• HPS + FPGA

Tip

To control the FPGA LEDs, we need to know the addresses of the peripherals on the platform designer bus (AVALON). To avoid being dependent on magic numbers in our driver, we will use a PD tool that generates a .h file with the necessary information to control the peripherals.

In the project folder (hardware), execute:

$ embedded_command_shell.sh
$ sopc-create-header-files --single hps_0.h --module hps_0

This command will generate a file hps_0.h that contains the memory address information that we can use to access the peripherals on the FPGA:

/*
 * Macros for device 'led_pio', class 'altera_avalon_pio'
 * The macros are prefixed with 'LED_PIO_'.
 * The prefix is the slave descriptor.
 */
#define LED_PIO_COMPONENT_TYPE altera_avalon_pio
#define LED_PIO_COMPONENT_NAME led_pio
#define LED_PIO_BASE 0x3000
#define LED_PIO_SPAN 16
#define LED_PIO_END 0x300f
#define LED_PIO_BIT_CLEARING_EDGE_REGISTER 0
#define LED_PIO_BIT_MODIFYING_OUTPUT_REGISTER 0

Configuring the driver

We will work with the ebbchar example driver.

Exercise

Make a copy of the folde ebbchar to ebbchar-led.

Exercise

Copy the file hps_0.h into the driver folder.

We will need to edit the Makefile to support:

  1. Cross-compilation
  2. Quartus Embedded files and functions

Use the following file instead of the original Makefile:

# https://stackoverflow.com/questions/3467850/cross-compiling-a-kernel-module
ARCH=arm
COMPILER=arm-linux-gnueabihf-

ALT_DEVICE_FAMILY ?= soc_cv_av
SOCEDS_ROOT ?= $(SOCEDS_DEST_ROOT)
HWLIBS_ROOT = $(SOCEDS_ROOT)/ip/altera/hps/altera_hps/hwlib

#EXTRA_CFLAGS = -D$(ALT_DEVICE_FAMILY) -I$(HWLIBS_ROOT)/include/$(ALT_DEVICE_FAMILY) -I$(HWLIBS_ROOT)/include/

obj-m := ebbchar.o
KERNELDIR := /home/corsi/work/Embarcados-Avancados/Corsi/linux
PWD := $(shell pwd)

IP = 169.254.0.13
DEST = /root/driver/
PASS = 1234

all: ebbchar.ko, test

ebbchar.ko: ebbchar.c
    $(MAKE) -C $(KERNELDIR) M=$(PWD) ARCH=$(ARCH) CROSS_COMPILE=$(COMPILER) modules

test:
    $(COMPILER)gcc testebbchar.c -o test

deploy: ebbchar.ko test
    sshpass -p $(PASS) scp test root@$(IP):$(DEST)
    sshpass -p $(PASS) scp ebbchar.ko root@$(IP):$(DEST)

clean:
    $(MAKE) -C $(KERNELDIR) M=$(PWD) ARCH=$(ARCH) clean
    rm test

Exercise

  1. Edite the Makefile
  2. You should edit the variable KERNELDIR := to the path of the kernel you compiled.
  3. Edite the IP address

Understanding

In the Linux kernel, there are many functions available to manipulate hardware/physical memory addresses. We will only use the function: 

void iowrite32(u32 value, void __iomem *addr);

Info

This function writes a value to a physical memory address addr. To make this work, we must create a pointer that points to the PIO peripheral in the FPGA:

p_led = ioremap_nocache(ALT_LWFPGASLVS_OFST + LED_PIO_BASE, LED_PIO_SPAN);

Info

We are telling the kernel to create a pointer and that every access to this address must be enforced on the hardware, and cannot be cached.

Where p_led is a global and static variable of the module:

static int *p_led = NULL;

With this, we can now use the iowrite32 function and write to the LED PIO peripheral, we will make this writing inside the dev_write function, aiming to write the values passed by the write command to the LEDs.