topic unaligned memory access fault on S32K312 with MCAL RTD 3.0.0 in S32K

unaligned memory access fault on S32K312 with MCAL RTD 3.0.0

Hudson001 — Wed, 12 Jun 2024 05:18:03 GMT

Hello,

I have a unaligned memory access fault on S32K312 with MCAL RTD 3.0.0.

The issue description :

With Autoever Autosar V2.0.0 SWP release, OS reset happened which is caused by unaligned memory access fault.
The fault always happened when a global variable is defined in system RAM area of 0x2040C000~0x20418000.
In system RAM area of 0x20404000~20407fff, there is no this fault.
In DTCM area, there is no this fault.
I have checked the UNALIGN_TRP bit of Arm Cortex-m7 CCR register, it's disabled in init, and checked when fault happening, it is zero, Trapping disabled.

I tested two ways of the unaligned memory access which would trigger the fault.

. Way-1, structure elements access in unaligned memory

typedef struct {
uint8 a;
uint32 b;
}unaligned_test_t;

attribute((section(".SYSRAM_2040B000"))) unaligned_test_t unaligned_test_data_sram_2040B000;
attribute((section(".SYSRAM_2040C000"))) unaligned_test_t unaligned_test_data_sram_2040C000;

void unaligned_test(void)

{
unaligned_test_data_sram_2040B000.b = 0x10; // no unaligned access error.
unaligned_test_data_sram_2040C000.b = 0x10; // unaligned access error happened.
}

. Way-2, array access in unaligned memory

attribute((section(".SYSRAM_2040B000"))) uint8 unaligned_test_array_sram_2040B000;
attribute((section(".SYSRAM_2040C000"))) uint8 unaligned_test_array_sram_2040C000;

void unaligned_test(void){

uint32 * ptr;

for (uint32 i=0; i<16; i++)

{
ptr = (uint32 *)&unaligned_test_array_sram_2040B000[i];
*ptr = i; // no unaligned access error happened.
}

for (uint32 i=0; i<16; i++)

{
     ptr = (uint32 *)&unaligned_test_array_sram_2040C000[i];
     *ptr = i;               // no unaligned access error happened on offset 0,4,8,12
                             // unaligned access error happened on offset 1,2,3,5,6,7,9,10,11,13,14,15.
}

}

Re: unaligned memory access fault on S32K312 with MCAL RTD 3.0.0

Hudson001 — Wed, 12 Jun 2024 10:13:19 GMT

The issue disappeared after MPU init code masked, that means MPU disabled. So why the MPU would trigger the unaligned access issue? The MPU config is in below,

Region Description Start End Size[KB] permission attribute execute srd enable -------- ---------------------------- ---------- ---------- ---------- ------------------------ ------------------------ ------------------- ------ ---------- 0 BACKGROUND_REGION 0x0 0xFFFFFFFF 4194304 MPU_ACCESS_P_PRIV_RW MPU_ATTR_STR_ORD_DEV MPU_INST_ACCESS_DIS 0x00 MPU_ENABLE 1 CM7_SELF_ITCM_REGION 0x0 0x00007FFF 32 MPU_ACCESS_P_PRIV_RW MPU_ATTR_NORM_MEM_WT MPU_INST_ACCESS_EN 0x00 MPU_ENABLE 2 PROGRAM_FLASH_REGION_ADDR 0x00400000 0x005FFFFF 2048 MPU_ACCESS_P_PRIV_RO MPU_ATTR_NORM_MEM_WT MPU_INST_ACCESS_EN 0x00 MPU_ENABLE 3 DATA_FLASH_REGION_ADDR 0x10000000 0x1001FFFF 128 MPU_ACCESS_P_PRIV_RW MPU_ATTR_NORM_MEM_WT MPU_INST_ACCESS_DIS 0x00 MPU_ENABLE 4 CM7_SELF_DTCM_REGION_ADDR 0x20000000 0x2000FFFF 64 MPU_ACCESS_P_PRIV_RW MPU_ATTR_NORM_MEM_WT MPU_INST_ACCESS_DIS 0x00 MPU_ENABLE 5 SRAM_REGION_ADDR 0x20400000 0x20417FFF 96 MPU_ACCESS_P_PRIV_RW MPU_ATTR_NORM_MEM_WT MPU_INST_ACCESS_EN 0x00 MPU_ENABLE 6 PERI_REGISTER_REGION_ADDR 0x40008000 0x40807FFF 8192 MPU_ACCESS_P_PRIV_RW MPU_ATTR_SHR_DEV MPU_INST_ACCESS_DIS 0x00 MPU_ENABLE */ static const uint32 EcuM_Rbar[CPU_MPU_MEMORY_COUNT] = {0x00000000UL, 0x00000000UL, 0x00400000UL, 0x10000000UL, 0x20000000UL, 0x20400000UL, 0x40008000UL}; static const uint32 EcuM_Rasr[CPU_MPU_MEMORY_COUNT] = {0x1100003FUL, 0x0102001DUL, 0x05020029UL, 0x11020021UL, 0x1102001FUL, 0x0102F821UL, 0x1101002DUL};

Re: unaligned memory access fault on S32K312 with MCAL RTD 3.0.0

danielmartynek — Thu, 13 Jun 2024 12:19:32 GMT

Hi @Hudson001,

In ARM®v7-M Architecture Reference Manual

Section A3.5.7 Memory access restrictions

You can read:

"An instruction that generates an unaligned memory access to Device or Strongly-ordered memory is
UNPREDICTABLE."

Here are the definitions of the memory types:

https://developer.arm.com/documentation/dui0646/c/Cortex-M7-Peripherals/Optional-Memory-Protection-Unit/MPU-access-permission-attributes

Regards,

Daniel

Re: unaligned memory access fault on S32K312 with MCAL RTD 3.0.0

Hudson001 — Fri, 14 Jun 2024 06:09:52 GMT

Thank you Daniel,

But still not clear why the unaligned error happened on system ram address >=0x2040c000, the MPU setting seems applied on whole sysRam 0x20400000 with MPU Rasr register value 0x0102F821

Re: unaligned memory access fault on S32K312 with MCAL RTD 3.0.0

danielmartynek — Fri, 14 Jun 2024 14:07:23 GMT

I see, it is a normal type memory.

I have just reproduced the error using your RASR value.

In my test project, there are only 2 regions, this one and one that covers the whole map (Strongly ordered)

Why do you enable the subregions there?

It works when the subregions are disabled, refer to ARM documentation.

Can you try this configuration?

Regards,

Daniel

Re: unaligned memory access fault on S32K312 with MCAL RTD 3.0.0

Hudson001 — Wed, 19 Jun 2024 10:37:25 GMT

Hi Daniel, I got understand the RASR register usage.

The MPU region size (RASR.Size) is defined as 2^(16+1) = 128KB, so each subregion is 128K/8 = 16K. On S32K312, SRAM is 96KB, so SRD bit of RASR should be 0xC0, subregion 7,6 disabled, subregion 5-0 enabled.

I tested RASR with value of 0x01020021 and 0x0102C021, both worked, unaligned error did not happen on whole SRAM region of 0x20400000~0x20417FFF.

Thanks for your great support^^

regards,

Hudson