FETX

Simulation of Symmetrical FET Networks

The API provides methods for dynamically creating circuits or loading them from netlist files.

There are 2 structures that represent a circuit/network. The fetx_netlist structure can be directly translated from an input file or can be programmatically generated. The fetx_io structure contains run-time data and is initialised from the fetx_netlist structure.

make in the root directory will build the library.

Tests

make test will compile and run the tests.

Example Program

Example code using the library can be found in the examples/ directory. Example netlists can be found in the netlists/ directory, and vectors to exercise/test them can be found in the vectors/ directory.

make example will compile an example program which takes 0 or 2 arguments. If 0, it programmatically generates an inverter and exercises it, if 2 it reads a netlist from the file specified by the first argument, then exercises it with a vector from the file specified by the second argument.

$ ./bin/fetx_example ./netlists/nand.nl vectors/pg_2in.vct
0100
0101
0100
0110
0111
0101
0111
0110
0100

1
1
1
1
0
1
0
1

Limitations

FETX does not take into account complimentary pairs whose gates are not directly attached to one another. It also does not correctly resolve every circumstance where a FET is indirectly connected to its own gate.

Netlists

The fetx_netlist structure contains a list of FETs and associated inputs and outputs. The inputs, outputs and FET connections are specified as node indices.

enum fetx_fet_types {
  FETX_FET_N = 0,
  FETX_FET_P,
};

struct fetx_fetlist_fet {
  /* gate source drain, gate is connections[0] */
  size_t connections[3];
  enum fetx_fet_types type;
};

struct fetx_fetlist {
  struct fetx_fetlist_fet *fets;
  size_t size;
};

struct fetx_netlist {
  struct fetx_fetlist fl;
  size_t *inputs;
  size_t *outputs;
  size_t nodes_size;
  size_t inputs_size;
  size_t outputs_size;
};

Functions

void fetx_netlist_delete(struct fetx_netlist nl);

Deallocates the memory associated with the netlist nl.

enum fetx_errs fetx_netlist_new(struct fetx_netlist *const nl);

Allocates memory for the netlist nl based on it's inputs_size, outputs_size and fl.size members, all of which should be initialised before calling the function.

Returns (a combination of):

• FETX_ERR_ALLOC A memory allocation error occurred.
• FETX_ERR_NONE Netlist allocated successfully.

void fetx_netlist_assign_fet(struct fetx_netlist *const nl, const struct fetx_fetlist_fet fet, const size_t index);

Copies fet onto the netlist nl at index index.

void fetx_netlist_assign_input(struct fetx_netlist *const nl, const size_t node_index, const size_t index);

Assigns the node at node_index as an input and place it at position index in the input array of netlist nl.

void fetx_netlist_assign_output(struct fetx_netlist *const nl, const size_t node_index, const size_t index);

Assigns the node at node_index as an output and place it at position index in the output array of netlist nl.

void fetx_netlist_update_nodes_size(struct fetx_netlist *const nl);

After all the FETs have been assigned, this function can be called to work out the size of the node array, a necessary step before generating the fetx_io struct from nl. This can be done manually by setting the nodes_size member if the number is already known, it should be the largest node index + 1.

enum fetx_errs fetx_netlist_from_file(struct fetx_netlist *const nl, const char *const pathname);

Populates the netlist nl from the file at pathname, see below or the netlists/ directory for file formats.

Returns (a combination of):

• FETX_ERR_ALLOC A memory allocation error occurred.
• FETX_ERR_IO An input error occurred.
• FETX_ERR_FOPEN Failed to open file.
• FETX_ERR_FFORMAT Incorreect file format.
• FETX_ERR_FCLOSE Failed to close file.
• FETX_ERR_NONE Netlist read successfully.

enum fetx_errs fetx_netlist_to_file(const struct fetx_netlist nl, const char *const pathname);

Generates a file pathanme from the netlist nl, see below or the netlists/ directory for file formats.

Returns (a combination of):

• FETX_ERR_IO An output error occurred.
• FETX_ERR_FOPEN Failed to open file.
• FETX_ERR_FCLOSE Failed to close file.
• FETX_ERR_NONE Netlist written successfully.

enum fetx_errs fetx_netlist_print(const struct fetx_netlist nl);

Prints the netlist nl.

Returns (a combination of):

• FETX_ERR_IO An output error occurred.
• FETX_ERR_NONE Netlist written successfully.

Runtime

The fetx_io structure contains the runtime data along with associated inputs and outputs.

struct fetx_io {
  struct fetx fx;
  struct fetx_input_node *inputs;
  struct fetx_node **outputs;
  size_t inputs_size;
  size_t outputs_size;
};

Functions

void fetx_io_delete(struct fetx_io io);

Deallocates the memory associated with the runtime struct io.

int fetx_io_init(struct fetx_io *const io, const struct fetx_netlist nl);

Initialises the fetx_io struct io from the netlist nl. After calling this the netlist nl can be disposed of.

Returns -1 if there was a memory allocation error, 0 otherwise.

void fetx_io_input(struct fetx_io *const io, const size_t input_index, const enum fetx_node_states state);

Sets the state of the node at index input_index in the input array if io to state state.

enum fetx_node_states fetx_io_output(const struct fetx_io io, const size_t output_index);

Gets the state of the node at index output_index in the output array of io.

void fetx_io_inputs(struct fetx_io *const io, const enum fetx_node_states *const inputs);

Sets the state of all the nodes on the input array of io to the states in the inputs array.

void fetx_io_outputs(enum fetx_node_states *const outputs, const struct fetx_io io);

Gets the state of all the nodes on the output array of io and writes them to the outputs array.

unsigned char fetx_io_resolve(struct fetx_io *const io);

Once the inputs have been set to the desired states, this function will attempt to incrementally resolve the network. Note that some networks may oscillate indefinitely and never resolve.

Returns 1 when the network has resolved, otherwise 0.

File Formats

Netlists

All numbers are decimal node indexes, the FET connections are ordered gate, source, drain (although the source and drain are interchangeable).

Line Types

• i - input nodes
• o - output nodes
• p - p channel FET
• n - n channel FET

Example, a nand gate:

i 0 1 2 3
o 4
p 2 1 4
p 3 1 4
n 2 4 5
n 3 5 0

Vectors

Vectors are 2 dimensional arrays of node states that co-respond to the states of the input or output nodes of a netlist. They can be loaded from a file and are useful for running fixed tests.

State	File Representation
Low	0
High	1
Unstable low	2
Unstable high	3
Unstable multiple	4
Undriven	5

Each line represents states at a particular time instance.

Example, for exercising a 2 input gate:

01 00
01 01
01 00
01 10
01 11
01 01
01 11
01 10
01 00