I run a boundary scan test (Goepel) on a design with an IMX6UL, a PMIC MC32PF3001, a Nand Flash, a DDR3 and some other glue.
When I test Nand Flash or DDR3 and if the test time is lower than about 5s, there is no problem.
If the test time is upper than about 5s (I decrease tester clock) , when the tester release the tap JTAG (state machin is in TLR- Test Logic Reset), immediatly the IMX6 drive a low on "PMIC_ON_REQ" (pin T9), so the PMIC is turned off, then it send a low state on POR_B (pin T8) of IMX6.
Port_B is a compliant pattern, it must be high to permit the control of JTAG tap. So, it's impossible to have control of the IMX through jtag bus.
To do that, the only way is to disconnect (hardware) the main power, and wait until discharge of all capacitors.
This problem doesn't appear on INFRA test, even if the tester wait 10 mn.
Thanks for your help.