USB Secure DFU speed

[Anantha Keshava]

I'm using USB based DFU on Windows and on Linux 18.04 LTS VM on Windows.

Platform: nRF52840-Preview-DK

SDK version: 15.0.0 (nRF5_SDK_15.0.0_a53641a)

example USB Secure DFU. Here are the steps I perform:

1. Erase the Flash: $ nrfjprog -f NRF52 --recover
2. Flash the softdevice ver 6.0.0: $ nrfjprog -f NRF52 --program ~/workspace/src/SDK/components/softdevice/s140/hex/s140_nrf52_6.0.0_softdevice.hex --sectorerase
3. Flash the Bootloader settings: $ nrfjprog -f NRF52 --program ~/workspace/src/SDK/examples/dfu/secure_bootloader/pca10056_usb/armgcc/bl_settings.hex --sectorerase
4. Flash the Bootloader: $ nrfjprog -f nrf52 --program ~/workspace/src/SDK/examples/dfu/secure_bootloader/pca10056_usb/armgcc/_build/nrf52840_xxaa.hex --sectoranduicrerase --reset

Perform DFU (Device is in bootloader mode at this point as LED 1 and LED 3 are lit up).

1. $ time sudo nrfutil dfu usb_serial -pkg _build/ble_app_freertos_gcc_nrf52.zip -p /dev/ttyACM1 -b 115200 -fc 1

OR

1. $ nrfutil dfu usb_serial -pkg "C:\Data\workspace\expt\ble_app_freertos_gcc_nrf52.zip" -p COM6 -b 1000000 -fc 1

I have two issues:

1. On linux, only 115K BAUD seems to work and higher bauds even with HWFC gives error or the DFU hangs infinitely at 0%.
2. In both cases the time taken to update is about same giving me a throughput in the range 118kbps to 130kbps which seems awfully slow for USB FS at 12Mbps.

I originally tried UART DFU but couldn't get it to work higher than 250000 BAUD

Is there anyway I can achieve higher speeds for DFU?

[Kenneth]

The main limitation here is likely the flash erase, write and verify operation, the CPU is halted during these operations, thereby 115200 is the max baud you should use.

[Anantha Keshava]

Hi Kenneth, Thanks for your response.

Are there any known numbers for these operations in terms of duration for performing a page of erase, write, verify etc? This will be extremely helpful in evaluation of platforms and manufacturing plans.

[bjorn-spockeli]

HI Anantha, 

I apologize for the late reply. As my colleague Kenneth has written, the low throughput is related to the DFU protocol and flash write/erase times, not the USB peripheral. I will see if I can dig up some performance numbers for our serial bootloader. The flash write/erase duration can be found in the NVMC's  Electrical specification  section.

Bjørn 

[Anantha Keshava]

Thanks bjorn-spockeli.

Are there any protocol level delays for subsequent commands/data sent to the BL during DFU? Are there any steps to follow to reduce the time to perform DFU on a given medium of transfer?

[bjorn-spockeli]

Hi Anantha, 

I discussed this with the developers that developed the SDK v15.0.0 bootloaders and according to them we've spent significant efforts on optimizing the SDK v15.0.0 bootloaders in terms of throughput, both with the BLE and serial transport layers. Hence, there are not that many knobs left to tinker with to increase the throughput with the current bootloader design. 

Best regards

Bjørn