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STM32WL5x: Undocumented Bug in IRTIM Module

AJ_1
Associate III

Hello,

I have been developing a program on the NUCLEO-WL55JC1 development board, and I found a bug in the IRTIM module. The reference manual says that, when enabled, the IRTIM module will NAND the outputs of TIM16 and TIM17 and output the signal on a pin. The bug I found is that if TIM17_BDTR.MOE is set before TIM16_BDTR.MOE is set, the IRTIM module outputs a high signal until TIM17 counts to TIM17_CCR1 for the first time. If TIM17_CCR1 is greater than TIM17_ARR, the output stays high forever.

I have attached a simple program that demonstrates the issue. It uses STM32 Low Level Drivers and is designed to run on a NUCLEO-WL55JC1. On this development board, the IR_OUT pin is connected to LED2, so you can see the IRTIM output signal. Both TIM16 and TIM17 are configured to always be high, and since IRTIM NANDs the signals together, LED2 should never turn on. However, when the program is initially run, LED2 is on until the first time TIM17 counts to CCR1.

I did not see this issue listed in the errata, so I'm assuming it's an unknown issue and wanted to report it to ST.

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