Fetching the latest value from external sources using Channel

General Usage
1

Hi!

Sorry for my bad English to describe the title.

I am trying to make a small code which fetches a value from a MCU (Arduino, ESP32, etc.) upon request.

The MCU periodically saves the sensor value measured into its variable, and it sends the value of the variable to Julia upon receving a predefined serial message.

On the Julia side, I decided to use Channel to fetch the value.

using LibSerialPort

sp = LibSerialPort.open("COM4", 115200)

chnl = Channel()

function getsensorval(c::Channel, p::SerialPort)
    while true
        write(sp, "1\n")
        sleep(0.01)
        if bytesavailable(p) > 0
            t = String(read(p))
            t = split(t)[end]
            put!(c, t)
        end
    end
end

One problem is that the loop in getsensorval helds before put! until task!(chnl) is executed, and the value stored in t remains old. As a result, I only could get an old value of t when executing task!(chnl) after a long period. This makes me run task! again to update the latest value.

One WE mimicking this problem without MCUs is:

x = 0

function genval()    # increases x by 1 a second
    while true
        global x += 1        
        sleep(1)
    end
end

function readval(c::Channel)
    while true
        t = string(x)
        put!(c, t)
    end
end

chnl = Channel()
@async genval()
@async readval(chnl)

julia> take!(chnl) # executed immediately
"1"   

julia> take!(chnl) # executed again after about one minute from the first take! (expecting "50"~"70")
"1"   

julia> take!(chnl) # executed immediately after the second execution
"53"

Is there a way to solve the issue?
Always appreciate comments from the community.