driver-74hc595

A linux kernel driver for the 74HC595

Usage

1. Compile with make
2. Insert the kernel module into the kernel using insmod driver.ko <parameters>
3. Read / Write to /dev/chip74hc595

Module parameters

Name	Description	Range	Default value
clock_pin	Sets the clock pin	uint8_t	3
data_pin	Sets the data pin	uint8_t	0
latch_pin	Sets the latch pin	uint8_t	1
reset_pin	Sets the reset pin, if the pin < 0 then its ignored	int16_t	-1
chain_len	Sets the amount of shift registers chained together	uint8_t	1
delay	Sets the clock's delay (in nanoseconds)	uint64_t	50
device_name	Sets the device name, alphanumeric, 2-20 chars	char*	chip74hc595

IOCTL syscall commands

Name	Description	Command (ioctl_595.h)	Arguments
Reset	Resets the register chain	IOCTL_RESET_595	void
Read chain length	Reads the chain length	IOCTL_READ_CHAIN_LENGTH	uint8_t*
Latch	Manually latches the 595	IOCTL_MANUAL_LATCH	void
Automatic latch	Enables/Disables automatic latching	IOCTL_SET_AUTO_LATCH	bool

Tested configurations

Hardware	Kernel	Dstribution	Status
OrangePi Zero	3.4.113	Armbian Xenial	Well Supported
OrangePi Zero	4.14	Armbian Bionic	Well Supported
Raspberry Pi 2	4.14	Raspbian Stretch	Well Supported
Raspberry Pi 3B+	4.19.57	Raspbian Stretch	Well Supported
BananaPi M2 Zero	5.15.69	Armbian Buster	Well Supported
BananaPi M2 Zero	6.12.58	Buildroot	Well Supported
Generic boards	3.X	Any	Supported, Needs testing
Generic boards	4.X	Any	Well Supported
Generic boards	5.X	Any	Supported, Needs testing
Generic boards	>5.2	Any	Supported, Untested
Generic boards	<3.0	Any	Unsupported

Known Issues and concerns

• Dosen't work with fwrite (even though they use the same base system call)
  • Caused by fwrite's buffering when it's not supposed to
  • Buffering is easily disabled by using setbuf(fp, NULL);, this fixes the problem
• No support for output enable pin, this should be tied to ground or another GPIO
• Please report any issues to the issues section!