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AHorn.0
AHorn.0
Visitor II
October 30, 2019
Question

STM32L0x2: Combine two comparator outputs

  • October 30, 2019
  • 1 reply
  • 1325 views

I have a STM32L072KB microcontroller and want to combine two analog signals (they represent a kind of "quadrature encoded signal" with a 50% duty cycle) into one "combined digital output signal", which have the doubled frequency (for my purpose the doubled output signal is used to provide the doubled accuracy)

0690X00000ArSL8QAN.pngI am using the both comparator peripherals COMP1 and COMP2 for detecting the signal edges and it works fine to configure them that they directly relay the COMPX_OUTs to a predefined, but for each comparator separate and fixed GPIO (without any SW/ISR delay):

0690X00000ArSLDQA3.png

  • COMP1_OUT -> PA11
  • COMP2_OUT -> PA12

Due to my HW layout, I want to realize something like this configuration:

  • COMP1_OUT ⊕ COMP2_OUT -> PA11

or

  • COMP1_OUT ⊕ COMP2_OUT -> PA12

I have not found a way to directly connect both comparator outputs into one single output pin without introducing an SW/ISR delay/latency. I read that some general purpose timers offer a so called "Hall" encoder mode, which supports XOR-ing up to 3 input signals. But since connecting a Timer directly to a GPIO via DMA seems to be impossible on a STM32L0-core, I have no idea how to implement this...

Does anyone know a "hardware/fast way" to route/XOR simultaneously both COMP_OUTs of a STM32L0x2 to a single GPIO output pin (either PA11 or PA12) or is it in that case inevitable, to use an ISR-based solution (the HW-layout is fixed and cannot be changed)?

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1 reply

waclawek.jan
waclawek.jan
Super User
November 3, 2019

Maybe this could be pulled out by

  • setting TIM2_OR.TI4_RMP to 0b01: TIM2 TI4 input connected to COMP2_OUT
  • setting CH4 in TIM2_CCMR2 to input capture from its "native" input,
  • setting CH4 to capture at both edges in TIM2_CCER by setting both CC4P and CC4NP
  • enabling CH4 by setting CC4E
  • enabling DMA requests from CH4 by setting TIM4_DIER.CC4DE
  • selecting TIM2_CH4 as trigger for DMA channel 4
  • setting up DMA channel 4 to DMA from a buffer in memory to COMP1_CSR, circular mode, NDTR set to 2
  • storing to the buffer in memory from which DMA runs, values for COMP1_CSR so that they have alternating values for COMP1POLARITY

and that's roughly it.

It is a bit fragile in that it needs to be started when COMP2OUT has the proper polarity, and edges in COMP2 must be far enough apart each other so that the whole mechanism succeeds to write the proper value into COMP1_CSR for each edge.

JW

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