DE1-SOC: Baremetal SDCARD reading performance

[Altera_Forum]

Hi, 

 I try to improve our SDCard reading performance.  I have tested the speed of sdcard that we will use on our project, and windows can write a big file to it with 10MB/sec and read back with around 20MB/sec.  When I plug same card into DE1-SOC board, I can read only 1.58 MB/sec. And this is after enabling cache, mmu and use high speed setting for MMC interface.  Here is my MMU and MMC settings: void mmu_init(void) { uint32_t *ttb1 = NULL; /* Populate the page table with sections (1 MiB regions). */ ALT_MMU_MEM_REGION_t regions = { /* Memory area: 1 GiB */ { .va = (void *)0x00000000, .pa = (void *)0x00000000, .size = 0x40000000, .access = ALT_MMU_AP_FULL_ACCESS, .attributes = ALT_MMU_ATTR_DEVICE_NS, // ALT_MMU_ATTR_WBA causes SD card fail at reading, why?? .shareable = ALT_MMU_TTB_S_NON_SHAREABLE, .execute = ALT_MMU_TTB_XN_DISABLE, .security = ALT_MMU_TTB_NS_SECURE }, /* Device area: Everything else */ { .va = (void *)0x40000000, .pa = (void *)0x40000000, .size = 0xc0000000, .access = ALT_MMU_AP_FULL_ACCESS, .attributes = ALT_MMU_ATTR_DEVICE_NS, .shareable = ALT_MMU_TTB_S_NON_SHAREABLE, .execute = ALT_MMU_TTB_XN_ENABLE, .security = ALT_MMU_TTB_NS_SECURE } }; alt_mmu_init(); alt_mmu_va_space_storage_required(regions, sizeof(regions)/sizeof(regions)); alt_mmu_va_space_create(&ttb1, regions, sizeof(regions)/sizeof(regions), alt_pt_alloc, alt_pt_storage); alt_mmu_va_space_enable(ttb1); } void init_mmc(void) { ALT_STATUS_CODE status = ALT_E_SUCCESS; ALT_SDMMC_CARD_MISC_t card_misc_cfg; print_debug("MMC Initialization.\n"); alt_globaltmr_int_is_enabled(); alt_sdmmc_init(); alt_sdmmc_card_pwr_on(); alt_sdmmc_card_identify(&Card_Info); // Card_Info.card_type == ALT_SDMMC_CARD_TYPE_SDHC alt_sdmmc_card_bus_width_set(&Card_Info, ALT_SDMMC_BUS_WIDTH_4); alt_sdmmc_fifo_param_set((ALT_SDMMC_FIFO_NUM_ENTRIES >> 3) - 1, (ALT_SDMMC_FIFO_NUM_ENTRIES >> 3), ALT_SDMMC_MULT_TRANS_TXMSIZE1); alt_sdmmc_card_misc_get(&card_misc_cfg); alt_sdmmc_dma_enable(); alt_sdmmc_card_speed_set(&Card_Info, (Card_Info.high_speed ? 2 : 1) * Card_Info.xfer_speed); // switch to high speed }  What can I do to improve sdcard reading performance? (windows reads 13 times faster)  Thanks.