topic iMX6 MMU and Cache Initialization Sequence in i.MX Processors

iMX6 MMU and Cache Initialization Sequence

ogj — Tue, 09 Mar 2021 06:09:56 GMT

I’m trying to determine the correct order in initializing the caches and mmu at power up for the iMX6 Quad. This is for a custom OS. This is what I have so far:

_int_disable();

// Disable the mmu if it is enabled (shouldn't be enabled on powerup)

_mmu_disable();

// Disable the icache, dcache and L2 cache

_L1_dcache_disable();

_L1_icache_disable();

if(_l2c310_cache_sts())

_l2c310_disable();

// Invalidate dcache, and L2 cache – what about the icache???

_dcache_invalidate(); // invalidates L1_dcache and L2 cache

// Allocate the memory for the mmu Section Table

L1_TBL_ptr = _mem_alloc_align(MMU_L1_TBL_SIZE, MMU_L1_TBL_ALIGN);

// Clear the mmu table

_mem_zero(L1_TBL_ptr, MMU_L1_TBL_SIZE);

// Initialize the mmu

// - Map all of memory space to 1 MB sections, strongly ordered, RW, shared

// - Remap sections that are actually used – DDR, SRAM

_mmu_init();

// Initialize the mmu

// - Map all of memory space to 1 MB sections, strongly ordered, RW, shared

// - Remap sections that are actually used

_mmu_init();

// Enable the mmu

// - Save the address of the mmu table in the TTBR0

// - Write the DACR register – 0x55555555

// - Invalidate the TLB (including DSB and ISB following)

// - Enable the MMU

_mmu_enable();

DSB;

ISB;

// Enable the caches

_l1_dcache_enable();

_int_enable();

At this point there is a prefetch error, and I can’t get beyond here.

Somewhere up above the sequence of everything is messed up. The mmu is set up flat-mapped; va = pa

Things I don’t know how to put into the sequence:

Invalidating and enabling the branch prediction cache
Enabling the dcache prefetch

I’ve looked at the SDK, including the patch to add L2 cache to SDK, however this crashes as well as soon as the dcache is enabled.

Any ideas??

Re: iMX6 MMU and Cache Initialization Sequence

igorpadykov — Tue, 09 Mar 2021 07:34:16 GMT

Hi ogj

one can look at sdk codes (1.1.0_iMX6_Platform_SDK.zip)

https://community.nxp.com/t5/i-MX-Processors/SMP-Enable-in-IMX6/m-p/542111

https://community.nxp.com/t5/i-MX-Processors-Knowledge-Base/Enabling-MMU-and-Caches-on-i-MX6-Series-Platform-SDK/ta-p/1108712

Best regards
igor

Re: iMX6 MMU and Cache Initialization Sequence

ogj — Wed, 17 Mar 2021 04:52:05 GMT

I couldn't get the SDK version working, but I did get everything working by experimentation.

I do have another question about the SDK cache patch. In the patch there is the following PL310 setup:

/*******************************************************************************
* Function: _l2c310_cache_setup
* Comments:
* This function sets up reg1_tag_ram_control & reg1_data_ram_control
* and enables double line fill in the L2 cache controller
*******************************************************************************/

void _l2c310_cache_setup(void)
{
CA5L2C_reg1_tag_ram_control = 0x00000132u; //offset 0x108
CA5L2C_reg1_data_ram_control = 0x00000132u; //offset 0x10C
CA5L2C_reg15_prefetch_ctrl = 0x40800000u; //offset 0xF60

return;
}

Going through the PL310 Cache Controller TRM (Rev r0p0), none of these registers exist. Were they added by NXP? Is there any documentation on them? Everything works fine without calling that function.