Simple SPI Tests
spitest is a trivial Python tool for interacting with the SPI device
code in the
hello_world test program running on
top_earlgrey on the
The same FTDI interface is used for SPI as for JTAG, so this tool
cannot be used at the same time as an OpenOCD debugger. The
top_earlgray_nexsysvideo pin mux has been modified to use one of the
FTDI GPIOs to select between the two interfaces, so it is possible to
dynamically switch between the tools. This status bit is also
GPIO (which was previously unused).
The example commands assume
$REPO_TOP is set to the toplevel directory
of the repo.
If packages have not previously been installed you will need to set a
few things up. First use
pip3 to install some required packages:
$ sudo apt-get install libusb-1.0 $ pip3 install --user pyftdi
You also need the
udev rules to be set correctly by following the
instructions for setting up the Xilinx tools.
SPI/JTAG selection GPIO
The tool can be used to test the SPI/JTAG selection gpio. This is done
by providing the
-f argument which causes the
selection to be flipped 10 times with 2 second pauses between. The
hello_world program will see the bit flip and print a message.
$ cd $REPO_TOP/util/simplespi $ ./spitest.py -f
SPI Protocol Test
The SPI protocol used in the test is a simple exchange of 4-byte
messages. When data is received from the SPI Device interface the
hello_world program will receive and print it out on the UART. The
first four bytes have their bottom bit inverted and are returned in
the next SPI transaction. If the sender is faster than the FPGA then
messages are aggregated in the receive buffer and will appear as a
single long message to
hello_world which will only return a single
A simple test should therefore just use 4 characters.
$ cd $REPO_TOP/util/simplespi $ ./spitest.py 1234 $ ./spitest.py 5678
Long messages will be padded to a multiple of 4 bytes before being sent, and there may be some garbage return messages.
$ cd $REPO_TOP/util/simplespi $ ./spitest.py the quick brown fox jumps
Messages of any length (the length given is used even if not a
multiple of 4) may be generated by the tool. The message is formed
from repeating the ascii characters
0123456789abcdef (to fill the
required length) and sent, and there may be some garbage return
$ cd $REPO_TOP/util/simplespi $ ./spitest.py -l 120