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// # << NEORV32: neorv32_cpu.c - CPU Core Functions HW Driver >>                                   #

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// # BSD 3-Clause License                                                                          #

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// # Copyright (c) 2020, Stephan Nolting. All rights reserved.                                     #

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// # The NEORV32 Processor - https://github.com/stnolting/neorv32              (c) Stephan Nolting #

// #################################################################################################

/**********************************************************************//**

 * @file neorv32_cpu.c

 * @author Stephan Nolting

 * @brief CPU Core Functions HW driver source file.

 **************************************************************************/

#include "neorv32.h"

#include "neorv32_cpu.h"

/**********************************************************************//**

 * Enable specific CPU interrupt.

 *

 * @note Interrupts have to be globally enabled via neorv32_cpu_eint(void), too.

 *

 * @param[in] irq_sel CPU interrupt select. See #NEORV32_CPU_MIE_enum.

 * @return 0 if success, 1 if error (invalid irq_sel).

 **************************************************************************/

int neorv32_cpu_irq_enable(uint8_t irq_sel) {

  if ((irq_sel != CPU_MIE_MSIE) && (irq_sel != CPU_MIE_MTIE) && (irq_sel != CPU_MIE_MEIE) &&

      (irq_sel != CPU_MIE_FIRQ0E) && (irq_sel != CPU_MIE_FIRQ1E) && (irq_sel != CPU_MIE_FIRQ2E) && (irq_sel != CPU_MIE_FIRQ3E)) {

    return 1;

  }

  register uint32_t mask = (uint32_t)(1 << irq_sel);

  asm volatile ("csrrs zero, mie, %0" : : "r" (mask));

  return 0;

}

/**********************************************************************//**

 * Disable specific CPU interrupt.

 *

 * @param[in] irq_sel CPU interrupt select. See #NEORV32_CPU_MIE_enum.

 * @return 0 if success, 1 if error (invalid irq_sel).

 **************************************************************************/

int neorv32_cpu_irq_disable(uint8_t irq_sel) {

  if ((irq_sel != CPU_MIE_MSIE) && (irq_sel != CPU_MIE_MTIE) && (irq_sel != CPU_MIE_MEIE) &&

      (irq_sel != CPU_MIE_FIRQ0E) && (irq_sel != CPU_MIE_FIRQ1E) && (irq_sel != CPU_MIE_FIRQ2E) && (irq_sel != CPU_MIE_FIRQ3E)) {

    return 1;

  }

  register uint32_t mask = (uint32_t)(1 << irq_sel);

  asm volatile ("csrrc zero, mie, %0" : : "r" (mask));

  return 0;

}

/**********************************************************************//**

 * Get cycle count from cycle[h].

 *

 * @note The cycle[h] CSR is shadowed copy of the mcycle[h] CSR.

 *

 * @return Current cycle counter (64 bit).

 **************************************************************************/

uint64_t neorv32_cpu_get_cycle(void) {

  union {

    uint64_t uint64;

    uint32_t uint32[sizeof(uint64_t)/2];

  } cycles;

  uint32_t tmp1, tmp2, tmp3;

  while(1) {

    tmp1 = neorv32_cpu_csr_read(CSR_CYCLEH);

    tmp2 = neorv32_cpu_csr_read(CSR_CYCLE);

    tmp3 = neorv32_cpu_csr_read(CSR_CYCLEH);

    if (tmp1 == tmp3) {

      break;

    }

  }

  cycles.uint32[0] = tmp2;

  cycles.uint32[1] = tmp3;

  return cycles.uint64;

}

/**********************************************************************//**

 * Set mcycle[h] counter.

 *

 * @param[in] value New value for mcycle[h] CSR (64-bit).

 **************************************************************************/

void neorv32_cpu_set_mcycle(uint64_t value) {

  union {

    uint64_t uint64;

    uint32_t uint32[sizeof(uint64_t)/2];

  } cycles;

  cycles.uint64 = value;

  neorv32_cpu_csr_write(CSR_MCYCLE,  0);

  neorv32_cpu_csr_write(CSR_MCYCLEH, cycles.uint32[1]);

  neorv32_cpu_csr_write(CSR_MCYCLE,  cycles.uint32[0]);

}

/**********************************************************************//**

 * Get retired instructions counter from instret[h].

 *

 * @note The instret[h] CSR is shadowed copy of the instret[h] CSR.

 *

 * @return Current instructions counter (64 bit).

 **************************************************************************/

uint64_t neorv32_cpu_get_instret(void) {

  union {

    uint64_t uint64;

    uint32_t uint32[sizeof(uint64_t)/2];

  } cycles;

  uint32_t tmp1, tmp2, tmp3;

  while(1) {

    tmp1 = neorv32_cpu_csr_read(CSR_INSTRETH);

    tmp2 = neorv32_cpu_csr_read(CSR_INSTRET);

    tmp3 = neorv32_cpu_csr_read(CSR_INSTRETH);

    if (tmp1 == tmp3) {

      break;

    }

  }

  cycles.uint32[0] = tmp2;

  cycles.uint32[1] = tmp3;

  return cycles.uint64;

}

/**********************************************************************//**

 * Set retired instructions counter minstret[h].

 *

 * @param[in] value New value for mcycle[h] CSR (64-bit).

 **************************************************************************/

void neorv32_cpu_set_minstret(uint64_t value) {

  union {

    uint64_t uint64;

    uint32_t uint32[sizeof(uint64_t)/2];

  } cycles;

  cycles.uint64 = value;

  neorv32_cpu_csr_write(CSR_MINSTRET,  0);

  neorv32_cpu_csr_write(CSR_MINSTRETH, cycles.uint32[1]);

  neorv32_cpu_csr_write(CSR_MINSTRET,  cycles.uint32[0]);

}

/**********************************************************************//**

 * Get current system time from time[h] CSR.

 *

 * @note This function requires the MTIME system timer to be implemented.

 *

 * @return Current system time (64 bit).

 **************************************************************************/

uint64_t neorv32_cpu_get_systime(void) {

  union {

    uint64_t uint64;

    uint32_t uint32[sizeof(uint64_t)/2];

  } cycles;

  uint32_t tmp1, tmp2, tmp3;

  while(1) {

    tmp1 = neorv32_cpu_csr_read(CSR_TIMEH);

    tmp2 = neorv32_cpu_csr_read(CSR_TIME);

    tmp3 = neorv32_cpu_csr_read(CSR_TIMEH);

    if (tmp1 == tmp3) {

      break;

    }

  }

  cycles.uint32[0] = tmp2;

  cycles.uint32[1] = tmp3;

  return cycles.uint64;

}

/**********************************************************************//**

 * Simple delay function using busy wait.

 *

 * @warning This function requires the cycle CSR(s). Hence, the Zicsr extension is mandatory.

 *

 * @param[in] time_ms Time in ms to wait.

 **************************************************************************/

void neorv32_cpu_delay_ms(uint32_t time_ms) {

  uint64_t time_resume = neorv32_cpu_get_cycle();

  uint32_t clock = SYSINFO_CLK; // clock ticks per second

  clock = clock / 1000; // clock ticks per ms

  uint64_t wait_cycles = ((uint64_t)clock) * ((uint64_t)time_ms);

  time_resume += wait_cycles;

  while(1) {

    if (neorv32_cpu_get_cycle() >= time_resume) {

      break;

    }

  }

}

/**********************************************************************//**

 * Switch from privilege mode MACHINE to privilege mode USER.

 *

 * @warning This function requires the U extension to be implemented.

 **************************************************************************/

void __attribute__((naked)) neorv32_cpu_goto_user_mode(void) {

  // make sure to use NO registers in here! -> naked

  asm volatile ("csrw mepc, ra           \n\t" // move return address to mepc so we can return using "mret". also, we can now use ra as general purpose register in here

                "li ra, %[input_imm]     \n\t" // bit mask to clear the two MPP bits

                "csrrc zero, mstatus, ra \n\t" // clear MPP bits -> MPP=u-mode

                "mret                    \n\t" // return and switch to user mode

                :  : [input_imm] "i" ((1<<CPU_MSTATUS_MPP_H) | (1<<CPU_MSTATUS_MPP_L)));

}

/**********************************************************************//**

 * Atomic compare-and-swap operation (for implemeneting semaphores and mutexes).

 *

 * @warning This function requires the A (atomic) CPU extension.

 *

 * @param[in] addr Address of memory location.

 * @param[in] expected Expected value (for comparison).

 * @param[in] desired Desired value (new value).

 * @return Returns 0 on success, 1 on failure.

 **************************************************************************/

int __attribute__ ((noinline)) neorv32_cpu_atomic_cas(uint32_t addr, uint32_t expected, uint32_t desired) {

#ifdef __riscv_atomic

  register uint32_t addr_reg = addr;

  register uint32_t des_reg = desired;

  register uint32_t tmp_reg;

  // load original value + reservation (lock)

  asm volatile ("lr.w %[result], (%[input])" : [result] "=r" (tmp_reg) : [input] "r" (addr_reg));

  if (tmp_reg != expected) {

    asm volatile ("lw x0, 0(%[input])" : : [input] "r" (addr_reg)); // clear reservation lock

    return 1;

  }

  // store-conditional

  asm volatile ("sc.w %[result], %[input_i], (%[input_j])" : [result] "=r" (tmp_reg) : [input_i] "r" (des_reg), [input_j] "r" (addr_reg));

  if (tmp_reg) {

    return 1;

  }

  return 0;

#else

  return 1; // A extension not implemented -Y always fail

#endif

}

/**********************************************************************//**

 * Physical memory protection (PMP): Get minimal region size (granularity).

 *

 * @warning This function overrides PMPCFG0[0] and PMPADDR0 CSRs.

 *

 * @warning This function requires the PMP CPU extension.

 *

 * @return Returns minimal region size in bytes; Returns 0 on failure.

 **************************************************************************/

uint32_t neorv32_cpu_pmp_get_granularity(void) {

  if ((neorv32_cpu_csr_read(CSR_MZEXT) & (1<<CPU_MZEXT_PMP)) == 0) {

    return 0; // PMP not implemented

  }

  // check min granulartiy

  uint32_t tmp = neorv32_cpu_csr_read(CSR_PMPCFG0);

  tmp &= 0xffffff00; // disable entry 0

  neorv32_cpu_csr_write(CSR_PMPCFG0, tmp);

  neorv32_cpu_csr_write(CSR_PMPADDR0, 0xffffffff);

  uint32_t tmp_a = neorv32_cpu_csr_read(CSR_PMPADDR0);

  uint32_t i;

  // find least-significat set bit

  for (i=31; i!=0; i--) {

    if (((tmp_a >> i) & 1) == 0) {

      break;

    }

  }

  return (uint32_t)(1 << (i+1+2));

}

/**********************************************************************//**

 * Physical memory protection (PMP): Configure region.

 *

 * @note Using NAPOT mode - page base address has to be naturally aligned.

 *

 * @warning This function requires the PMP CPU extension.

 *

 * @param[in] index Region number (index, 0..max_regions-1).

 * @param[in] base Region base address (has to be naturally aligned!).

 * @param[in] size Region size, has to be a power of 2 (min 8 bytes or according to HW's PMP.granularity configuration).

 * @param[in] config Region configuration (attributes) byte (for PMPCFGx).

 * @return Returns 0 on success, 1 on failure.

 **************************************************************************/

int neorv32_cpu_pmp_configure_region(uint32_t index, uint32_t base, uint32_t size, uint8_t config) {

  if ((neorv32_cpu_csr_read(CSR_MZEXT) & (1<<CPU_MZEXT_PMP)) == 0) {

    return 1; // PMP not implemented

  }

  if (size < 8) {

    return 1; // minimal region size is 8 bytes

  }

  if ((size & (size - 1)) != 0) {

    return 1; // region size is not a power of two

  }

  // setup configuration

  uint32_t tmp;

  uint32_t config_int  = ((uint32_t)config) << ((index%4)*8);

  uint32_t config_mask = ((uint32_t)0xFF)   << ((index%4)*8);

  config_mask = ~config_mask;

  // clear old configuration

  if (index < 3) {

    tmp = neorv32_cpu_csr_read(CSR_PMPCFG0);

    tmp &= config_mask; // clear old config

    neorv32_cpu_csr_write(CSR_PMPCFG0, tmp);

  }

  else {

    tmp = neorv32_cpu_csr_read(CSR_PMPCFG1);

    tmp &= config_mask; // clear old config

    neorv32_cpu_csr_write(CSR_PMPCFG1, tmp);

  }

  // set base address and region size

  uint32_t addr_mask = ~((size - 1) >> 2);

  uint32_t size_mask = (size - 1) >> 3;

  tmp = base & addr_mask;

  tmp = tmp | size_mask;

  switch(index & 7) {

    case 0: neorv32_cpu_csr_write(CSR_PMPADDR0, tmp); break;

    case 1: neorv32_cpu_csr_write(CSR_PMPADDR1, tmp); break;

    case 2: neorv32_cpu_csr_write(CSR_PMPADDR2, tmp); break;

    case 3: neorv32_cpu_csr_write(CSR_PMPADDR3, tmp); break;

    case 4: neorv32_cpu_csr_write(CSR_PMPADDR4, tmp); break;

    case 5: neorv32_cpu_csr_write(CSR_PMPADDR5, tmp); break;

    case 6: neorv32_cpu_csr_write(CSR_PMPADDR6, tmp); break;

    case 7: neorv32_cpu_csr_write(CSR_PMPADDR7, tmp); break;

    default: break;

  }

  // wait for HW to computer PMP-internal stuff (address masks)

  for (tmp=0; tmp<16; tmp++) {

    asm volatile ("nop");

  }

  // set new configuration

  if (index < 3) {

    tmp = neorv32_cpu_csr_read(CSR_PMPCFG0);

    tmp |= config_int; // set new config

    neorv32_cpu_csr_write(CSR_PMPCFG0, tmp);

  }

  else {

    tmp = neorv32_cpu_csr_read(CSR_PMPCFG1);

    tmp |= config_int; // set new config

    neorv32_cpu_csr_write(CSR_PMPCFG1, tmp);

  }

  return 0;

}