Let's say you want to use the TIM1 as your slave. You then go to the reference manual of the processor and look for the TIMx Internal trigger connection table in the section called: "TIM1 slave mode control register (TIM1_SMCR)".
This table will tell you that if you want to use the input of say TIM3 as your clock for the slave then as per the table you will find that under ITR2 you find TIM3. This means that for TIM1 used as a slave the internal input trigger source to select is ITR2 so that it listens to TIM3 as the source as shown in the TIMx Internal trigger connection table for the TIM1.
This means that in this particular case your internal source will be ITR2 so in STM23CubeMX you setup TIM1 as slave and set its trigger source to ITR2 so that it listens to TIM3 as the source clock for TIM1 behaving as slave mode.
Doing so when generating code STM32CubeMX generates this code:
sSlaveConfig.SlaveMode = TIM_SLAVEMODE_EXTERNAL1;
sSlaveConfig.InputTrigger = TIM_TS_ITR2;
if (HAL_TIM_SlaveConfigSynchro(&htim1, &sSlaveConfig) != HAL_OK)
{
Error_Handler();
}Let's say now that in the same application you want to use TIM15 as your slave and you also want to use the TIM3 as your clock source forthe TIM15 slave. This time you search for TIM15 control register 2 (TIM15_CR2) in the reference manual and you'll find the TIMx Internal trigger connection table for the TIM15.
In this case even though you're still using the same TIM3 as a source you need to use Input Trigger ITR1 as the internal trigger source so that TIM15 listens to TIM3 as its clock . You apply the same selections as before to the STM32CubeMX and it will generate the correct code for it just like before.
