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Explain seed argument to foboot-bitstream.py

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Update README to say what to do if the place-and-route process fails
to find an appropriate solution.
This commit is contained in:
Peter Chubb 2020-01-23 10:26:34 +11:00
parent be3dc254c5
commit 485d232563
1 changed files with 23 additions and 2 deletions
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25
README.md
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@ -23,11 +23,32 @@ To build the software, you need:
The hardware half will take care of building the software half, if it is run with `--boot-source bios` (which is the default). Therefore, to build Foboot, enter the `hw/` directory and run: The hardware half will take care of building the software half, if it is run with `--boot-source bios` (which is the default). Therefore, to build Foboot, enter the `hw/` directory and run:
``` ```
$ python3 foboot-bitstream.py --revision hacker $ python3 foboot-bitstream.py --revision hacker --seed 19
``` ```
This will verify you have the correct dependencies installed, compile the Foboot software, then synthesize the Foboot bitstream. The resulting output will be in `build/gateware/`. You should write `build/gateware/top-multiboot.bin` to your Fomu device in order to get basic bootloader support. This will verify you have the correct dependencies installed, compile the Foboot software, then synthesize the Foboot bitstream. The resulting output will be in `build/gateware/`. You should write `build/gateware/top-multiboot.bin` to your Fomu device in order to get basic bootloader support.
The `seed` argument is to set initial conditions for the
place-and-route phase. `nextpnr-ice40` uses a simulated annealing
algorithm that can result in one of several locally optimal layouts.
Only some of these will meet the timing requirements for Fomu.
If you see something like
```
ERROR: Max frequency for clock 'clk48_$glb_clk': 45.41 MHz (FAIL at 48.00 MHz)
```
try a different seed. You can search for an appropriate seed with:
```
for seed in $(seq 0 100)
do
python3 ./foboot-bitstream.py --revision pvt --seed $seed 2>&1 |
grep 'FAIL at 48.00 MHz' && continue
echo "Working Seed is $seed"
break
done
```
This can take a considerable time.
### Usage ### Usage
You can write the bitstream to your SPI flash. If you're using `fomu-flash`, you would run the following: You can write the bitstream to your SPI flash. If you're using `fomu-flash`, you would run the following:
@ -69,4 +90,4 @@ $ dfu-util -e
## Building the Software ## Building the Software
Software is contained in the `sw/` directory. Software is contained in the `sw/` directory.