tillitis-key/hw/application_fpga/core/uart

uart

A simple universal asynchronous receiver/transmitter (UART) core implemented in Verilog. The core is completed and has been used in several FPGA designs.

Introduction

The UART core is used as main communication channel between the TKey device System on Chip (SoC) and the TKey client. The UART contains a 512 byte receive buffer, allowing the SW running on the SoC to not have to wait for bytes and poll them as soon as they are received. The number of bytes in the FIFO is also exposed to the SW through the ADDR_RX_BYTES address.

The number of data and stop bits can be configured prior to building the core.

The bit rate can also be configured prior to building the core. It should be based on the target clock frequency divided by the bit rate in order to hit the center of the bits. For example, a clock of 18 MHz and a target bit rate of 62500 bps yields: Divisor = 18E6 / 62500 = 288

The UART core includes hardware flow control in the form of two CTS lines. One input that the core will check before sending bytes, and one output to signal to a connected device that the internal FIFO is full. The CTS are active-low.

API

ADDR_RX_STATUS: 0x20
ADDR_RX_DATA:   0x21
ADDR_RX_BYTES:  0x22

ADDR_TX_STATUS: 0x40
ADDR_TX_DATA:   0x41

Implementation notes.

The FIFO allocates a single block RAM (EBR).