Listens for SHM (Shared Memory) changes to send SHM data to the SPI port and from there to the your SPI devices's MISO. This is full configurable SPI listener. If want to write bytes to SPI port of RPi at high speed, write it to SHM (shared memory) with any programming language. The SPI service will detect changes and will read the modified memory (SHM) and write it to SPI.0 port. It will then write back the bytes returned from the device to SHM due to the nature of the SPI.
Configuration options stored in /etc/spi.service.conf as described below:
- PORT_COUNT = This is bit count to write SPI port at the same time. Default 96.
- LATCH_PIN = Optional. If your SPI hardware has latch pin (eq: 75HC595) you can define a GPIO pin. Default GPIO.22.
- LATCH_DELAY = Optional. You can set LATCH signal period as microseconds. Default 0.
- SPEED = SPI port speed as Hz. Default 40000.
- LOOP_DELAY_US = This is main loop delay. If you high detection speed on SHM you can decrease. Small values increase CPU loar. Default 100uS.
pi@raspberrypi:~ $ git clone https://github.com/enseitankado/spi-service.git
pi@raspberrypi:~ $ cd spi-service/
pi@raspberrypi:~/spi-service $./install.sh
Stopping spi.service...
Failed to stop spi.service: Unit spi.service not loaded.
Failed to kill unit spi.service: Unit spi.service not loaded.
Old binary removed.
Compiling from source code...
New binary created.
Old SystemD unit file removed.
Old configuration file removed.
New SystemD unit file installing...
New configuration file created at /etc/spi.service.conf with default settings.
Created symlink /etc/systemd/system/multi-user.target.wants/spi.service → /lib/systemd/system/spi.service.
The service is spi.service starting...
● spi.service - SHM (Shared Memory) listener for ss963 serial driver board and SPI driver
Loaded: loaded (/lib/systemd/system/spi.service; enabled; vendor preset: enabled)
Active: active (running) since Sun 2020-06-14 03:59:29 +03; 108ms ago
Main PID: 16818 (spiservice)
Tasks: 1 (limit: 2200)
Memory: 248.0K
CGroup: /system.slice/spi.service
└─16818 /usr/sbin/spiservice --port-count=96 --latch-pin=2 --latch-delay=0 --speed=4000000 --loop-delay-us=100
Haz 14 03:59:29 raspberrypi spiservice[16818]: SPI Port : 0
Haz 14 03:59:29 raspberrypi spiservice[16818]: STCP/LATCH pin : 2 (GPIO/BCM)
Haz 14 03:59:29 raspberrypi spiservice[16818]: STCP Delay : 0 uS
Haz 14 03:59:29 raspberrypi spiservice[16818]: SPI Speed : 4000000 Hz
Haz 14 03:59:29 raspberrypi spiservice[16818]: Loop Delay (uS) : 100 uS
Haz 14 03:59:29 raspberrypi spiservice[16818]: Port Count : 96
Haz 14 03:59:29 raspberrypi spiservice[16818]: Board Count : 1
Haz 14 03:59:29 raspberrypi spiservice[16818]: SHM_SEGMENT_ID : 1000146
Haz 14 03:59:29 raspberrypi spiservice[16818]: SHM Size : 1024 bytes/8192 ports
Haz 14 03:59:29 raspberrypi spiservice[16818]: Listening changes for first 12 bytes (96 ports) of SHM...
Finished.
Simply run unistall.sh
pi@raspberrypi:~ $ ./sp-service/uninstall.sh
SHM memory key (SHM_SEGMENT_ID) is 1000146 (0x000f42d2). You can read/write SHM with the key in any programming language. Remember: The service listen only (PORT_COUNT/8) byte for changes.
- To list SHM areas: ipcs -lm
- If you want delete SHM key: sudo ipcrm -M Maz SHM size is as default 1024 (You can drive 8194 port with it). Otherwise you can change this from def.c and run install.sh
Somethings about SPI writaback and --disable-write-back switch: Data that was in your buffer is overwritten by data returned from the SPI (MISO) bus.
The driver supports the following speeds:
cdiv speed
2 125.0 MHz
4 62.5 MHz
8 31.2 MHz
16 15.6 MHz
32 7.8 MHz
64 3.9 MHz
128 1953 kHz
256 976 kHz
512 488 kHz
1024 244 kHz
2048 122 kHz
4096 61 kHz
8192 30.5 kHz
16384 15.2 kHz
32768 7629 Hz
When asking for say 24 MHz, the actual speed will be 15.6 MHz.
- ref: projects.drogon.net/understanding-spi-on-the-raspberry-pi)
- ref: www.raspberrypi.org/documentation/hardware/raspberrypi/spi/README.md
You can also use spiservice as a command line tool while running service.
However, I recommend that you stop the service with the
sudo systemctl stop spi.service command to avoid logical confusion.
When using the spiservice tool from the command line, configuration in
/etc/spi.service.conf will be ommited.
You must use its own option for each setting as parameter.
You can give the parameters -h or --help to see the options.
pi@raspberrypi:~/spi-service $ spiservice -h
OPTIONS
-c, --console-mode
Enable console mode.
In console mode the outputs redirected to console instead of syslog.
-u, --show-updates
Used in console mode to print out SHM updates.
Printing updates to the console dramatically reduces SPI update speed.
Because of terminal screen refreshing very slow according to SPI peripheral.
-s, --speed <value>
SPI communication speed as Hertz (Hz).
Available rates are (as MHz): 0.5,1,2,4,8,16,32.
Default value is: 8000000 Hz
-g, --latch-pin <value>
Latch pin number as GPIO/BCM numbering.
Default value is: 0 and disabled.
-l, --latch-delay <value>
Latch signal width as microsecond.
Default value is: 0 uS
-p, --port-count <value>
Port count to drive. Port count must be a multiple of 96.
Default value is: 96
-d, --loop-delay-us <value>
SHM scanning delay as micro seconds (us).
With small values, SHM is read more often, whereas high CPU usage occurs.
Default value is: 100
-k, --shm-segment-key <value>
Key value of shm memory to monitor.
Key value must be decimal.
The data read back to the spi buffer is also written back to the SHM memory.
Default value is: 1000146
-w, --disable-shm-writeback <value>
As a default the SPI readback data written back to the SHM.
Use this key to disable write back if you want shm data to remain unchanged.
You can give a value other than 0 to enable this key.
Default value is: 1000146
Below command runs with service at the same time. I suggest firstly stop the service (sudo systemctl stop spi.service)
$ spiservice --console-mode --show-updates
SPI Port : 0
STCP/LATCH pin : 2 (GPIO/BCM)
STCP Delay : 0 uS
SPI Speed : 8000000 Hz
Loop Delay (uS) : 100 uS
Port Count : 96
Board Count : 1
SHM_SEGMENT_KEY : 1000146
SHM Size : 1024 bytes/8192 ports
SHM Writeback : Enabled
Listening changes for first 12 bytes (96 ports) of SHM...
To break press ^C
SHM (SHM_SEGMENT_KEY=1000146) updates monitoring.
Tx ( 0 Hz): 000000000000000000000000000000000000000000000010000000000000000000000000000000000000000000000000
Rx ( 0 Hz): 000000000000000000000000000000000000000000000010000000000000000000000000000000000000000000000000
74HC595'in frequency characteristic: Maximum clock pulse frequency for SH_CP or ST_CP:
Vcc Min Typ Max Unit
2.0 9 30 - MHz Typ. T:0,033 uSec = 33nS
4.5 30 91 - MHz
6.0 35 108 - MHz
Propagation delay Max. 220nS
At VDD=15V, ID=4.4A, VGS=10V and RG=6Ω PJA3406's switching limit: 10,75MHz
Turn-On Delay Time 3ns
Turn-On Rise Time 39ns
Turn-Off Delay Time 23ns
Turn-Off Fall Time 28ns
RPi Max. SPI Speed 32MHZ
Transmitted decimals: 1 2 4 8 16 32 64 128
My Clock Test (25.2.17)
CONFIG MEAUSURED CLOCK(MHz) EXEC TIME(uS)
~~~~~~~~ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ~~~~~~~~~~~~
SPISetup MOSTLY Min Max SPIDataRW Data Lost
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
0.1 0.05 0.05 0.05 ~65 0/8
0.5* 0.25 0.25 0.25 ~70 0/8
1* 0.5 0.5 0.5 ~70 0/8
2* 1 1 1 ~70 0/8
3 1.455 1.455 1.455 ~100 0/8
4* 2 2 2 ~80 0/8
5 2.66 2.28 2.66 ~75 0/8
6 3.2 2.66 3.2 ~68 0/8
7 4 3.2 4 ~65 0/8
8* 4 3.2 4 ~62 0/8
9 4 4 5.3 ~58 0/8
10 4.8 4.8 6 ~60 0/8
11 5.33 5.33 8 ~63 0/8
12 5.33 5.33 5.33 ~55 0/8
13 5.33 5.33 5.33 ~55 0/8
14 8 5.33 8 ~52 0/8
15 8 5.33 8 ~52 0/8
16* 8 6 8 ~55 1/8
20 8 5.33 8 ~50 7/8
24 4 5.33 4 ~49 7/8
32 8 8 12 ~50 0/8
40 4 2.6 5.3 ~45 7/8
48 3 3 8 ~47 7/8
If your device at the end of the SPI port has a Latch control, you can configure the spi service accordingly. The service sends the data of each SHM update to the device and can activate the latch line for the desired time. The pin and latch time to provide the latch function can be set via the configuration file. The connection diagram of a driver card with the visual latch function below appears. SPI service activates the latch pin after writing the bits to the card, and the bits are reflected in the outputs of the card. Latch function is normally not enabled. However, if a GPIO pin is assigned for the latch function, the service applies the latch signal for the STCP delay time.
