Object Finders ============== .. contents:: :local: Introduction ------------ Object finders are an important part of the glue MAME provides to tie the devices that make up an emulated system together. Object finders are used to specify connections between devices, to efficiently access resources, and to check that necessary resources are available on validation. Object finders search for a target object by tag relative to a base device. Some types of object finder require additional parameters. Most object finders have required and optional versions. The required versions will raise an error if the target object is not found. This will prevent a device from starting or cause a validation error. The optional versions will log a verbose message if the target object is not found, and provide additional members for testing whether the target object was found or not. Object finder classes are declared in the header src/emu/devfind.h and have Doxygen format API documentation. Types of object finder ---------------------- required_device, optional_device Finds a device. The template argument ``DeviceClass`` should be a class derived from ``device_t`` or ``device_interface``. required_memory_region, optional_memory_region Finds a memory region, usually from ROM definitions. The target is the ``memory_region`` object. required_memory_bank, optional_memory_bank Finds a memory bank instantiated in an address map. The target is the ``memory_bank`` object. memory_bank_creator Finds a memory bank instantiated in an address map, or creates it if it doesn’t exist. The target is the ``memory_bank`` object. There is no optional version, because the target object will always be found or created. required_ioport, optional_ioport Finds an I/O port from a device’s input port definitions. The target is the ``ioport_port`` object. required_address_space, optional_address_space Finds a device’s address space. The target is the ``address_space`` object. required_region_ptr, optional_region_ptr Finds the base pointer of a memory region, usually from ROM definitions. The template argument ``PointerType`` is the target type (usually an unsigned integer type). The target is the first element in the memory region. required_shared_ptr, optional_shared_ptr Finds the base pointer of a memory share instantiated in an address map. The template argument ``PointerType`` is the target type (usually an unsigned integer type). The target is the first element in the memory share. memory_share_creator Finds the base pointer of a memory share instantiated in an address map, or creates it if it doesn’t exist. The template argument ``PointerType`` is the target type (usually an unsigned integer type). The target is the first element in the memory share. There is no optional version, because the target object will always be found or created. Finding resources ----------------- We’ll start with a simple example of a device that uses object finders to access its own child devices, inputs and ROM region. The code samples here are based on the Apple II Parallel Printer Interface card, but a lot of things have been removed for clarity. Object finders are declared as members of the device class:: class a2bus_parprn_device : public device_t, public device_a2bus_card_interface { public: a2bus_parprn_device(machine_config const &mconfig, char const *tag, device_t *owner, u32 clock); virtual void write_c0nx(u8 offset, u8 data) override; virtual u8 read_cnxx(u8 offset) override; protected: virtual tiny_rom_entry const *device_rom_region() const override; virtual void device_add_mconfig(machine_config &config) override; virtual ioport_constructor device_input_ports() const override; private: required_device m_printer_conn; required_device m_printer_out; required_ioport m_input_config; required_region_ptr m_prom; }; We want to find a ``centronics_device``, an ``output_latch_device``, an I/O port, and an 8-bit memory region. In the constructor, we set the initial target for the object finders:: a2bus_parprn_device::a2bus_parprn_device(machine_config const &mconfig, char const *tag, device_t *owner, u32 clock) : device_t(mconfig, A2BUS_PARPRN, tag, owner, clock), device_a2bus_card_interface(mconfig, *this), m_printer_conn(*this, "prn"), m_printer_out(*this, "prn_out"), m_input_config(*this, "CFG"), m_prom(*this, "prom") { } Each object finder takes a base device and tag as constructor arguments. The base device supplied at construction serves two purposes. Most obviously, the tag is specified relative to this device. Possibly more importantly, the object finder registers itself with this device so that it will be called to perform validation and object resolution. Note that the object finders *do not* copy the tag strings. The caller must ensure the tag string remains valid until after validation and/or object resolution is complete. The memory region and I/O port come from the ROM definition and input definition, respectively:: namespace { ROM_START(parprn) ROM_REGION(0x100, "prom", 0) ROM_LOAD( "prom.b4", 0x0000, 0x0100, BAD_DUMP CRC(00b742ca) SHA1(c67888354aa013f9cb882eeeed924e292734e717) ) ROM_END INPUT_PORTS_START(parprn) PORT_START("CFG") PORT_CONFNAME(0x01, 0x00, "Acknowledge latching edge") PORT_CONFSETTING( 0x00, "Falling (/Y-B)") PORT_CONFSETTING( 0x01, "Rising (Y-B)") PORT_CONFNAME(0x06, 0x02, "Printer ready") PORT_CONFSETTING( 0x00, "Always (S5-C-D)") PORT_CONFSETTING( 0x02, "Acknowledge latch (Z-C-D)") PORT_CONFSETTING( 0x04, "ACK (Y-C-D)") PORT_CONFSETTING( 0x06, "/ACK (/Y-C-D)") PORT_CONFNAME(0x08, 0x00, "Strobe polarity") PORT_CONFSETTING( 0x00, "Negative (S5-A-/X, GND-X)") PORT_CONFSETTING( 0x08, "Positive (S5-X, GND-A-/X)") PORT_CONFNAME(0x10, 0x10, "Character width") PORT_CONFSETTING( 0x00, "7-bit") PORT_CONFSETTING( 0x10, "8-bit") INPUT_PORTS_END } // anonymous namespace tiny_rom_entry const *a2bus_parprn_device::device_rom_region() const { return ROM_NAME(parprn); } ioport_constructor a2bus_parprn_device::device_input_ports() const { return INPUT_PORTS_NAME(parprn); } Note that the tags ``"prom"`` and ``"CFG"`` match the tags passed to the object finders on construction. Child devices are instantiated in the device’s machine configuration member function:: void a2bus_parprn_device::device_add_mconfig(machine_config &config) { CENTRONICS(config, m_printer_conn, centronics_devices, "printer"); m_printer_conn->ack_handler().set(FUNC(a2bus_parprn_device::ack_w)); OUTPUT_LATCH(config, m_printer_out); m_printer_conn->set_output_latch(*m_printer_out); } Object finders are passed to device types to provide tags when instantiating child devices. After instantiating a child device in this way, the object finder can be used like a pointer to the device until the end of the machine configuration member function. Note that to use an object finder like this, its base device must be the same as the device being configured (the ``this`` pointer of the machine configuration member function). After the emulated machine has been started, the object finders can be used in much the same way as pointers:: void a2bus_parprn_device::write_c0nx(u8 offset, u8 data) { ioport_value const cfg(m_input_config->read()); m_printer_out->write(data & (BIT(cfg, 8) ? 0xffU : 0x7fU)); m_printer_conn->write_strobe(BIT(~cfg, 3)); } u8 a2bus_parprn_device::read_cnxx(u8 offset) { offset ^= 0x40U; return m_prom[offset]; } For convenience, object finders that target the base pointer of memory regions and shares can be indexed like arrays. Connections between devices --------------------------- Devices need to be connected together within a system. For example the Sun SBus device needs access to the host CPU and address space. Here’s how we declare the object finders in the device class (with all distractions removed):: DECLARE_DEVICE_TYPE(SBUS, sbus_device) class sbus_device : public device_t, public device_memory_interface { template sbus_device( machine_config const &mconfig, char const *tag, device_t *owner, u32 clock, T &&cpu_tag, U &&space_tag, int space_num) : sbus_device(mconfig, tag, owner, clock) { set_cpu(std::forward(cpu_tag)); set_type1space(std::forward(space_tag), space_num); } sbus_device(machine_config const &mconfig, char const *tag, device_t *owner, u32 clock) : device_t(mconfig, type, tag, owner, clock), device_memory_interface(mconfig, *this), m_maincpu(*this, finder_base::DUMMY_TAG), m_type1space(*this, finder_base::DUMMY_TAG, -1) { } template void set_cpu(T &&tag) { m_maincpu.set_tag(std::forward(tag)); } template void set_type1space(T &&tag, int num) { m_type1space.set_tag(std::forward(tag), num); } protected: required_device m_maincpu; required_address_space m_type1space; }; There are several things to take note of here: * Object finder members are declared for the things the device needs to access. * The device doesn’t know how it will fit into a larger system, the object finders are constructed with dummy arguments. * Configuration member functions are provided to set the tag for the host CPU, and the tag and index for the type 1 address space. * In addition to the standard device constructor, a constructor with additional parameters for setting the CPU and type 1 address space is provided. The constant ``finder_base::DUMMY_TAG`` is guaranteed to be invalid and will not resolve to an object. This makes it easy to detect incomplete configuration and report an error. Address spaces are numbered from zero, so a negative address space number is invalid. The member functions for configuring object finders take a universal reference to a tag-like object (templated type with ``&&`` qualifier), as well as any other parameters needed by the specific type of object finder. An address space finder needs an address space number in addition to a tag-like object. So what’s a tag-like object? Three things are supported: * A C string pointer (``char const *``) representing a tag relative to the device being configured. Note that the object finder will not copy the string. The caller must ensure it remains valid until resolution and/or validation is complete. * Another object finder. The object finder will take on its current target. * For device finders, a reference to an instance of the target device type, setting the target to that device. Note that this will not work if the device is subsequently replaced in the machine configuration. It’s most often used with ``*this``. The additional constructor that sets initial configuration delegates to the standard constructor and then calls the configuration member functions. It’s purely for convenience. When we want to instantiate this device and hook it up, we do this:: SPARCV7(config, m_maincpu, 20'000'000); ADDRESS_MAP_BANK(config, m_type1space); SBUS(config, m_sbus, 20'000'000); m_sbus->set_cpu(m_maincpu); m_sbus->set_type1space(m_type1space, 0); We supply the same object finders to instantiate the CPU and address space devices, and to configure the SBus device. Note that we could also use literal C strings to configure the SBus device, at the cost of needing to update the tags in multiple places if they change:: SBUS(config, m_sbus, 20'000'000); m_sbus->set_cpu("maincpu"); m_sbus->set_type1space("type1", 0); If we want to use the convenience constructor, we just supply additional arguments when instantiating the device:: SBUS(config, m_sbus, 20'000'000, m_maincpu, m_type1space, 0); Object finder arrays -------------------- Many systems have multiple similar devices, I/O ports or other resources that can be logically organised as an array. To simplify these use cases, object finder array types are provided. The object finder array type names have ``_array`` added to them: +------------------------+------------------------------+ | required_device | required_device_array | +------------------------+------------------------------+ | optional_device | optional_device_array | +------------------------+------------------------------+ | required_memory_region | required_memory_region_array | +------------------------+------------------------------+ | optional_memory_region | optional_memory_region_array | +------------------------+------------------------------+ | required_memory_bank | required_memory_bank_array | +------------------------+------------------------------+ | optional_memory_bank | optional_memory_bank_array | +------------------------+------------------------------+ | memory_bank_creator | memory_bank_array_creator | +------------------------+------------------------------+ | required_ioport | required_ioport_array | +------------------------+------------------------------+ | optional_ioport | optional_ioport_array | +------------------------+------------------------------+ | required_address_space | required_address_space_array | +------------------------+------------------------------+ | optional_address_space | optional_address_space_array | +------------------------+------------------------------+ | required_region_ptr | required_region_ptr_array | +------------------------+------------------------------+ | optional_region_ptr | optional_region_ptr_array | +------------------------+------------------------------+ | required_shared_ptr | required_shared_ptr_array | +------------------------+------------------------------+ | optional_shared_ptr | optional_shared_ptr_array | +------------------------+------------------------------+ A common case for an object array finder is a key matrix:: class keyboard_base : public device_t, public device_mac_keyboard_interface { protected: keyboard_base(machine_config const &mconfig, device_type type, char const *tag, device_t *owner, u32 clock) : device_t(mconfig, type, tag, owner, clock), device_mac_keyboard_interface(mconfig, *this), m_rows(*this, "ROW%u", 0U) { } u8 bus_r() { u8 result(0xffU); for (unsigned i = 0U; m_rows.size() > i; ++i) { if (!BIT(m_row_drive, i)) result &= m_rows[i]->read(); } return result; } required_ioport_array<10> m_rows; }; Constructing an object finder array is similar to constructing an object finder, except that rather than just a tag you supply a tag format string and index offset. In this case, the tags of the I/O ports in the array will be ``ROW0``, ``ROW1``, ``ROW2``, … ``ROW9``. Note that the object finder array allocates dynamic storage for the tags, which remain valid until destruction. The object finder array is used in much the same way as a ``std::array`` of the underlying object finder type. It supports indexing, iterators, and range-based ``for`` loops. Because an index offset is specified, the tags don’t need to use zero-based indices. It’s common to use one-based indexing like this:: class dooyong_state : public driver_device { protected: dooyong_state(machine_config const &mconfig, device_type type, char const *tag) : driver_device(mconfig, type, tag), m_bg(*this, "bg%u", 1U), m_fg(*this, "fg%u", 1U) { } optional_device_array m_bg; optional_device_array m_fg; }; This causes ``m_bg`` to find devices with tags ``bg1`` and ``bg2``, while ``m_fg`` finds devices with tags ``fg1`` and ``fg2``. Note that the indexes into the object finder arrays are still zero-based like any other C array. It’s also possible to other format conversions, like hexadecimal (``%x`` and ``%X``) or character (``%c``):: class eurit_state : public driver_device { public: eurit_state(machine_config const &mconfig, device_type type, char const *tag) : driver_device(mconfig, type, tag), m_keys(*this, "KEY%c", 'A') { } private: required_ioport_array<5> m_keys; }; In this case, the key matrix ports use tags ``KEYA``, ``KEYB``, ``KEYC``, ``KEYD`` and ``KEYE``. When the tags don’t follow a simple ascending sequence, you can supply a brace-enclosed initialiser list of tags:: class seabattl_state : public driver_device { public: seabattl_state(machine_config const &mconfig, device_type type, char const *tag) : driver_device(mconfig, type, tag), m_digits(*this, { "sc_thousand", "sc_hundred", "sc_half", "sc_unity", "tm_half", "tm_unity" }) { } private: required_device_array m_digits; };