clock_generator/README.md

# Clock Generator [![status-badge](https://ci.onders.org/api/badges/finga/clock_generator/status.svg)](https://ci.onders.org/finga/clock_generator)

The "Clock Generator" generates up to three different clock signals
between 15kHz and 162MHz.

Though, the board is not limited to this, it is designed to also be
usable for other applications.

## Board
The board is populated with an ATmega328p, an LCD and its backlight
driver, a rotary encoder which is also a push button and is powered
via mini USB. The TWI port of the ATmega interfaces the Si5351 which
is also driven from VCC and GND, a pin breakout for all unused pins
and some more VCC and GND pins as well as an ICSP header.

The general supply voltage behind the LDO regulator is 3.3V

Note that in the PCB layout the display and the rotary encoder are
placed on the backside of the PCB.

### ATmega328p
The Atmega328p is programmable via the ICSP header and is the center
piece of the board. All free pins can be used with J3 and the TWI with
J4.

#### Connectors
##### Breakout (J3)
| Pin left | ATmega328p | ATmega328p | Pin right |
|----------|------------|------------|-----------|
| 1        | +3.3V      | +3.3V      | 2         |
| 3        | PC1        | PD2        | 4         |
| 5        | PC2        | PD3        | 6         |
| 7        | PC3        | PD4        | 8         |
| 9        | PD0        | PD6        | 10        |
| 11       | PD1        | PD7        | 12        |
| 13       | GND        | GND        | 14        |

##### TWI (J4)
| Pin | Signal |
|-----|--------|
| 1   | +3.3V  |
| 2   | GND    |
| 3   | SDA    |
| 4   | SCL    |

### Si5351
The Si5351 is capable of generating three 8kHz to 160MHz clock
signals.

Internally, the Si5351 consists out of two phase locked loops which
feed three parallel and independently configurable clock synthesizers.

### Display
The DOGS102 graphic LCD module is controlled by SPI (Serial Peripheral
Interface) and the RST (reset) and CD (control data/display data)
pins. The contrast can be configured on the setup screen and its value
is stored in the EEPROM (Electrically Erasable Programmable Read-Only
Memory) of the ATmega.

#### Backlight
To drive the backlight, the Timer/Counter0 from the ATmega are used to
generate a PWM (Pulse Width Modulation) signal. This enables the
backlight to be variably bright. The brightness can also be configured
on the setup screen, and is stored inside the EEPROM.

### Rotary Encoder
To control the Clock Generator a single rotary encoder which is also a
push button is used.

## Firmware/Programming
Currently, there are two different implementations of the
firmware. The older one which is written in C and is not finished, and
the newer one which is in an early but functioning state and written
in Rust.

Note that mostly due to the display, the supply voltage after the LDO
regulator is 3.3V.

### The Rust Firmware
To flash the firmware, connect the ICSP pins of the board to the
programmer and inside the `firmware/rust/` directory run `cargo make
--profile release all`. This compiles the firmware with the release
profile, burns the fuses, writes the default configuration values to
the EEPROM and flashes the firmware.