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
FPGA board.
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
presented as GPIO[16]
(which was previously unused).
The example commands assume $REPO_TOP
is set to the toplevel directory
of the repo.
Setup
If packages have not previously been installed you will need to set a
few things up. First use apt
and 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 --flippy
or -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
4-byte message.
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
messages.
$ cd $REPO_TOP/util/simplespi
$ ./spitest.py -l 120