BaremetalPi on Raspberry PI 5

[JakeZw]

This discussion pertains to the Raspberry PI OS both up to date using the 64 bit version.

In the init_gpio() function in the file gpio.jl the device /dev/gpiomem is hardcoded into BaremetalPi.

While this works well on my RPI 4, the RPI 5 does not have this device. Rather it has '/dev/gpiomem0-dev/gpiomem4each with a different major number. The major number for RPI 4/dev/gpiomemis 237. On the RPI 5 the device with this major number is/dev/gpiomem2`. I assume this is important.

I modified a local copy of BaremetalPi with this change and then init_gpio() no longer errors.

What BaremetalPi now needs is a way to determine whether to use '/dev/gpiomemor/dev/gpiomem2`. This could be done by one of the following:

• determine if the Pi is 4 or 5
• search the /dev folder to see which one exists
• search the /dev folder to see which character device has major number 237

Not known
Whether this works with other OS's

If you have a preferred implementation I can test it.

[JakeZw]

The above is one problem, there are more. I use a simple function I call trigger to create a short duration pulse on a pin, in my case gpio pin 23. the function is:

function trigger(pin::Int; duration::Real = 0.050) init_gpio() gpio_set_mode(pin, :out) try gpio_set(pin) sleep(duration) gpio_clear(pin) finally gpio_set_mode(pin, :in) end end

If I execute this code a line at a time, it hangs the RPI 5 on the command gpio_set(pin). The output of pin 23 does not change. I will try and get more details.

[JakeZw]

Slowly getting more information. the function `init_gpio() now looks like this:

`
"""
init_gpio()

Initialize the GPIO.
"""
function init_gpio()
# Open and map /dev/gpiomem or on RPI 5 /dev/gpiomem2
try
files = readdir("/dev")
if sum(files .== "gpiomem") == 1
gpiomem = "/dev/gpiomem"
elseif sum(files .== "gpiomem2") == 1
gpiomem = "/dev/gpiomem2"
end
gpiomem_io = open(gpiomem, "w+")
gpiomem_map = Mmap.mmap(
gpiomem_io,
Vector{UInt32},
(GPIOMEM_SIZE,),
0,
grow = false
)

    objects.gpiomem_io  = gpiomem_io
    objects.gpiomem_map = gpiomem_map
    objects.gpio_init   = true
catch
    error("Could not map `/dev/gpiomem` or `/dev/gpiomem2`. Make sure you have the required permissions.")
end

return nothing

end
`

The if-then-else will point to a device that accounts for the Raspberry PI 5 difference. I was guessing that /dev/gpiomem2 would be the correct device based on the major number but usuing this in Mmap.mmap function makes the computer unresponsive a total hang which requires a power off power on cycle. According to this site https://wiki.gentoo.org/wiki/Raspberry_Pi_Install_Guide/Raspberry_Pi_GPIO I should be using /dev/gpiochip4 but this gives me a permission denied error. It does indicate that the Raspberry PI 5 is different from the PI 4.

According to https://forums.raspberrypi.com/viewtopic.php?t=357679 90% of users should be using /dev/gpiomem0.

I am not sure if I can go much further on this.

[JakeZw]

Possibly useful resources:

https://www.i-programmer.info/programming/148-hardware/16887-raspberry-pi-iot-in-c-pi-5-memory-mapped-gpio.html

https://www.i-programmer.info/programming/148-hardware/17867-raspberry-pi-5-iot-in-c-gpio-registers.html

It looks like /dev/gpiomem0 should be used, contrary to my initial guess.