462 FazyRV-ExoTiny
462 : FazyRV-ExoTiny
- Author: Meinhard Kissich
- Description: A minimal SoC based on FazyRV that uses external QSPI ROM and RAM.
- GitHub repository
- GDS submitted
- HDL project
- Extra docs
- Clock: 50000000 Hz
How it works
This TinyTapeout implements a System-on-Chip (SoC) design based on the FazyRV RISC-V core. Documentation on the SoC can be found in github.com/meiniKi/FazyRV-ExoTiny. For details on the FazyRV core, please refer to github.com/meiniKi/FazyRV.
Features
- Instantiates FazyRV with a chunk size of 2 bits.
- Uses external instruction memory (QSPI ROM) and external data memory (QSPI RAM).
- Provides 6 memory-mapped general-purpose outputs and 7 inputs.
- Provides an SPI peripheral with programmable CPOL and a buffer of up to 4 bytes.
Pinout Overview
The overview shows the pinout for the TinyTapeout Demo PCB. A detailed description of the pins is given below.
Block Diagram
The block diagram outlines the on-chip peripherals and related addresses.
How to test
Once the design is enabled and released from reset, it first enables Quad Mode in the RAM. The Wishbone accesses are converted into QSPI transfers to exchange data. The first read from ROM (boot address: 0x00000000) enabled Continuous Mode to reduce the latency. To get started, you can flash the demo firmware in FazyRV-ExoTiny/demo. See the repo for more information.
Important: rst_n is not synchronized. Make sure it is released sufficient hold time after the rising clock edge and sufficient setup time before the falling edge. Do not release reset while clk is low. The design appears to be on the edge of implementability. An additional dff breaks convergence.
External hardware
- QSPI ROM: W25Q128JV or compatible
- QSPI RAM: APS6404L-3SQR or compatible
The design uses external ROM (Flash) and external RAM. All bus accesses in these regions are converted to QSPI transfers to read data from the ROM or to read/write data from/to the RAM, respectively. Alternatively, you can synthesize a model in an FPGA and attach it to the BIDIR PMOD header.
IO
| # | Input | Output | Bidirectional |
|---|---|---|---|
| 0 | General purpose input (GPI) 0. | General purpose output (GPO) 0. | QSPI ROM chip select (low active). |
| 1 | General purpose input (GPI) 1. | General purpose output (GPO) 1. | QSPI ROM/RAM SDO[0]. |
| 2 | General purpose input (GPI) 2. | General purpose output (GPO) 2. | QSPI ROM/RAM SDO[1]. |
| 3 | General purpose input (GPI) 3. | General purpose output (GPO) 3. | QSPI ROM/RAM SCK. |
| 4 | General purpose input (GPI) 4. | General purpose output (GPO) 4. | QSPI ROM/RAM SDO[2]. |
| 5 | General purpose input (GPI) 5. | General purpose output (GPO) 5. | QSPI ROM/RAM SDO[3]. |
| 6 | General purpose input (GPI) 6. | (User) SPI SCK. | QSPI RAM chip select (low active). |
| 7 | (User) SPI SDI. | (User) SPI SDO. | NC. |