ardupilot/libraries/AP_Common/AP_Var.cpp

// -*- tab-width: 4; Mode: C++; c-basic-offset: 4; indent-tabs-mode: nil -*-
//
// This is free software; you can redistribute it and/or modify it under
// the terms of the GNU Lesser General Public License as published by the
// Free Software Foundation; either version 2.1 of the License, or (at
// your option) any later version.
//
/// The AP variable interface. This allows different types
/// of variables to be passed to blocks for floating point
/// math, memory management, etc.

#include "AP_Var.h"

// Global constants exported for general use.
//
AP_Float AP_Float_unity         ( 1.0, AP_Var::k_key_none, NULL, AP_Var::k_flag_unlisted);
AP_Float AP_Float_negative_unity(-1.0, AP_Var::k_key_none, NULL, AP_Var::k_flag_unlisted);
AP_Float AP_Float_zero          ( 0.0, AP_Var::k_key_none, NULL, AP_Var::k_flag_unlisted);


// Static member variables for AP_Var.
//
AP_Var      *AP_Var::_variables;
AP_Var      *AP_Var::_grouped_variables;
uint16_t    AP_Var::_tail_sentinel;
bool        AP_Var::_EEPROM_scanned;


// Constructor for standalone variables
//
AP_Var::AP_Var(Key key, const prog_char *name, Flags flags) :
        _group(NULL),
        _key(key | k_key_not_located),
        _name(name),
        _flags(flags)
{
    // Insert the variable or group into the list of known variables, unless
    // it wants to be unlisted.
    //
    if (!has_flags(k_flag_unlisted)) {
        _link = _variables;
        _variables = this;
    }
}

// Constructor for variables in a group
//
AP_Var::AP_Var(AP_Var_group *group, Key index, const prog_char *name, Flags flags) :
        _group(group),
        _key(index),
        _name(name),
        _flags(flags)
{
    AP_Var  **vp;

    // Sort the variable into the list of group-member variables.
    //
    // This list is kept sorted so that groups can traverse forwards along
    // it in order to enumerate their members in key order.
    //
    // We use a pointer-to-pointer insertion technique here; vp points
    // to the pointer to the node that we are considering inserting in front of.
    //
    vp = &_grouped_variables;
    while (*vp != NULL) {
        if ((*vp)->_key > _key) {
               break;
        }
        vp = &((*vp)->_link);
    }
    _link = *vp;
    *vp = this;
}

// Destructor
//
AP_Var::~AP_Var(void)
{
    AP_Var  **vp;

    // Determine which list the variable may be in.
    // If the variable is a group member and the group has already
    // been destroyed, it may not be in any list.
    //
    if (_group) {
        vp = &_grouped_variables;
    } else {
        vp = &_variables;
    }

    // Scan the list and remove this if we find it
    while (*vp) {
        if (*vp == this) {
            *vp = _link;
            break;
        }
        vp = &((*vp)->_link);
    }

    // If we are destroying a group, remove all its variables from the list
    //
    if (has_flags(k_flag_is_group)) {

        // Scan the list and remove any variable that has this as its group
        vp = &_grouped_variables;
        while (*vp) {

            // Does the variable claim us as its group?
            if ((*vp)->_group == this) {
                *vp = (*vp)->_link;
                continue;
            }
            vp = &((*vp)->_link);
        }
    }
}

// Copy the variable's whole name to the supplied buffer.
//
// If the variable is a group member, prepend the group name.
//
void AP_Var::copy_name(char *buffer, size_t buffer_size) const
{
    buffer[0] = '\0';
    if (_group)
        _group->copy_name(buffer, buffer_size);
    strlcat_P(buffer, _name, buffer_size);
}

// Save the variable to EEPROM, if supported
//
bool AP_Var::save(void)
{
    uint8_t vbuf[k_size_max];
    size_t size;

    // if the variable is a group member, save the group
    if (_group) {
        return _group->save();
    }

    // locate the variable in EEPROM, allocating space as required
    if (!_EEPROM_locate(true)) {
        return false;
    }

    // serialize the variable into the buffer and work out how big it is
    size = serialize(vbuf, sizeof(vbuf));

    // if it fit in the buffer, save it to EEPROM
    if (size <= sizeof(vbuf)) {
        eeprom_write_block(vbuf, (void *)_key, size);
    }
    return true;
}

// Load the variable from EEPROM, if supported
//
bool AP_Var::load(void)
{
    uint8_t vbuf[k_size_max];
    size_t size;

    // if the variable is a group member, load the group
    if (_group) {
        return _group->load();
    }

    // locate the variable in EEPROM, but do not allocate space
    if (!_EEPROM_locate(false)) {
        return false;
    }

    // ask the unserializer how big the variable is
    //
    // XXX should check size in EEPROM var header too...
    //
    size = unserialize(NULL, 0);

    // Read the buffer from EEPROM, now that _EEPROM_locate
    // has converted _key into an EEPROM address.
    //
    if (size <= sizeof(vbuf)) {
        eeprom_read_block(vbuf, (void *)_key, size);
        unserialize(vbuf, size);
    }
    return true;
}

// Save all variables that don't opt out.
//
//
bool AP_Var::save_all(void)
{
    bool result = true;
    AP_Var *p = _variables;

    while (p) {
        if (!p->has_flags(k_flag_no_auto_load) &&    // not opted out
            !(p->_group)) {                     // not saved with a group

            if (!p->save()) {
                result = false;
            }
        }
        p = p->_link;
    }
    return result;
}

// Load all variables that don't opt out.
//
bool AP_Var::load_all(void)
{
    bool result;
    AP_Var *p = _variables;

    while (p) {
        if (!p->has_flags(k_flag_no_auto_load) &&    // not opted out
            !(p->_group)) {                     // not loaded with a group

            if (!p->load()) {
                result = false;
            }
        }
        p = p->_link;
    }
    return result;
}

// Erase all variables in EEPROM.
//
void
AP_Var::erase_all()
{
    uint8_t c;

    // overwrite the first byte of the header, invalidating the EEPROM
    //
    c = 0xff;
    eeprom_write_byte(&c, 0);
}

// Return the key for a variable.
//
AP_Var::Key
AP_Var::key(void)
{
    Var_header  var_header;

    if (_group) {                   // group members don't have keys
        return k_key_none;
    }
    if (_key && k_key_not_located) {    // if not located, key is in memory
        return _key & k_key_mask;
    }

    // read key from EEPROM
    eeprom_read_block(&var_header, (void *)_key, sizeof(var_header));
    return var_header.key;
}

// Return the next variable in the global list.
//
AP_Var *
AP_Var::next(void)
{
    // If there is a variable after this one, return it.
    //
    if (_link)
        return _link;

    // If we are at the end of the _variables list, _group will be NULL; in that
    // case, move to the _grouped_variables list.
    //
    if (!_group) {
        return _grouped_variables;
    }

    // We must be at the end of the _grouped_variables list, nothing remains.
    //
    return NULL;
}


// Return the first variable that is a member of the group.
//
AP_Var *
AP_Var::first_member(AP_Var_group *group)
{
    AP_Var  **vp;

    vp = &_grouped_variables;

    while (*vp) {
        if ((*vp)->_group == group) {
            return *vp;
        }
        vp = &((*vp)->_link);
    }
    return NULL;
}

// Return the next variable that is a member of the same group.
AP_Var *
AP_Var::next_member()
{
    AP_Var  *vp;

    vp = _link;
    while (vp) {
        if (vp->_group == _group) {
            return vp;
        }
        vp = vp->_link;
    }
    return NULL;
}

// Scan the EEPROM and assign addresses to all the variables that
// are known and found therein.
//
bool AP_Var::_EEPROM_scan(void)
{
    struct EEPROM_header    ee_header;
    struct Var_header       var_header;
    AP_Var                  *vp;

    // assume that the EEPROM is empty
    _tail_sentinel = 0;

    // read the header and validate
    eeprom_read_block(0, &ee_header, sizeof(ee_header));
    if ((ee_header.magic != k_EEPROM_magic) ||
        (ee_header.revision != k_EEPROM_revision))
        return false;

    // scan the EEPROM
    //
    // Avoid trying to read a header when there isn't enough space left.
    //
    _tail_sentinel = sizeof(ee_header);
    while (_tail_sentinel < (k_EEPROM_size - sizeof(var_header) - 1)) {

        // read a variable header
        eeprom_read_block(&var_header, (void *)_tail_sentinel, sizeof(var_header));

        // if the header is for the sentinel, scanning is complete
        if (var_header.key == k_key_sentinel)
            break;

        // if the variable plus the sentinel would extend past the end of EEPROM, we are done
        if (k_EEPROM_size <= (
                _tail_sentinel +        // current position
                sizeof(ee_header) +     // header for this variable
                var_header.size + 1 +   // data for this variable
                sizeof(ee_header))) {   // header for sentinel
            break;
        }

        // look for a variable with this key
        vp = _variables;
        while (vp) {
            if (vp->key() == var_header.key) {
                // adjust the variable's key to point to this entry
                vp->_key = _tail_sentinel;
                break;
            }
            vp = vp->_link;
        }

        // move to the next variable header
        _tail_sentinel += sizeof(var_header) + var_header.size + 1;
    }

    // Scanning is complete
    _EEPROM_scanned = true;
    return true;
}

// Locate a variable in EEPROM, allocating space if required.
//
bool AP_Var::_EEPROM_locate(bool allocate)
{
    Var_header  var_header;
    Key         new_location;
    size_t      size;

    // Is it a group member, or does it have a no-location key?
    //
    if (_group || (_key == k_key_none)) {
        return false;               // it is/does, and thus it has no location
    }

    // Has the variable already been located?
    //
    if (!(_key & k_key_not_located)) {
        return true;                // it has
    }

    // If the EEPROM has not been scanned, try that now.
    //
    if (!_EEPROM_scanned) {
        _EEPROM_scan();
    }

    // If not located and not permitted to allocate, we have failed.
    //
    if ((_key & k_key_not_located) && !allocate) {
        return false;
    }

    // Ask the serializer for the size of the thing we are allocating, and fail
    // if it is too large or if it has no size, as we will not be able to allocate
    // space for it.
    //
    size = serialize(NULL, 0);
    if ((size == 0) || (size > k_size_max))
        return false;

    // Make sure there will be space in the EEPROM for the variable, its
    // header and the new tail sentinel.
    //
    if ((_tail_sentinel + size + sizeof(Var_header) * 2) > k_EEPROM_size)
        return false;

    // If there is no data in the EEPROM, write the header and move the
    // sentinel.
    //
    if (0 == _tail_sentinel) {
        EEPROM_header   ee_header;

        ee_header.magic = k_EEPROM_magic;
        ee_header.revision = k_EEPROM_revision;
        ee_header.spare = 0;

        eeprom_write_block(0, &ee_header, sizeof(ee_header));

        _tail_sentinel = sizeof(ee_header);
    }

    // Save the location we are going to insert at, and compute the new
    // tail sentinel location.
    //
    _tail_sentinel += sizeof(Var_header) + size;
    new_location = _tail_sentinel;

    // Write the new sentinel first.  If we are interrupted during this operation
    // the old sentinel will still correctly terminate the EEPROM image.
    //
    var_header.key = k_key_sentinel;
    var_header.size = 0;
    eeprom_write_block(&var_header, (void *)_tail_sentinel, sizeof(var_header));

    // Write the header for the block we have just located, claiming the EEPROM space.
    //
    var_header.key = key();
    var_header.size = size - 1;
    eeprom_write_block(&var_header, (void *)new_location, sizeof(Var_header));

    // We have successfully allocated space and thus located the variable.
    //
    _key = new_location;
    return true;
}

size_t
AP_Var_group::serialize(void *buf, size_t buf_size)
{
    return _serialize_unserialize(buf, buf_size, true);
}

size_t
AP_Var_group::unserialize(void *buf, size_t buf_size)
{
    return _serialize_unserialize(buf, buf_size, false);
}

size_t
AP_Var_group::_serialize_unserialize(void *buf, size_t buf_size, bool do_serialize)
{
    AP_Var  *vp;
    uint8_t *bp;
    size_t  size, total_size, resid;

    // Traverse the list of group members, serializing each in order
    //
    vp = first_member(this);
    bp = (uint8_t *)buf;
    resid = buf_size;
    total_size = 0;
    while (vp) {

        // (un)serialise the group member
        if (do_serialize) {
            size = vp->serialize(bp, buf_size);
        } else {
            size = vp->unserialize(bp, buf_size);
        }

        // Account for the space that this variable consumes in the buffer
        //
        // We always count the total size, and we always advance the buffer pointer
        // if there was room for the variable.  This does mean that in the case where
        // the buffer was too small for a variable in the middle of the group, that
        // a smaller variable after it in the group may still be serialised into
        // the buffer.  Since that's a rare case it's not worth optimising for - in
        // either case this function will return a size greater than the buffer size
        // and the calling function will have to treat it as an error.
        //
        total_size += size;
        if (size <= resid) {
            // there was space for this one, account for it
            resid -= size;
            bp += size;
        }

        vp = vp->next_member();
    }
    return total_size;
}