RE: DTM test w/ nAN34 examply.py

Hsu — Wed, 03 Jul 2019 09:55:42 GMT

Hi Bjørn,

It's clear.

Thank you.

RE: DTM test w/ nAN34 examply.py

bjorn-spockeli — Tue, 02 Jul 2019 09:45:50 GMT

Hi Hanyu,

the an empty DTM test packet is 10 bytes, so adding a payload length of 10 will result in a total packet length of 20bytes. When using the 1Mbit Radio mode, the radio will use 8uS per byte, so 20byte * 8uS/byte = 160uS. However, when using the 250kbit mode, the transmission time per byte is increased by a factor of 4, i.e. 32uS per byte, so the same 20byte packet will now take 32uS/byte*20byte = 640uS to transmit.

If we look at the DTM code from SDK 12.3.0, we can see that the code assumes that 1Mbit is used as it uses the 8uS/byte factor to calculate the transmission time of a packet of a given m_packet_length.

 // Set the timer to the correct period. The delay between each packet is described in the
        // Bluetooth Core Spsification version 4.2 Vol. 6 Part F Section 4.1.6.
        if ((m_packet_length + DTM_ON_AIR_OVERHEAD_SIZE ) * 8  <= 376)
        {
            mp_timer->CC[0]       = 625;                        // 625uS with 1MHz clock to the timer
        }
        else if ((m_packet_length + DTM_ON_AIR_OVERHEAD_SIZE ) * 8  <= 1000)
        {
            mp_timer->CC[0]       = 1250;                        // 625uS with 1MHz clock to the timer
        }
        else if ((m_packet_length + DTM_ON_AIR_OVERHEAD_SIZE ) * 8  <= 1624)
        {
            mp_timer->CC[0]       = 1875;                        // 625uS with 1MHz clock to the timer
        }
        else
        {
            mp_timer->CC[0]       = 2500;                        // 625uS with 1MHz clock to the timer
        }

        // Configure PPI so that timer will activate radio every 625 us
        NRF_PPI->CH[0].EEP = (uint32_t)&mp_timer->EVENTS_COMPARE[0];
        NRF_PPI->CH[0].TEP = (uint32_t)&NRF_RADIO->TASKS_TXEN;
        NRF_PPI->CHENSET   = 0x01;
        m_state            = STATE_TRANSMITTER_TEST;

In our case the DTM code will send a packet every 625uS as the total packet length is 20byte, but each packet will take 640uS when using the 250kbit mode.

In the python code it also assumes that a packet will maximum use 625uS per packet.

	def _calculateTimeForPackage (self):
		"""Calculate how long time from start of one package to the start of next"""
		return 0.625*2

So I think if you modify the DTM code(dtm_cmd() in ble_dtm.c) as shown below to take in to account for the 4 time increase in transmit time.

 if ((m_packet_length + DTM_ON_AIR_OVERHEAD_SIZE ) * 32  <= 376)
        {
            mp_timer->CC[0]       = 625;                        // 625uS with 1MHz clock to the timer
        }
        else if ((m_packet_length + DTM_ON_AIR_OVERHEAD_SIZE ) * 32  <= 1000)
        {
            mp_timer->CC[0]       = 1250;                        // 625uS with 1MHz clock to the timer
        }
        else if ((m_packet_length + DTM_ON_AIR_OVERHEAD_SIZE ) * 32  <= 1624)
        {
            mp_timer->CC[0]       = 1875;                        // 625uS with 1MHz clock to the timer
        }
        else
        {
            mp_timer->CC[0]       = 2500;                        // 625uS with 1MHz clock to the timer
        }

and multiply the total time from one packet to the next in the python script by 2

	def _calculateTimeForPackage (self):
		"""Calculate how long time from start of one package to the start of next"""
		return 0.625*2

then I think you should get better results with the payload length set to 10 in the python script.

Best regards

Bjørn

RE: DTM test w/ nAN34 examply.py

Hsu — Tue, 02 Jul 2019 02:48:41 GMT

Hi Bjørn,

It improves the PER, thanks for your help.

Based on the original setting, the 10 bytes should not long.

I think it should work at 250K/1M/2M link speed.

Could you share why reduce the length/runtime can improve the PER?

Thank you.

BRs, Han

RE: DTM test w/ nAN34 examply.py

bjorn-spockeli — Mon, 01 Jul 2019 12:17:05 GMT

HI Hanyu,

can you reduce the test packet length to 5 and the runtime to 50, i.e.

setup['Length'] = 5 #Length of the test package

setup['Runtime'] = 50 #How long the Receiver should be receiving. In ms

and see if that improves the PER?

Best regards

Bjørn