DA14580 Bootloader not completing

Hi,

I am trying to use the DA14580 factory delivered bootloader to load in my code (a slightly modified DSPS central), and I "almost" succeed...

Using the DA14580_CB_PXI_QFN48 module on a Development Kit Expert, I have tested that the Keil Project and its generated hex file works
预期的效果。

I am now powering up an unprogrammed DA14580 (the setup from above), connecting a UART to GPIOA.4 and GPIOA.5 and communicate
with the DA14580 during its bootloading sequence. Following the application note AN-B-001, I can see the STX = 0x02 on the UART,
and I reply with SOH = 0x01, LEN_LSB = 0x00, LEN_MSB = 0x40. I then get ACK = 0x06 and I start shooting code bytes to the DA14580.

However, I do not get a consistent CRC back, and if I give the last ACK = 0x06 nothing happens

Actually, looking at the UART pins with an oscilloscope reveals that the GPIOA.4, DA14580 UART TX is being released and becomes floating
在某个地方the code bytes transmission.

One thing I am a bit unsure of is the hex file conversion into code bytes. I have written a C# program that converts the sps_host.hex
into a C header file with a const uint8_t thecode[16000] array. The one thing I was not sure how to handle was that in the hex file there
are some gaps; ie the intel hex file format specifies the start address for each line of 16 code bytes. But my sps_host.hex file has 4 regions of code, with 3
chunks of empty space of various length between them. Using SmartSnippets Toolbox's OTP Image tool, I load the sps_host.hex file and can see how the
empty spaces are represented by "--" symbols in the Hex field. In my conversion program I simply filled these bytes with "0" (zeroes).
Also, the sps_host.hex file contains 15360 bytes, whereas my program pads with zeroes up to a total length of 16000 bytes.

I feel very stuck, and would appreciate some hint what direction to run?

BR
Roger