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stawel
IMAX B6 (original): Wrong UART bitrates at high speeds (38400++)
I'm have flashed original IMAX B6 with stawel/cheali-charger@fe5e5c0a and have issues with PC connection. It works fine on 9600 and 19200, but on 38400++ only garbage is recieved. I have logic analyzer device and so decided to measure real UART bitrates on adapter and IMAX, and found werid thing: Adapter bitrates (nominal vs real): 9600: 9933 19200: 19277 38400: 39538 57600: 57692 115200: 115384
IMAX bitrates (nominal vs real, Autoband feature is enabled on logic analyzer): 9600: 9884 (works with adapter) 19200: 20304 (works with adapter) 38400: 43087 (garbage only with adapter, framing errors with analyzer) 57600: 70381 (garbage only with adapter, framing errors with analyzer) 115200: 175182 (garbage only with adapter, framing errors with analyzer) But when I tried to disable Autoband feature on logic analyzer and manually set correct bitrate for protocol decoding - analyzer decoded data correctly. But UART adapter still doesn't work with IMAX on those speeds. Here is Saleae Logic saved data:
IMAX_B6_UART_115200.zip Is there something bad with mine IMAX? I had tried to use another adapter, but it doesn't worked at all (no garbage even).
Hi @S-trace, Your charger crystal oscillator seems to be oscillating on different frequency. it has 112% baud rate on 38400. That is too much. (never seen it) You can measure frequency on crystal if you have oscilloscope. There should be 16MHz.
I can't calculate it's frequency from prescaler formula. Did your measurements matched repeatedly?
Can you upload zip somewhere else? Github reports error when I try to download it.
Can you capture several frames with higher sample rate? 16MHz or more if possible.
IMAX_B6_UART_115200_v2.logicdata.zip 115200: 175182 with autobaud. But stream decoded fine on 115200 fixed baudrate
Still 2.4MHz sample rate. Shortest pulse seems to be around 5.8us, It should be around 8.7us fo 115200. That is strange. Can you check value printed on crystal?
Also you need your uart to be set to 8 data bits, no parity, 1 stop bit. No sure what do sou use for data receiving.
Hello, @diggit No, i did not solved it. The oscillator in mine IMAX have 16.000 printed on its cover, but i'm have no oscilloscope to measure real frequency. I'm always using 8n1 options for UART adapter with IMAX, bitrate is only variable value.
You can try to slightly increase F_CPU in avr-compiler.cmake and build new FW with this value changed.
if you are using a CP2102 based UART dongle you could also try to remove a 1kOhm resistor: https://groups.google.com/forum/#!searchin/cheali-charger/uart|sort:relevance/cheali-charger/LKy6qITaVDg/FvYe_ZY7C9EJ
