Unable to connect to STM32N657 after remapping BOOT1 from PA6 to PN10

[CHACHA]

Hello,

I am using an STM32N657 on a custom board.

I need to use PA6 as PIXCLK, so I would like to move the BOOT1 function from the default PA6 pin to PN10.

According to the STM32N6 BootROM/OTP description, I understood that BOOT1 can be remapped using OTP19 (BOOTROM_CONFIG_10):

 

I programmed OTP19 with 0x15200000 in STM32CubeProgrammer to change BOOT1 from PA6 to PN10.

Before programming OTP19, I could connect to the MCU normally through ST-LINK/SWD using PA6 as BOOT1.

However, after programming OTP19 to 0x15200000, I can no longer connect to the MCU.

The same issue has occurred on more than one custom board.

My test conditions are:

• MCU: STM32N657
• I/O supply voltage: 1.8 V
• BOOT1 remapped to: PN10
• OTP19 programmed value: 0x15200000
• PN10 is held HIGH before and during reset
• ST-LINK detects the target voltage
• During connection, STM32CubeProgrammer can sometimes identify Device ID 0x486, but then reports that the connection to device 0x486 is lost
• The board works and SWD connection is available before changing BOOT1 from PA6 to PN10

Could you please confirm the following?

1. Is OTP19 = 0x15200000 the correct value for remapping BOOT1 to PN10 on STM32N657?
2. Are there any additional OTP settings required before using PN10 as BOOT1 when VDDIO3 is 1.8 V?
3. Is there any known limitation or issue when using PN10 as the Development BOOT1 pin?
4. After programming OTP19, is a specific power-cycle/reset sequence required for the new BOOT1 pin assignment to become effective?
5. Is there any recovery method if the MCU can no longer enter Development Boot or connect through SWD after this OTP19 change?

I would appreciate it if you could also provide the recommended OTP configuration and programming sequence for changing BOOT1 from PA6 to PN10.

Best regards,

 

 

[mƎALLEm]

Hello ​@CHACHA and welcome to the ST community,

The same question has been asked in this post:

The question has been already raised internally for review over the internal ticket CDM0065901 & CDM0065903  (not accessible by the community users).

[mƎALLEm]

Hello ​@CHACHA  and sorry for the late delay,

Our answer:

Here is a preliminary information while waiting for doc update.

UM3234/DS14791 and RM0486 (will be updated later) will be update with this content (approximate content for information only):

The BootROM is the first code executed after any system reset. The boot mode is determined by BOOT0 and BOOT1 pins, one OTP word (flash source selection), and one TAMP backup register.

• BOOT0 is a dedicated pin latched upon reset release

• BOOT1 is a non-dedicated boot pin. Its value can be sourced either from the default BOOT1 pin or from another GPIO from VDD power domain selected through the OTP system configuration (refer next table).

By default, PA6 is assigned as the BOOT1 input and is managed through the alternate function mechanism together with the SYSCFG_BOOTR register.

When another GPIO is selected as the BOOT1 source through the corresponding OTP configuration, the BOOT1 function on PA6 is masked and the input state of the selected GPIO is used instead and its pull-down default state remain enabled. 

Table1 BOOT1 available pins (package-specific pin availability not considered) 

PORTA	PORTB	PORTC	PORTD	PORTE	PORTF	PORTG	PORTH	PORTN	PORTO	PORTP	PORTQ
PA0	PB0	-	PD0	PE0	PF0	PG0	PH0	-	-	-	PQ0
PA1	PB1	-	PD1	PE1	PF1	PG1	PH1	-	-	-	PQ1
PA2	PB2	-	PD2	PE2	PF2	PG2	-	-	-	-	PQ2
PA3	PB3	-	PD3	PE3	PF3	PG3	PH3	-	-	-	PQ3
PA4	PB4	-	PD4	-	PF4	PG4	PH4	-	-	-	PQ4
PA5	PB5	-	PD5	PE5	PF5	PG5	PH5	-	-	-	PQ5
PA6(1)	PB6	-	PD6	PE6	PF6	PG6	PH6	-	-	-	PQ6
PA7	PB7	-	PD7	PE7	PF7	PG7	PH7	-	-	-	PQ7
PA8	PB8	-	PD8	PE8	PF8	PG8	PH8	-	-	-	-
PA9	PB9	-	PD9	PE9	PF9	PG9	-	-	-	-	-
PA10	PB10	-	PD10	PE10	PF10	PG10	-	-	-	-	-
PA11	PB11	-	PD11	PE11	PF11	PG11	-	-	-	-	-
PA12	PB12	-	PD12	PE12	PF12	PG12	-	-	-	-	-
PA13	PB13	PC13	PD13	PE13	PF13	PG13	-	-	-	-	-
PA14	PB14	PC14	PD14	PE14	PF14	PG14	-	-	-	-	-
PA15	PB15	PC15	PD15	PE15	PF15	PG15	-	-	-	-	-

 

(1) Default BOOT1 pin

Hope that answers your question.