The SDIO interface on SN8205 is the BCM part interface but ST Micro controller interface (STM32F205). You can look at ST's data sheet for SDIO interface
SN8205 has no special limitation on the SDIO clock, and actually the SDIO clock is set to 48Mhz by default. The PLL clock input is 240MHz, PLL_Q=5, SDIO clock = 240/5 = 48Mhz.
Hope it helps.
Thanks for the reply.
SDIO clock is 48MHz, but prescaler (div by 2) is enabled by default, so actual clock is 24MHz.
Please look at Wiced\Platform\common\ARM_Cortex_M3\STM32F2xx\SDIO\wwd_bus.c,
function void host_platform_enable_high_speed_sdio( void );
Prescaler is enabled.
I found that there is very good reason to limit the SDIO clock output to 24MHz.
STM32F205 Errata sheet state that SDIO can not work with prescaler disabled (hardware bug).
There is a workaround (if USB and RNG are not used) to increase SDIO clock to 75MHz and leave the prescaler enabled.
Actual SDIO clock will be 37.5MHz. To achieve this, clock settings(PLL) must be altered.
Also, there is a disabled piece of code in wwd_bus_protocol.c file, which sets SDIO_SPEED_EHS bit in
SDIOD_CCCR_SPEED_CONTROL register, to allow higher than 25MHz clock to be used with the BCM.
I made everything and there was no problem with the communication at 37.5MHz SDIO clock, but
I doesn't like this configuration, because I'm planning to use USB in the future and the System Clock must remain
very low (75MHz).
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Hi ghouse, of course no.