This repository contains the source code to the parport_sphat driver which supports Elesar's Raspberry Pi serial and parallel port HAT (EA-981-8) under Linux.
Precompiled versions of this code can be downloaded by running the script which is held in the HAT's on board EEPROM:
bash /proc/device-tree/hat/custom_0
If you want to make changes to the driver or build your own module for a kernel version not supported by Elesar then you should use these sources as a starting point. The S&P HAT Quick Start Guide provided with the hardware explains how to subsequently load the modules.
With the modules loaded, a new character device appears as
/dev/lp0
which, with a suitable parallel printer, will accept print jobs in the usual manner.
One convenient way to get the sources which correspond to the kernerl and firmware which are currently running on your Pi is to use rpi-source available from this repository. Having downloaded that type:
rpi-source
In turn, this downloads the appropriate snapshot of the Linux source code.
By default parallel port support is not enabled on the Raspberry Pi. To enable:
cd linux
make menuconfig
When the interactive menu is displayed, enable the following 3 modules:
Device Drivers > Parallel port support
Device Drivers > Parallel port support > AX88796
Character Devices > Parallel printer support
by pressing 'M' next to the respective menu item. Note that the AX88796 driver only needs to be enabled in order to ensure CONFIG_PARPORT_NOT_PC is defined as this is needed to call the low level parallel port drivers. It is not otherwise used.
To build the Linux kernel do the following:
cd linux
make modules
When this has change back to the directory containing these sources and type:
make
You now have the 3 loadable kernel object files parport.ko and parport_sphat.ko
and lp.ko. These now need to be loaded (in that order) using the insmod command.