We are experiencing bizarre, bizarre DFU problems.
I have a custom circuit board with a NRF51822-QFAC - when I initiate a DFU with an iPod touch purchased in the United Kingdom, the update succeeds. When I initiate a DFU with an iPod touch purchased in the United States it fails.
Specifically I am initiating a DFU update from the United States through the Noridc NRF Toolbox 2.4 on an iPod touch running iOS 8 and using SDK 9.0 our upload times out after 4 packets (0%) and says "DFU The connection has been lost". When doing the same thing from a device in the United Kingdom the process completes successfully.
We have mailed a second US based iPod Touch to the UK - the developer in the UK experiences DFU failure when using the American device to initiate updates. Sending a second UK based iPod touch device to the US results in DFU success when using the UK iPod touch.
Both iPod touches are using the latest NRF Toolbox app (nRF Toolbox Version 2.4) and latest version of iOS 8.4.1 - (have not upgraded to iOS 9 yet). We can replicate the behavior using iPhone 6 devices as well as Galaxy S4's. (US versions of the three products fail, UK versions succeed).
We have confirmed this behavior across 10 different NRF51822-QFAC (5 in the US, 5 in the UK) - all 5 fail when taking a DFU from a US based iPhone 6 or iPod Touch. All 5 succeed when taking an update from a UK device. Sending failed boards to the UK results in success. US start working in the UK and vice versa.
The firmware on the device is identical. Dumping the firmware using a Segger script and doing a hex compare confirms this. The boards are identical. The only variation we can track down is the device locale type.
Why would the US version of nRF Toolbox 2.4 fail, while the UK version of nRF Toolbox 2.4 works?
As best as we can deduce, calls to hci_mem_pool_rx_extract succeed when coming from UK phones but not US ones. Is UK bluetooth somehow slower or faster? (As insane as that sounds). It follows that this buffer fills up when initiating an update from a US phone but is being cleared in time for UK phones. I know the WiFi spec has variation by location but was not under the impression BLE did.
The issues we are seeing are very similar as the ones described in this thread: devzone.nordicsemi.com/.../ - the solution there of increasing queue size did not solve our problem.
We only encountered this issue when upgrading from SDK 7 to SDK 9. All DFU functionally was previously working both on US and UK phones with SDK 7.
