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Update PicoSoC README

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Clifford Wolf 2017-09-21 19:58:55 +02:00
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@ -5,13 +5,20 @@ PicoSoC - A simple example SoC using PicoRV32
![](overview.svg)
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.
flash chip. It can be used as a turn-key solution for simple control tasks in
ASIC and FPGA designs.
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.
An example implementation targeting the Lattice iCE40-HX8K Breakout Board is
included.
A small scratchpad memory (default 256 words, i.e. 1 kB) is mapped to address
0x00000000.
The flash is mapped to the memory regions starting at 0x00000000 and
0x01000000, with the SRAM overlayed for the mapping at 0x00000000. The SRAM
is just a small scratchpad memory (default 256 words, i.e. 1 kB).
The reset vector is set to 0x00100000, i.e. at 1MB into in the flash memory.
See the included demo firmware and linker script for how to build a firmware
image for this system.
Run `make test` to run the test bench (and create `testbench.vcd`).
@ -46,8 +53,11 @@ physical SRAM will read from the corresponding addresses in serial flash.
Reading from the UART Send/Recv Data Register will return the last received
byte, or -1 (all 32 bits set) when the receive buffer is empty.
The example design (hx8kdemo.v) and generic test bench (testbench.v) have 32
GPIO pins mapped to the 32 bit word at address 0x03000000.
The UART Clock Divider Register must be set to the system clock freuqency
divided by the baud rate.
The example design (hx8kdemo.v) has the 8 LEDs on the iCE40-HX8K Breakout Board
mapped to the low byte of the 32 bit word at address 0x03000000.
### SPI Flash Controller Config Register:
@ -89,3 +99,9 @@ For Quad I/O mode the QUAD flag in CR1V must be set before enabling Quad I/O in
SPI master. Either set it by writing the corresponding bit in CR1NV once, or by writing
it from your device firmware at every bootup. (See `set_flash_qspi_flag()` in
`firmware.c` for an example for the latter.)
Note that some changes to the Lattice iCE40-HX8K Breakout Board are required to support
the faster configurations: (1) The flash chip must be replaced with one that supports the
faster read commands and (2) the IO2 and IO3 pins on the flash chip must be connected to
the FPGA IO pins T9 and T8 (near the center of J3).