topic Strange problem with multiple frame buffer in i.MX RT Crossover MCUs

Strange problem with multiple frame buffer

mail10 — Tue, 09 Mar 2021 09:05:39 GMT

We are using the MCUXpresso IDE (V 11.2., SDK 2.8.2, emwin library 6.1) for an IMXRT1062 project (Embedded Artists iMX RT1062 OEM IT module).

When using multiple frame buffers for the display driver, the program abort sometimes the normal processing and runs only in the this routine (in core_cm7.h) which cleans the buffer cache. This could happen after seconds up to many minutes after program start.

With a single frame buffer the program runs fine, but there are some disturbance in the display.

/**
\brief Clean & Invalidate D-Cache
\details Cleans and Invalidates D-Cache
*/
__STATIC_FORCEINLINE void SCB_CleanInvalidateDCache (void)
{
#if defined (__DCACHE_PRESENT) && (__DCACHE_PRESENT == 1U)
uint32_t ccsidr;
uint32_t sets;
uint32_t ways;

SCB->CSSELR = 0U; /* select Level 1 data cache */
__DSB();

ccsidr = SCB->CCSIDR;

/* clean & invalidate D-Cache */
sets = (uint32_t)(CCSIDR_SETS(ccsidr));
do {
ways = (uint32_t)(CCSIDR_WAYS(ccsidr));
do {
SCB->DCCISW = (((sets << SCB_DCCISW_SET_Pos) & SCB_DCCISW_SET_Msk) |
((ways << SCB_DCCISW_WAY_Pos) & SCB_DCCISW_WAY_Msk) );
#if defined ( __CC_ARM )
__schedule_barrier();
#endif
} while (ways-- != 0U);
} while(sets-- != 0U);

__DSB();
__ISB();
#endif
}

The frame buffer is located in the SDRAM:

Memory region Used Size Region Size %age Used
BOARD_FLASH: 480560 B 4 MB 11.46%
BOARD_SDRAM: 5603656 B 30 MB 17.81%
NCACHE_REGION: 16440 B 2 MB 0.78%
SRAM_DTC: 0 GB 128 KB 0.00%
SRAM_ITC: 0 GB 128 KB 0.00%
SRAM_OC: 0 GB 768 KB 0.00%

Best regards,

Reiner

Re: Strange problem with multiple frame buffer

FelipeGarcia — Thu, 11 Mar 2021 18:44:22 GMT

Hi Reiner,

We have identified some issues when placing buffers in a cacheable region like OCRAM or SDRAM. To use SDRAM for this you will need to split a non-cacheable region to place the buffers.

Please check the below community document written by a colleague that explains this behavior in detail.

Using NonCached Memory on i.MXRT - NXP Community

Best regards,

Felipe

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Re: Strange problem with multiple frame buffer

mail10 — Tue, 16 Mar 2021 14:33:03 GMT

Thank you, now the program is running fine.

Best regards,

Reiner