STM32U375RETQ6 - Flash Erase succeeds but HAL_FLASH_Program causes BusFault
Hello,
I am using an STM32U375RETQ6 (512 KB Flash) and I am trying to erase and program the internal Flash using the STM32 HAL.
Environment
borad: customborad
Device: STM32U375RETQ6
STM32CubeIDE generated project(Ver2.2.0)
debugger: j-link
TrustZone disabled (TZEN = 0)
Dual Bank enabled (DUALBANK = 1)
Flash size confirmed as 512 KB (FLASHSIZE_BASE = 512)
Voltage Scaling: Range 1
Flash Latency: 3 Wait States
EPOD Booster enabled
MPU enabled, but no Flash region is configured
ICACHE disabled during Flash operations
Flash layout
Since this device has 512 KB Flash and Dual Bank is enabled:
Bank1: 0x08000000 - 0x0803FFFF
Bank2: 0x08040000 - 0x0807FFFF
Target programming address:
C
0x0807C000
which belongs to Bank2.
Erase operation
Flash erase completes successfully.
After erase, memory contents are correctly read back as:
0x0807C000 : FFFFFFFF FFFFFFFF ...
HAL_FLASHEx_Erase() returns HAL_OK.
No Flash error flags are reported.
Program operation
Programming fails inside the HAL function.
Call:
C
HAL_FLASH_Program(
FLASH_TYPEPROGRAM_DOUBLEWORD,
0x0807C000,
(uint32_t)wrbuf
);
The fault occurs inside:
C
static void FLASH_Program_DoubleWord(...)
{
SET_BIT((*reg_cr), FLASH_CR_PG);
*dest_addr = *src_addr; // BusFault here
}
Fault information
At the moment of the fault:
FLASH_CR = 0x40000001
FLASH_SR = 0x00000000
FLASH_SSR = 0x00000000
The PG bit is set and no Flash error flags are present.
CPU fault information:
CFSR = 0x00000082
HFSR = 0x40000000
BFAR = 0x0807C000
This indicates:
PRECISERR = 1
BFARVALID = 1
The BusFault occurs on the write access to address 0x0807C000.
Additional checks already performed
Flash unlock successful
Flash lock bit cleared
Voltage Scaling changed from Range2 to Range1
EPOD Booster enabled
Flash Latency increased to 3 WS
ICACHE disabled
Tested both FLASH_TYPEPROGRAM_DOUBLEWORD and FLASH_TYPEPROGRAM_BURST
Tested with fixed data patterns
Tested with local variables
Tested with static buffers
Tested with explicitly 8-byte aligned buffers using:
C
static uint32_t wrbuf[2] __attribute__((aligned(8)));
Confirmed that the problem is independent of the data content
Confirmed that the problem is independent of source buffer alignment
Tested both Bank1 and Bank2 target areas
MPU configuration checked
TrustZone disabled
WRP/HDP/SECWM protections checked and disabled
Flash erase succeeds correctly
FLASH_SR and FLASH_SSR remain zero even after the fault
Observation
The Flash erase operation works correctly, but the first Flash write access inside FLASH_Program_DoubleWord() immediately generates a BusFault before any Flash error flag is set.
Question
Why would a write to Flash generate a BusFault during the first store operation while:
erase succeeds,
PG bit is correctly set,
FLASH_SR and FLASH_SSR remain zero,
no protection mechanisms appear active,
and no Flash error flags are reported?
Is there any additional configuration or known condition required for Flash programming on STM32U375RETQ6 that could explain this behavior?
Thank you.