PicoSoC - A simple example SoC using PicoRV32
=============================================

This is a simple PicoRV32 example design that can run code directly from an SPI
flash chip. This example design uses the Lattice iCE40-HX8K Breakout Board.

The flash is mapped to the memory region starting at 0x01000000. The reset
vector is set to 0x01100000, i.e. at the 1MB offset inside the flash memory.

A small scratchpad memory (default 256 words, i.e. 1 kB) is mapped to address
0x00000000.

Run `make test` to run the test bench (and create `testbench.vcd`).

Run `make prog` to build the configuration bit-stream and firmware images
and upload them to a connected iCE40-HX8K Breakout Board.

| File                          | Description                                                     |
| ----------------------------- | --------------------------------------------------------------- |
| [picosoc.v](picosoc.v)        | Top-level PicoSoC Verilog module                                |
| [picosoc.v](picosoc.v)        | Top-level PicoSoC Verilog module                                |
| [spimemio.v](spimemio.v)      | Memory controller that interfaces to external SPI flash         |
| [spiflash.v](spiflash.v)      | Simulation model of an SPI flash (used by testbench.v)          |
| [testbench.v](testbench.v)    | Simple test bench for the design (requires firmware.hex).       |
| [firmware.s](firmware.s)      | Assembler source for firmware.hex/firmware.bin.                 |
| [hx8kdemo.v](hx8kdemo.v)      | FPGA-based example implementation on iCE40-HX8K Breakout Board  |
| [hx8kdemo.pcf](hx8kdemo.pcf)  | Pin constraints for implementation on iCE40-HX8K Breakout Board |

### Memory map:

| Address Range            | Description                             |
| ------------------------ | --------------------------------------- |
| 0x00000000 .. 0x00FFFFFF | Internal SRAM                           |
| 0x01000000 .. 0x01FFFFFF | External Serial Flash                   |
| 0x02000000 .. 0x02000003 | SPI Flash Controller Config Register    |
| 0x03000000 .. 0x00FFFFFF | Memory mapped user peripherals          |

The example design (hx8kdemo.v) and generic test bench (testbench.v) have 32
GPIO pins mapped to the 32 bit word at address 0x03000000.

### SPI Flash Controller Config Register:

| Bit(s) | Description                                               |
| -----: | --------------------------------------------------------- |
|     31 | MEMIO Enable (reset=1, set to 0 to bit bang SPI commands) |
|  30:20 | Reserved (read 0)                                         |
|  19:16 | IO Output enable bits in bit bang mode                    |
|  15:14 | Reserved (read 0)                                         |
|     13 | Chip select (CS) line in bit bang mode                    |
|     12 | Serial clock line in bit bang mode                        |
|   11:8 | IO data bits in bit bang mode                             |
|      7 | Reserved (read 0)                                         |
|      6 | DDR Enable bit (reset=0)                                  |
|      5 | QSPI Enable bit (reset=0)                                 |
|      4 | Continous Read Enable bit (reset=0)                       |
|    3:0 | Number of QSPI dummy cycles (reset=0)                     |