4700 interrupts

We include a userspace IRQ patch in our kernels. This allows you to receive interrupts from your applications where you would normally have to write a kernel driver. This works by creating a file for each interrupt in '/proc/irq/<irqnum>/irq'. The new irq file allows you to block on a read on the file until an interrupt fires.

The original patch is documented here.

The Linux kernel on the TS-4700 supports up to 16 IRQs from the FPGA. When the CPU receives an IRQ from the FPGA, it uses the IRQ register in the #Syscon to find out which IRQ on the MUX is triggering. Currently only three IRQs are used. Off-board IRQs 5, 6, and 7 correspond to FPGA IRQs 0, 1, and 2, respectively. FPGA IRQs 3 to 15 are reserved for future uses. If the DIO pins are not being used as IRQs, they can be masked out by writing 0 to the corresponding bit in the IRQ mask register.

IRQ #	Name	Socket Location
49	Combined GPIO Interrupt	Any MFP pin
67	IRQ5/DIO_00	CN1-93
68	IRQ6/DIO_01	CN1-91
69	IRQ7/DIO_02	CN1-89

This example below will work with any of our TS-Socket boards running Linux. This opens the IRQ number specified in the first argument and prints when it detects an IRQ.

#include <stdio.h>
#include <fcntl.h>
#include <sys/select.h>
#include <sys/stat.h>
#include <unistd.h>

int main(int argc, char **argv)
{
	char proc_irq[32];
	int ret, irqfd = 0;
	int buf; // Holds irq junk data
	fd_set fds;

	if(argc < 2) {
		printf("Usage: %s <irq number>\n", argv[0]);
		return 1;
	}

	snprintf(proc_irq, sizeof(proc_irq), "/proc/irq/%d/irq", atoi(argv[1]));
	irqfd = open(proc_irq, O_RDONLY| O_NONBLOCK, S_IREAD);

	if(irqfd == -1) {
		printf("Could not open IRQ %s\n", argv[1]);
		return 1;
	}
	
	while(1) {
		FD_SET(irqfd, &fds); //add the fd to the set
		// See if the IRQ has any data available to read
		ret = select(irqfd + 1, &fds, NULL, NULL, NULL);
		
		if(FD_ISSET(irqfd, &fds))
		{
			FD_CLR(irqfd, &fds);  //Remove the filedes from set
			printf("IRQ detected\n");
			
			// Clear the junk data in the IRQ file
			read(irqfd, &buf, sizeof(buf));
		}
		
		//Sleep, or do any other processing here
		usleep(10000);
	}
	
	return 0;
}

Any of the MFP pins can be repurposed to trigger IRQ 49. For example, to make MFP_46 (CN2_72) trigger on a rising edge:

# Enable rising edge detection on MFP_46
peekpoke 32 0xD4019034 0x4000

# Unmask MFP_46
peekpoke 32 0xD40190A0 0x4000

# to clear the interrupt after it has been triggered
peekpoke 32 0xD401904c 0x4000

The IRQ numbers 67-69 are muxed IRQs which are only enabled when using the #MUXBUS. You can enable these by running these commands:

# If you're in Debian you need this next line
# source /initrd/ts4700.subr
pc104on

This will repurpose other DIO for the #MUXBUS data, address, and bus control lines as well.

See page 169 of the CPU manual for more information on the interrupt controller.