrupts with the lowest ID have the highest
* effective priority.
*/
void plic_set_priority(int irq, int priority)
{
    *(uint32_t*)PLIC_PRIORITY(irq) = priority;
}

/*
* Each global interrupt can be enabled by setting the corresponding
* bit in the enables registers.
*/
void plic_irq_enable(int irq)
{
    int hart = r_mhartid();
    *(uint32_t*)PLIC_ENABLE(hart) = ((*(uint32_t*)PLIC_ENABLE(hart)) | (1 << irq));
#ifdef  RISCV_S_MODE
    set_csr(sie, read_csr(sie) | MIP_SEIP);
#else
    set_csr(mie, read_csr(mie) | MIP_MEIP);
#endif
}

void plic_irq_disable(int irq)
{
    int hart = r_mhartid();
    *(uint32_t*)PLIC_ENABLE(hart) = (((*(uint32_t*)PLIC_ENABLE(hart)) & (~(1 << irq))));
}

/*
* PLIC will mask all interrupts of a priority less than or equal to threshold.
* Maximum threshold is 7.
* For example, a threshold value of zero permits all interrupts with
* non-zero priority, whereas a value of 7 masks all interrupts.
* Notice, the threshold is global for PLIC, not for each interrupt source.
*/
void plic_set_threshold(int threshold)
{
    int hart = r_mhartid();
    *(uint32_t*)PLIC_THRESHOLD(hart) = threshold;
}

/*
 * DESCRIPTION:
 *    Query the PLIC what interrupt we should serve.
 *    Perform an interrupt claim by reading the claim register, which
 *    returns the ID of the highest-priority pending interrupt or zero if there
 *    is no pending interrupt.
 *    A successful claim also atomically clears the corresponding pending bit
 *    on the interrupt source.
 * RETURN VALUE:
 *    the ID of the highest-priority pending interrupt or zero if there
 *    is no pending interrupt.
 */
int plic_claim(void)
{
    int hart = r_mhartid();
    int irq = *(uint32_t*)PLIC_CLAIM(hart);
    return irq;
}

/*
 * DESCRIPTION:
  *    Writing the interrupt ID it received from the claim (irq) to the
 *    complete register would signal the PLIC we've served this IRQ.
 *    The PLIC does not check whether the completion ID is the same as the
 *    last claim ID for that target. If the completion ID does not match an
 *    interrupt source that is currently enabled for the target, the completion
 *    is silently ignored.
 * RETURN VALUE: none
 */
void plic_complete(int irq)
{
    int hart = r_mhartid();
    *(uint32_t*)PLIC_COMPLETE(hart) = irq;
}