nRF5 action!

[mfalkvidd]

@NeverDie not sure if you've already noticed, but 4294967295 is the maximum value for an unsigned 32-bit integer. So the value is 0xFFFFFFFF. That often means uninitialized. I don't know why it would be uninitialized though.

[NeverDie]

@mfalkvidd

Maybe because they just never were?
Those particular registers are "The user information configuration registers (UICRs) are non-volatile memory (NVM) registers for configuring user specific settings." So, it would seem that initializing them just once would be enough, since they're non-volatile.

In any case, good catch! It explains both why they are that value and also why they match.

[NeverDie]

@NeverDie said in nRF5 Bluetooth action!:

4294967295

Also, since 4294967295 equals 0xFFFFFFFF, then bit 31 is a '1', which, according to the datasheet, means the pin is disconnected (see section 14.1.60 PSELRESET[0] of the datasheet for the detail].

[NeverDie]

@mfalkvidd said in nRF5 Bluetooth action!:

So the value is 0xFFFFFFFF. That often means uninitialized. I don't know why it would be uninitialized though.

There's a chance we may have unwittingly done it ourselves! Remember back to when we were doing an explicit "Erase All"? From the datasheet:

11.5 Erase all
When erase is enabled, the whole Flash and UICR can be erased in one operation by using the ERASEALL
register.

Furthermore, from page 29 of the datasheet:

After erasing UICR all bits in UICR are set to '1'.

[d00616]

@NeverDie said in nRF5 Bluetooth action!:

@mfalkvidd said in nRF5 Bluetooth action!:

So the value is 0xFFFFFFFF. That often means uninitialized. I don't know why it would be uninitialized though.

There's a chance we may have unwittingly done it ourselves! Remember back to when we were doing an explicit "Erase All"? From the datasheet:

This is part of the arduino-nrf5 code -> https://github.com/sandeepmistry/arduino-nRF5/blob/dc53980c8bac27898fca90d8ecb268e11111edc1/cores/nRF5/SDK/components/toolchain/system_nrf52.c#L156

I don't have any idea why this is not included in the binary. When the reset menu is selected then "-DCONFIG_GPIO_AS_PINRESET" is given to gcc.

When system_nrf52.c is completely ignored, then the erratas are not handled.

[NeverDie]

Here is some verbose code which properly sets the registers to use pin P0.21 as the RESET pin:

Serial.println("Testing...");
delay(10000);  //give preparation time to open serial tty
Serial.print(counter);
Serial.print(", PSELRESET[0]=");
Serial.println(NRF_UICR-> PSELRESET[0]);
Serial.print(counter++);
Serial.print(", PSELRESET[1]=");
Serial.println(NRF_UICR-> PSELRESET[1]);

Serial.println();
Serial.println("Write-enabling CONFIG.");
NRF_NVMC->CONFIG=1;  // Write enable the UICR

Serial.println();
Serial.println("Now designating pin pO.21 as the RESET pin.");
NRF_UICR-> PSELRESET[0]=21;  //designate pin pO.21 as the RESET pin
NRF_UICR-> PSELRESET[1]=21;  //designate pin pO.21 as the RESET pin

Serial.println();
Serial.println("Confirming that RESET pin assigment took hold:");
Serial.print(counter);
Serial.print(", PSELRESET[0]=");
Serial.println(NRF_UICR-> PSELRESET[0]);
Serial.print(counter++);
Serial.print(", PSELRESET[1]=");
Serial.println(NRF_UICR-> PSELRESET[1]);

Serial.println();
Serial.println("Return CONFIG to read-only mode.");
NRF_NVMC->CONFIG=0;  // Put the UICR back into read-only mode.

Running it once seems to be good enough, unless there were to occur another "Erase All" or "Burn bootloader" event.

Here is the output from running the code which shows that it succeeded:

Testing...
0, PSELRESET[0]=4294967295
0, PSELRESET[1]=4294967295

Write-enabling CONFIG.

Now designating pin pO.21 as the RESET pin.

Confirming that RESET pin assigment took hold:
1, PSELRESET[0]=21
1, PSELRESET[1]=21

Return CONFIG to read-only mode.

[NeverDie]

Until a more elegant solution can be found, I'm using this in the setup() routine as the workaround:

  if (((NRF_UICR-> PSELRESET[0])==0xFFFFFFFF) && ((NRF_UICR-> PSELRESET[1])==0xFFFFFFFF)) { //if the two RESET registers are erased
    NRF_NVMC->CONFIG=1;  // Write enable the UICR
    NRF_UICR-> PSELRESET[0]=21;  //designate pin P0.21 as the RESET pin
    NRF_UICR-> PSELRESET[1]=21;  //designate pin P0.21 as the RESET pin
    NRF_NVMC->CONFIG=0;  // Put the UICR back into read-only mode.
  }

The code has the positive virtue of not writing to the RESET rregisters unless both registers are erased. That helps ensure that the non-volatile memory does not get worn out prematurely.

[NeverDie]

@NeverDie said in nRF5 Bluetooth action!:

Until a more elegant solution can be found, I'm using this in the setup() routine as the workaround:

  if (((NRF_UICR-> PSELRESET[0])==0xFFFFFFFF) && ((NRF_UICR-> PSELRESET[1])==0xFFFFFFFF)) { //if the two RESET registers are erased
    NRF_NVMC->CONFIG=1;  // Write enable the UICR
    NRF_UICR-> PSELRESET[0]=21;  //designate pin P0.21 as the RESET pin
    NRF_UICR-> PSELRESET[1]=21;  //designate pin P0.21 as the RESET pin
    NRF_NVMC->CONFIG=0;  // Put the UICR back into read-only mode.
  }

The code has the positive virtue of not writing to the RESET rregisters unless both registers are erased. That helps ensure that the non-volatile memory does not get worn out prematurely.

Good news! I've confirmed that doing this does indeed solve the problem I previously had with the EByte nRF52832 module not reacting to a reset on pin P0.21. After inserting the above code block into the nRF52832's setup() routine, I can now, using ESP-LINK, remotely reset an nRF52832 module:
https://www.openhardware.io/view/443/nRF52832-ESP-LINK-Shield-for-ESP8266-Wemos-D1-Mini

[NeverDie]

With that issue now settled, I'm moving on to a different topic: what happens if you put the radio into Tx mode, but with an empty buffer (i.e. nothing to send)? In this scenario an RFM69 transmits a continuous pre-amble, and I'm wondering whether the nRF52832 does the same?
With an empty buffer, does it transmit anything at all? Anyone happen to know?

The reason I ask is that I want to program the radio to send a continuous signal so as to quickly wake-up a receiver. With packets, there's the lag time of receiving and decoding the packet, rather than just reacting to a high RSSI. In this way, I can use much narrower listen windows and thereby save a lot of current consumption.

[NeverDie]

According to the datasheet, the typical RSSI sample period is just 0.25us. However, what spoils that a bit is that the radio has to come up to speed beforehand.

Anyhow, on the receive side, I now have at least that much working.

[NeverDie]

It looks as though the start-up time for the radio is about 390us. So, it does save a lot of current to first check the RSSI level rather than to always listen for a packet.

[NeverDie]

When I measure RSSI on the nRF52832, I get what seems like a rather odd range of values: between about 94 and 127. If I have no other nodes transmitting, then the RSSI is generally around 100. If I set up another node which deliberately transmits on the same channel, then the RSSI is pegged at 127.

Is that what others here are also seeing? Here's the test code:

uint8_t theRSSI;
void loop() {
  
NRF_RADIO->TASKS_RXEN=1;  //start revving up the receiver
while (!(NRF_RADIO->EVENTS_READY)) {} //busy-wait until radio ready to receive
NRF_RADIO->TASKS_RSSISTART=1;  //Take exactly one RSSI sample
while (!(NRF_RADIO->EVENTS_RSSIEND)) {}  //Busy-wait until RSSI sample is completed.
theRSSI = NRF_RADIO->RSSISAMPLE;

Serial.println(theRSSI);
Serial.flush();
sleep(1000);
}

[NeverDie]

Unfortunately, when I use the above code block and test the current using an oscilliscope, it becomes clear that the radio never actually goes to sleep:

So, to do that, I add the line:

NRF_RADIO->TASKS_DISABLE=1;  //turn-off the radio

just prior to sleep(100). Doing that largely eliminates the current drain while sleeping:

However, if I do that, then the RSSI that gets reported is always 127. Why? Do I need some other way to check the radio states? Maybe STATE from section 23.14.25 STATE of the datasheet would work better?

[NeverDie]

Found a breakout board for the nRF51822-04: https://oshpark.com/shared_projects/zqDQaykJ

[NeverDie]

The datasheet is possibly a bit misleading when it says:

For the RSSI sample to be valid the radio has to be enabled in receive mode (RXEN task) and the reception
has to be started (READY event followed by START task).

I'm finding that the radio needs to be in either RXIDLE state or RX state to get a plausible RSSI measurement. I can't get a reasonable RSSI measurement while within the RXRU state.

[d00616]

@NeverDie said in nRF5 Bluetooth action!:

The datasheet is possibly a bit misleading when it says:

For the RSSI sample to be valid the radio has to be enabled in receive mode (RXEN task) and the reception
has to be started (READY event followed by START task).

I'm finding that the radio needs to be in either RXIDLE state or RX state to get a plausible RSSI measurement. I can't get a reasonable RSSI measurement while within the RXEN state.

In the ESB code, I use the bitcounter event to start the rssi sample task via PPI. The results are looking plausible.

[NeverDie]

I've found that I get a slightly stronger RSSI signal by about 3dB if I measure it while in the RX state rather than the RXIDLE state.

[NeverDie]

@d00616 said in nRF5 Bluetooth action!:

In the ESB code, I use the bitcounter event to start the rssi sample task via PPI. The results are looking plausible.

Do you know of any good PPI tutorials? The datasheet seems awfully skimpy on its explanation of exactly how to use it.

Right now I have RSSI triggers working on the receiver (presently using the MCU, not PPI), but it takes 1400 samples to guarantee not missing any transmissions. That's because of the gap between single shot packets when they get sent. If I can reduce that to one sample, by finding a way to make a transmitter transmit continuously, then that will save a lot of energy on the receiver.

There is a way to do more rapid fire transmission of packets, so that would be the fall-back plan if I can't find a way to, for example, send a continuous preamble.

[NeverDie]

Answering my own question: it turns out that if you enter into TX mode without any payload, it just sends a null packet and returns to TXIDLE. So, it is not like the RFM69, which would simply send an indefinitely long preamble until there's a payload to send.

The goal is to close the gap between packets as much as possible. So, I'm getting some improvement by just immediately switching back into TX mode (to send another null packet) the moment I've confirmed that TXIDLE state has re-occured.

[NeverDie]

As it turns out, using the above method packs the null packets so tightly that I can rely on a single RSSI measurement (instead of 1400 of them) to guarantee that a transmission won't be missed. So, the goal is achieved.

It sounds as though combining PPI with this would drive the energy consumption even lower! :)