Power on sequence, modem off

[Will Blight]

I am working on a low current (battery powered) application. Power to the dragonfly is removed most of the time. When power is applied I do not want the modem to power up immediately it uses to much current. I need the M4 to work for a period of time and then power on the modem and send the data.
I created the code below by combining the HTTP example, Flash example and the low power example code on mbed.
If I used the HTTP example code the dragonfly powers up, connects to the website and post data in about 15 to 20 seconds. If I use the code below to keep the modem powered down after power has been applied, sometimes (not always) when I power up the modem in code it takes minutes (if ever) to connect to the server and post the data.

My question is: what is the correct sequence of events to power off the modem when power is first applied and to power it back on at a later time?

Thanks.

My code looks like this: (it was nicely formatted before I hit the submit button.)
Int main()
{
//keep modem powered off.
radio_pwr = 0;
radio_reset = 0;

bc_nce = 1;
wait_ms(100);

Process_this();
Process_that();

log(“changing regulator to 1A mode \n”);
bc_en1 = 0;
bc_en2 = 1;
log(“waking up the SPI flash \n”);
//flash code not shown.
flash.wakeup();
read_values_from_flash();

wait_ms(100);

radio_reset = 1;
wait_ms(100);

log(“powering on radio \n”);
radio_pwr = 1;
radio_reset = 1;
int tries = 0;

log(“radio_ok = init_mtsas() \n”);
radio_ok = init_mtsas();
if (! radio_ok) {
log(“failed to initialize cellular radio \n”);
shutdown();
}

while (radio->sendBasicCommand(“AT”, 1000) != MTS_SUCCESS) {
//wait(1);
wait_ms(200);
tries++;
if (tries % 100 == 0) {
radio_reset = 0;
wait_ms(10);
radio_reset = 1;
}
log(“.”);
}
log(“\n”);

log(“setting APN \n”);
if (radio->setApn(apn) != MTS_SUCCESS) {
shutdown();
}

log(“bringing up the link \n”);
if (! radio->connect()) {
log(“failed to bring up the link \n”);
shutdown();
} else {
// do HTTP stuff here
}

shutdown();
}
return 0;
}

[Mike Fiore]

Will,

The Dragonfly low power example program you mentioned

https://developer.mbed.org/teams/MultiTech/code/Dragonfly_Low_Power_Example/

demonstrates how to properly shut down and turn on the radio.

You should raise the radio_pwr line before raising the radio_reset line. Raising these lines in the opposite order as your application is currently doing could be the cause of your delays, I think.

That is what I noticed right away, but since I don’t have your entire application, I can’t know for sure if there are any other issues.

Cheers,

Mike

[Will Blight]

Hi Mike,
The rest of the code is from the examples. The HTML section is directly from the HTML example with the a slight change to use “GET” to post data.
The shutdown() function is the code from the low power example. I am basically waiting for the modem to shutdown so I can remove power from the board safely.

I have thoroughly tested the application code. I use functions outside of the main loop to perform the work I need done. Using printf() with the development kit and my oscilloscope monitoring output pins I can see that my functions complete correctly. The problem is in the modem section.

I will remove the radio_reset from before the radio_pwr.

I see in the while loop code:
“while (radio->sendBasicCommand(“AT”, 1000) != MTS_SUCCESS)”

that radio_reset is toggled off and on with a 10ms delay between. Is there a delay required between setting radio_pwr and setting radio_reset?

Will.

[Mike Fiore]

Will,

No delay is required between raising radio power and radio reset. The radio_pwr line just has to be raised first.

Cheers,

-Mike

[Author]

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