Parallel Port Driver
The hal_parport component is a driver for the traditional PC parallel port. The port has a total of 17 physical pins. The original parallel port divided those pins into three groups: data, control, and status. The data group consists of 8 output pins, the control group consists of 4 pins, and the status group consists of 5 input pins.
In the early 1990’s, the bidirectional parallel port was introduced, which allows the data group to be used for output or input. The HAL driver supports the bidirectional port, and allows the user to set the data group as either input or output. If configured as out, a port provides a total of 12 outputs and 5 inputs. If configured as in, it provides 4 outputs and 13 inputs.
In some parallel ports, the control group pins are open collectors, which may also be driven low by an external gate. On a board with open collector control pins. If configured as x, it provides 8 outputs, and 9 inputs.
In some parallel ports, the control group has push-pull drivers and cannot be used as an input.
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Note
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HAL and Open Collectors
HAL cannot automatically determine if the x mode bidirectional pins are actually open collectors (OC). If they are not, they cannot be used as inputs, and attempting to drive them LOW from an external source can damage the hardware. To determine whether your port has open collector pins, load hal_parport in x mode. With no device attached, HAL should read the pin as TRUE. Next, insert a 470 ohm resistor from one of the control pins to GND. If the resulting voltage on the control pin is close to 0V, and HAL now reads the pin as FALSE, then you have an OC port. If the resulting voltage is far from 0V, or HAL does not read the pin as FALSE, then your port cannot be used in x mode. The external hardware that drives the control pins should also use open collector gates (e.g., 74LS05). On some computers, BIOS settings may affect whether x mode can be used. SPP mode is most likely to work. |
No other combinations are supported, and a port cannot be changed from input to output once the driver is installed.
The parport driver can control up to 8 ports (defined by MAX_PORTS in hal_parport.c). The ports are numbered starting at zero.
1. Loading
The hal_parport driver is a real time component so it must be loaded into the real time thread with loadrt. The configuration string consists of at least one port index or port address and optional pin direction specifiers. If the configuration string does not contain at least one address, it is an error.
loadrt hal_parport cfg="configuration string"
I/O addresses below 16 are treated as port indexes. This is the simplest way to install the parport driver and cooperates with the Linux parport_pc driver if it is loaded. This will use the address Linux has detected for parport 0.
loadrt hal_parport cfg="0"
The port address is specified using the hex notation 0x then the address.
loadrt hal_parport cfg="0x378"
The direction is in, out, or x and that determines the direction of the physical pins of the parallel port. If the direction is not specified, the default is out.
loadrt hal_parport cfg="0 in"
| Pin | in | out | x |
|---|---|---|---|
1 |
out |
out |
in |
2 |
in |
out |
out |
3 |
in |
out |
out |
4 |
in |
out |
out |
5 |
in |
out |
out |
6 |
in |
out |
out |
7 |
in |
out |
out |
8 |
in |
out |
out |
9 |
in |
out |
out |
10 |
in |
in |
in |
11 |
in |
in |
in |
12 |
in |
in |
in |
13 |
in |
in |
in |
14 |
in |
out |
in |
15 |
in |
in |
in |
16 |
out |
out |
in |
17 |
out |
out |
in |
You must also direct LinuxCNC to run the read and write functions.
addf parport.0.read base-thread addf parport.0.write base-thread
2. PCI Port Address
One good PCI parport card is made with the Netmos 9815 chipset. It has good +5V signals, and can come in a single or dual ports.
To find the I/O addresses for PCI cards open a terminal window and use the list pci command:
lspci -v
Look for the entry with "Netmos" in it. Example of a 2-port card:
0000:01:0a.0 Communication controller: \
Netmos Technology PCI 9815 Multi-I/O Controller (rev 01)
Subsystem: LSI Logic / Symbios Logic 2POS (2 port parallel adapter)
Flags: medium devsel, IRQ 5
I/O ports at b800 [size=8]
I/O ports at bc00 [size=8]
I/O ports at c000 [size=8]
I/O ports at c400 [size=8]
I/O ports at c800 [size=8]
I/O ports at cc00 [size=16]
From experimentation, I’ve found the first port (the on-card port) uses the third address listed (c000), and the second port (the one that attaches with a ribbon cable) uses the first address listed (b800). The following example shows the onboard parallel port and a PCI parallel port using the default out direction.
loadrt hal_parport cfg="0x378 0xc000"
Please note that your values will differ. The Netmos cards are Plug-N-Play, and might change their settings depending on which slot you put them into, so if you like to 'get under the hood' and re-arrange things, be sure to check these values before you start LinuxCNC.
3. Pins
-
parport.<p>.pin-<n>-out (bit) Drives a physical output pin.
-
parport.<p>.pin-<n>-in (bit) Tracks a physical input pin.
-
parport.<p>.pin-<n>-in-not (bit) Tracks a physical input pin, but inverted.
For each pin, <p> is the port number, and <n> is the physical pin number in the 25 pin D-shell connector.
For each physical output pin, the driver creates a single HAL pin, for example: parport.0.pin-14-out.
For each physical input pin, the driver creates two HAL pins, for example: parport.0.pin-12-in and parport.0.pin-12-in-not.
The -in HAL pin is TRUE if the physical pin is high, and FALSE if the physical pin is low. The -in-not HAL pin is inverted and is FALSE if the physical pin is high.
4. Parameters
-
parport.<p>.pin-<n>-out-invert (bit) Inverts an output pin.
-
parport.<p>.pin-<n>-out-reset (bit) (only for out pins) TRUE if this pin should be reset when the -reset function is executed.
-
parport.<p>.reset-time' (U32) The time (in nanoseconds) between a pin is set by write and reset by the reset function if it is enabled.
The -invert parameter determines whether an output pin is active high or active low. If -invert is FALSE, setting the HAL -out pin TRUE drives the physical pin high, and FALSE drives it low. If -invert is TRUE, then setting the HAL -out pin TRUE will drive the physical pin low.
5. Functions
-
parport.<p>.read (funct) Reads physical input pins of port <portnum> and updates HAL -in and -in-not pins.
-
parport.read-all (funct) Reads physical input pins of all ports and updates HAL -in and -in-not pins.
-
parport.<p>.write (funct) Reads HAL -out pins of port <p> and updates that port’s physical output pins.
-
parport.write-all (funct) Reads HAL -out pins of all ports and updates all physical output pins.
-
parport.<p>.reset (funct) Waits until reset-time has elapsed since the associated write, then resets pins to values indicated by -out-invert and -out-invert settings. reset must be later in the same thread as write. 'If '-reset is TRUE, then the reset function will set the pin to the value of -out-invert. This can be used in conjunction with stepgen’s doublefreq to produce one step per period. The stepgen stepspace for that pin must be set to 0 to enable doublefreq.
The individual functions are provided for situations where one port needs to be updated in a very fast thread, but other ports can be updated in a slower thread to save CPU time. It is probably not a good idea to use both an -all function and an individual function at the same time.
6. Common problems
If loading the module reports
insmod: error inserting '/home/jepler/emc2/rtlib/hal_parport.ko': -1 Device or resource busy
then ensure that the standard kernel module parport_pc is not
loaded
[In the LinuxCNC packages for Ubuntu, the file
/etc/modprobe.d/emc2
generally prevents parport_pc from being automatically loaded.]
and that no other device in the system has claimed the I/O ports.
If the module loads but does not appear to function, then the port address is incorrect.
7. Using DoubleStep
To setup DoubleStep on the parallel port you must add the function parport.n.reset after parport.n.write and configure stepspace to 0 and the reset time wanted. So that step can be asserted on every period in HAL and then toggled off by parport after being asserted for time specificed by parport.n.reset-time.
For example:
loadrt hal_parport cfg="0x378 out" setp parport.0.reset-time 5000 loadrt stepgen step_type=0,0,0 addf parport.0.read base-thread addf stepgen.make-pulses base-thread addf parport.0.write base-thread addf parport.0.reset base-thread addf stepgen.capture-position servo-thread ... setp stepgen.0.steplen 1 setp stepgen.0.stepspace 0
More information on DoubleStep can be found on the wiki.