Archipelago » qemu

/*

 * QEMU EEPROM 93xx emulation

 *

 * Copyright (c) 2006-2007 Stefan Weil

 *

 * This program is free software; you can redistribute it and/or modify

 * it under the terms of the GNU General Public License as published by

 * the Free Software Foundation; either version 2 of the License, or

 * (at your option) any later version.

 *

 * This program is distributed in the hope that it will be useful,

 * but WITHOUT ANY WARRANTY; without even the implied warranty of

 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the

 * GNU General Public License for more details.

 *

 * You should have received a copy of the GNU General Public License

 * along with this program; if not, write to the Free Software

 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301  USA

 */

/* Emulation for serial EEPROMs:

 * NMC93C06 256-Bit (16 x 16)

 * NMC93C46 1024-Bit (64 x 16)

 * NMC93C56 2028 Bit (128 x 16)

 * NMC93C66 4096 Bit (256 x 16)

 * Compatible devices include FM93C46 and others.

 *

 * Other drivers use these interface functions:

 * eeprom93xx_new   - add a new EEPROM (with 16, 64 or 256 words)

 * eeprom93xx_free  - destroy EEPROM

 * eeprom93xx_read  - read data from the EEPROM

 * eeprom93xx_write - write data to the EEPROM

 * eeprom93xx_data  - get EEPROM data array for external manipulation

 *

 * Todo list:

 * - No emulation of EEPROM timings.

 */

#include <assert.h>

#include "eeprom93xx.h"

/* Debug EEPROM emulation. */

//~ #define DEBUG_EEPROM

#ifdef DEBUG_EEPROM

#define logout(fmt, args...) fprintf(stderr, "EEPROM\t%-24s" fmt, __func__, ##args)

#else

#define logout(fmt, args...) ((void)0)

#endif

static int eeprom_instance = 0;

static const int eeprom_version = 20061112;

#if 0

typedef enum {

  eeprom_read  = 0x80,   /* read register xx */

  eeprom_write = 0x40,   /* write register xx */

  eeprom_erase = 0xc0,   /* erase register xx */

  eeprom_ewen  = 0x30,   /* erase / write enable */

  eeprom_ewds  = 0x00,   /* erase / write disable */

  eeprom_eral  = 0x20,   /* erase all registers */

  eeprom_wral  = 0x10,   /* write all registers */

  eeprom_amask = 0x0f,

  eeprom_imask = 0xf0

} eeprom_instruction_t;

#endif

#ifdef DEBUG_EEPROM

static const char *opstring[] = {

  "extended", "write", "read", "erase"

};

#endif

struct _eeprom_t {

    uint8_t  tick;

    uint8_t  address;

    uint8_t  command;

    uint8_t  writeable;

    uint8_t eecs;

    uint8_t eesk;

    uint8_t eedo;

    uint8_t  addrbits;

    uint8_t  size;

    uint16_t data;

    uint16_t contents[0];

};

/* Code for saving and restoring of EEPROM state. */

static void eeprom_save(QEMUFile *f, void *opaque)

{

    /* Save EEPROM data. */

    unsigned address;

    eeprom_t *eeprom = (eeprom_t *)opaque;

    qemu_put_buffer(f, (uint8_t *)eeprom, sizeof(*eeprom) - 2);

    qemu_put_be16(f, eeprom->data);

    for (address = 0; address < eeprom->size; address++) {

        qemu_put_be16(f, eeprom->contents[address]);

    }

}

static int eeprom_load(QEMUFile *f, void *opaque, int version_id)

{

    /* Load EEPROM data from saved data if version and EEPROM size

       of data and current EEPROM are identical. */

    eeprom_t *eeprom = (eeprom_t *)opaque;

    int result = -EINVAL;

    if (version_id == eeprom_version) {

        unsigned address;

        uint8_t size = eeprom->size;

        qemu_get_buffer(f, (uint8_t *)eeprom, sizeof(*eeprom) - 2);

        if (eeprom->size == size) {

            eeprom->data = qemu_get_be16(f);

            for (address = 0; address < eeprom->size; address++) {

                eeprom->contents[address] = qemu_get_be16(f);

            }

            result = 0;

        }

    }

    return result;

}

void eeprom93xx_write(eeprom_t *eeprom, int eecs, int eesk, int eedi)

{

    uint8_t tick = eeprom->tick;

    uint8_t eedo = eeprom->eedo;

    uint16_t address = eeprom->address;

    uint8_t command = eeprom->command;

    logout("CS=%u SK=%u DI=%u DO=%u, tick = %u\n",

           eecs, eesk, eedi, eedo, tick);

    if (! eeprom->eecs && eecs) {

        /* Start chip select cycle. */

        logout("Cycle start, waiting for 1st start bit (0)\n");

        tick = 0;

        command = 0x0;

        address = 0x0;

    } else if (eeprom->eecs && ! eecs) {

        /* End chip select cycle. This triggers write / erase. */

        if (eeprom->writeable) {

            uint8_t subcommand = address >> (eeprom->addrbits - 2);

            if (command == 0 && subcommand == 2) {

                /* Erase all. */

                for (address = 0; address < eeprom->size; address++) {

                    eeprom->contents[address] = 0xffff;

                }

            } else if (command == 3) {

                /* Erase word. */

                eeprom->contents[address] = 0xffff;

            } else if (tick >= 2 + 2 + eeprom->addrbits + 16) {

                if (command == 1) {

                    /* Write word. */

                    eeprom->contents[address] &= eeprom->data;

                } else if (command == 0 && subcommand == 1) {

                    /* Write all. */

                    for (address = 0; address < eeprom->size; address++) {

                        eeprom->contents[address] &= eeprom->data;

                    }

                }

            }

        }

        /* Output DO is tristate, read results in 1. */

        eedo = 1;

    } else if (eecs && ! eeprom->eesk && eesk) {

        /* Raising edge of clock shifts data in. */

        if (tick == 0) {

            /* Wait for 1st start bit. */

            if (eedi == 0) {

                logout("Got correct 1st start bit, waiting for 2nd start bit (1)\n");

                tick++;

            } else {

                logout("wrong 1st start bit (is 1, should be 0)\n");

                tick = 2;

                //~ assert(!"wrong start bit");

            }

        } else if (tick == 1) {

            /* Wait for 2nd start bit. */

            if (eedi != 0) {

                logout("Got correct 2nd start bit, getting command + address\n");

                tick++;

            } else {

                logout("1st start bit is longer than needed\n");

            }

        } else if (tick < 2 + 2) {

            /* Got 2 start bits, transfer 2 opcode bits. */

            tick++;

            command <<= 1;

            if (eedi) {

                command += 1;

            }

        } else if (tick < 2 + 2 + eeprom->addrbits) {

            /* Got 2 start bits and 2 opcode bits, transfer all address bits. */

            tick++;

            address = ((address << 1) | eedi);

            if (tick == 2 + 2 + eeprom->addrbits) {

                logout("%s command, address = 0x%02x (value 0x%04x)\n",

                       opstring[command], address, eeprom->contents[address]);

                if (command == 2) {

                    eedo = 0;

                }

                address = address % eeprom->size;

                if (command == 0) {

                    /* Command code in upper 2 bits of address. */

                    switch (address >> (eeprom->addrbits - 2)) {

                        case 0:

                            logout("write disable command\n");

                            eeprom->writeable = 0;

                            break;

                        case 1:

                            logout("write all command\n");

                            break;

                        case 2:

                            logout("erase all command\n");

                            break;

                        case 3:

                            logout("write enable command\n");

                            eeprom->writeable = 1;

                            break;

                    }

                } else {

                    /* Read, write or erase word. */

                    eeprom->data = eeprom->contents[address];

                }

            }

        } else if (tick < 2 + 2 + eeprom->addrbits + 16) {

            /* Transfer 16 data bits. */

            tick++;

            if (command == 2) {

                /* Read word. */

                eedo = ((eeprom->data & 0x8000) != 0);

            }

            eeprom->data <<= 1;

            eeprom->data += eedi;

        } else {

            logout("additional unneeded tick, not processed\n");

        }

    }

    /* Save status of EEPROM. */

    eeprom->tick = tick;

    eeprom->eecs = eecs;

    eeprom->eesk = eesk;

    eeprom->eedo = eedo;

    eeprom->address = address;

    eeprom->command = command;

}

uint16_t eeprom93xx_read(eeprom_t *eeprom)

{

    /* Return status of pin DO (0 or 1). */

    logout("CS=%u DO=%u\n", eeprom->eecs, eeprom->eedo);

    return (eeprom->eedo);

}

#if 0

void eeprom93xx_reset(eeprom_t *eeprom)

{

    /* prepare eeprom */

    logout("eeprom = 0x%p\n", eeprom);

    eeprom->tick = 0;

    eeprom->command = 0;

}

#endif

eeprom_t *eeprom93xx_new(uint16_t nwords)

{

    /* Add a new EEPROM (with 16, 64 or 256 words). */

    eeprom_t *eeprom;

    uint8_t addrbits;

    switch (nwords) {

        case 16:

        case 64:

            addrbits = 6;

            break;

        case 128:

        case 256:

            addrbits = 8;

            break;

        default:

            assert(!"Unsupported EEPROM size, fallback to 64 words!");

            nwords = 64;

            addrbits = 6;

    }

    eeprom = (eeprom_t *)qemu_mallocz(sizeof(*eeprom) + nwords * 2);

    eeprom->size = nwords;

    eeprom->addrbits = addrbits;

    /* Output DO is tristate, read results in 1. */

    eeprom->eedo = 1;

    logout("eeprom = 0x%p, nwords = %u\n", eeprom, nwords);

    register_savevm("eeprom", eeprom_instance, eeprom_version,

                    eeprom_save, eeprom_load, eeprom);

    return eeprom;

}

void eeprom93xx_free(eeprom_t *eeprom)

{

    /* Destroy EEPROM. */

    logout("eeprom = 0x%p\n", eeprom);

    qemu_free(eeprom);

}

uint16_t *eeprom93xx_data(eeprom_t *eeprom)

{

    /* Get EEPROM data array. */

    return &eeprom->contents[0];

}

/* eof */