Note: This driver will not be compiled into images aimed at non-ARM CPUS. It is only really intended to work on the Raspberry Pi. It may, or may not, work on similar boards or direct clones.

1. Purpose

This driver allows the use of the Rapberry Pi GPIO pins in a way analagous to the parallel port driver on x86 PCs. It can use the same step generators, encoder counters and similar components.

2. Bruk

loadrt hal_pi_gpio dir=0x13407 exclude=0x1F64BF8

The "dir" mask determines whether the pins are inputs and outputs, the exclude mask prevents the driver from using the pins (and so allows them to be used for their normal RPi purposes such as SPI or UART).

The mask can be in decimal or hexadecimal (hex may be easier as there will be no carries).

To determine the value of the masks, add up the hex/decimal values for all pins that should be configured as output, and analogously for all pins that should be excluded according to the following table.

Table 1. GPIO masks - mapping of GPIO numbers (leftmost column) to physical pin numbers as printed on the Raspberry Pi board (rightmost column) and the decimal/hexadecimal values that contribute to the value of the mask.
GPIO Num Decimal Hex Pin Num

2

1

0x00000001

3

3

2

0x00000002

5

4

4

0x00000004

7

5

8

0x00000008

29

6

16

0x00000010

31

7

32

0x00000020

26

8

64

0x00000040

24

9

128

0x00000080

21

10

256

0x00000100

19

11

512

0x00000200

23

12

1024

0x00000400

32

13

2048

0x00000800

33

14

4096

0x00001000

8

15

8192

0x00002000

10

16

16384

0x00004000

36

17

32768

0x00008000

11

18

65536

0x00010000

12

19

131072

0x00020000

35

20

262144

0x00040000

38

21

524288

0x00080000

40

22

1048576

0x00100000

15

23

2097152

0x00200000

16

24

4194304

0x00400000

18

25

8388608

0x00800000

22

26

16777216

0x01000000

37

27

33554432

0x02000000

13

Note: In the calculation of the individual pin’s mask value its GPIO numbers are used, the value being derived as 2^(GPIO number - 2), whereas in the naming of the HAL pins it is the Raspberry Pi header pin numbers.

So, for example, if you enable GPIO 17 as an output (dir=0x8000) then that output will be controlled by the hal pin hal_pi_gpio.pin-11-out.

3. Pins

  • hal_pi_gpio.pin-NN-out

  • hal_pi_gpio.pin-NN-in

Depending on the dir and exclude masks.

4. Parametre

Only the standard timing parameters which are created for all components exist.

*hal_pi_gpio.read.tmax *hal_pi_gpio.read.tmax-increased *hal_pi_gpio.write.tmax *hal_pi_gpio.write.tmax-increased

For unknown reasons the driver also creates HAL pins to indicate timing

*hal_pi_gpio.read.time *hal_pi_gpio.write.time

5. Funksjoner

  • hal_pi_gpio.read - Add this to the base thread to update the HAL pin values to match the physical input values.

  • hal_pi_gpio.write - Add this to the base thread to update the physical pins to match the HAL values.

Typically the read function will be early in the call list, before any encoder counters and the write function will be later in the call list, after stepgen.make-pulses.

6. Pin Numbering

The GPIO connector and the pinout has been consistent since around 2015. These older Pi models are probably a poor choice for LinuxCNC anyway. However, this driver is designed to work with them, and will detect and correctly configure for the two alternative pinouts.

The current pinout mapping between GPIO numbers and connector pin numbers is included in the table above.

Note that the config string uses GPIO numbers, but once the driver is loaded the HAL pin names refer to connector pin numbers.

This may be more logical than it first appears. When setting up you need to configure enough pins of each type, whilst avoiding overwriting any other functions that your system needs. Then once the driver is loaded, in the HAL layer you just want to know where to connect the wires for each HAL pin.

7. Known Bugs

At the moment (2023-07-16) this driver only seems to work on Raspbian as the generic Debian image does not set up the correct interfaces in /dev/gpiomem and restricts access to the /sys/mem interface.