patacongo edited a comment on issue #3665:
URL: 
https://github.com/apache/incubator-nuttx/issues/3665#issuecomment-833531356


   > t drops chars with HW flow control (on chip).
   
   Isn't that due to the lack of RX/TX FIFOs on the serial peripheral?  That 
causes this bad behavior if the chip hardware flow control is enabled:  
https://github.com/apache/incubator-nuttx/blob/master/arch/arm/src/stm32/Kconfig#L9409
 and 
https://github.com/apache/incubator-nuttx/blob/master/arch/arm/src/stm32l4/Kconfig#L5656
 (I guess you should know all about that since you added the FLOWCONTROL_BROLEN 
kludge).
   
    The H7 (and maybe others) do have FIFOs and should not required the 
FLOWCONTROL_BROKEN kludge.
   
   That little circular RX DMA was added by Mike Smith to account for data 
losses because of the lack of Rx FIFOs on the STM32 F4 family.  It should not 
be necessary if the U[S]ART peripheral has hardware FIFOs.  The original H7 did 
not support this circular DMA (as I recall) because it was not needed.
   
   -


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