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// # << NEORV32 - Physical Memory Protection Example Program >>                                    #

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// # Copyright (c) 2022, Stephan Nolting. All rights reserved.                                     #

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

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

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

 * @file demo_pmp/main.c

 * @author Stephan Nolting

 * @brief Physical memory protection (PMP) example program.

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

#include <neorv32.h>

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

 * @name User configuration

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

/**@{*/

/** UART BAUD rate */

#define BAUD_RATE 19200

/**@}*/

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

 * Example variable that will be protected by the PMP

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

uint32_t protected_var[4] = {

  0x11223344,

  0x55667788,

  0x00CAFE00,

  0xDEADC0DE

};

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

 * Main function

 *

 * @note This program requires the CPU PMP extension (with at least 2 regions) and UART0.

 *

 * @return 0 if execution was successful

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

int main() {

  // initialize NEORV32 run-time environment

  neorv32_rte_setup();

  // setup UART0 at default baud rate, no parity bits, no HW flow control

  neorv32_uart0_setup(BAUD_RATE, PARITY_NONE, FLOW_CONTROL_NONE);

  // check if UART0 is implemented

  if (neorv32_uart0_available() == 0) {

    return 1; // UART0 not available, exit

  }

  // check if PMP is implemented at all

  if ((neorv32_cpu_csr_read(CSR_MXISA) & (1 << CSR_MXISA_PMP)) == 0) {

    neorv32_uart0_printf("ERROR! PMP CPU extension not implemented!\n");

    return 1;

  }

  // intro

  neorv32_uart0_printf("\n<<< NEORV32 Physical Memory Protection (PMP) Example Program >>>\n\n");

  neorv32_uart0_printf("NOTE: This program requires at least 2 PMP regions (PMP_NUM_REGIONS >= 2)\n"

                       "      and a minimal granularity of 4 bytes (PMP_MIN_GRANULARITY = 4).\n\n");

  neorv32_uart0_printf("NOTE: A 4-word array 'protected_var[4]' is created, which will be probed from\n"

                       "      **machine-mode**. It provides the following access rights:\n"

                       "      - NO_EXECUTE\n"

                       "      - NO_WRITE\n"

                       "      - READ\n"

                       "      - LOCKED - also enforce access rights for machine-mode software\n\n");

  // show PMP configuration

  neorv32_uart0_printf("PMP hardware configuration:\n");

  neorv32_uart0_printf("> Number of regions: %u\n", neorv32_cpu_pmp_get_num_regions());

  neorv32_uart0_printf("> Min. granularity:  %u bytes (minimal region size)\n\n", neorv32_cpu_pmp_get_granularity());

  // The "protected_var" variable will be protected: No execute and no write access, just allow read access

  // create protected region

  int pmp_status;

  uint8_t permissions;

  neorv32_uart0_printf("Creating protected regions (any access within [REGION_BEGIN <= address < REGION_END] will match the PMP rules)...\n");

  // any access in "region_begin <= address < region_end" will match the PMP rule

  uint32_t region_begin = (uint32_t)(&protected_var[0]);

  uint32_t region_end   = (uint32_t)(&protected_var[4]) + 4;

  neorv32_uart0_printf("REGION_BEGIN = 0x%x\n", region_begin);

  neorv32_uart0_printf("REGION_END   = 0x%x\n", region_end);

  // base (region begin)

  permissions = PMP_OFF << PMPCFG_A_LSB; // mode = OFF

  neorv32_uart0_printf("> Region begin (PMP entry 0): Base = 0x%x, Mode = OFF (base of region) ", region_begin);

  pmp_status = neorv32_cpu_pmp_configure_region(0, region_begin, permissions);

  if (pmp_status) {

    neorv32_uart0_printf("[FAILED]\n");

  }

  else {

    neorv32_uart0_printf("[ok]\n");

  }

  // bound (region end)

  permissions = (PMP_TOR << PMPCFG_A_LSB) | // enable entry as TOR = top of region

                (0 << PMPCFG_X) | // no "execute" permission

                (0 << PMPCFG_W) | // no "write" permission

                (1 << PMPCFG_R) | // set "read" permission

                (1 << PMPCFG_L);  // locked: also enforce PMP rule for machine-mode software

  neorv32_uart0_printf("> Region end   (PMP entry 1): Base = 0x%x, Mode = TOR (top of region)  ", region_end);

  pmp_status = neorv32_cpu_pmp_configure_region(1, region_end, permissions);

  if (pmp_status) {

    neorv32_uart0_printf("[FAILED]\n");

  }

  else {

    neorv32_uart0_printf("[ok]\n");

  }

  // test access

  neorv32_uart0_printf("\nTesting access to 'protected_var' - invalid accesses will raise an exception, which will be\n"

                       "captured by the NEORV32 runtime environment's dummy/debug handlers ('<RTE> ... </RTE>').\n\n");

  neorv32_uart0_printf("Reading protected_var[0] = 0x%x\n", protected_var[0]);

  neorv32_uart0_printf("Reading protected_var[1] = 0x%x\n", protected_var[1]);

  neorv32_uart0_printf("Reading protected_var[2] = 0x%x\n", protected_var[2]);

  neorv32_uart0_printf("Reading protected_var[3] = 0x%x\n\n", protected_var[3]);

  neorv32_uart0_printf("Trying to write protected_var[0]... ");

  protected_var[0] = 0; // should fail!

  neorv32_uart0_printf("Trying to write protected_var[1]... ");

  protected_var[1] = 0; // should fail!

  neorv32_uart0_printf("Trying to write protected_var[2]... ");

  protected_var[2] = 0; // should fail!

  neorv32_uart0_printf("Trying to write protected_var[3]... ");

  protected_var[3] = 0; // should fail!

  neorv32_uart0_printf("\nReading again protected_var[0] = 0x%x\n", protected_var[0]);

  neorv32_uart0_printf("Reading again protected_var[1] = 0x%x\n", protected_var[1]);

  neorv32_uart0_printf("Reading again protected_var[2] = 0x%x\n", protected_var[2]);

  neorv32_uart0_printf("Reading again protected_var[3] = 0x%x\n\n", protected_var[3]);

  neorv32_uart0_printf("\nPMP demo program completed.\n");

  return 0;

}