Hw Flow Control - STMicroelectronics STM32F405 Reference Manual

Secure digital input/output interface (SDIO)
31.8

HW flow control

The HW flow control functionality is used to avoid FIFO underrun (TX mode) and overrun
(RX mode) errors.
The behavior is to stop SDIO_CK and freeze SDIO state machines. The data transfer is
stalled while the FIFO is unable to transmit or receive data. Only state machines clocked by
SDIOCLK are frozen, the APB2 interface is still alive. The FIFO can thus be filled or emptied
even if flow control is activated.
To enable HW flow control, the SDIO_CLKCR[14] register bit must be set to 1. After reset
Flow Control is disabled.
31.9 SDIO registers
The device communicates to the system via 32-bit-wide control registers accessible via
APB2.
The peripheral registers have to be accessed by words (32 bits).
31.9.1 SDIO power control register (SDIO_POWER)
Address offset: 0x00
Reset value: 0x0000 0000
31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10
Bits 31:2 Reserved, must be kept at reset value
Bits 1:0 PWRCTRL: Power supply control bits.
Note: At least seven HCLK clock periods are needed between two write accesses to this register.
After a data write, data cannot be written to this register for three SDIOCLK (48 MHz) clock
periods plus two PCLK2 clock periods.
1052/1731
These bits are used to define the current functional state of the card clock:
00: Power-off: the clock to card is stopped.
01: Reserved
10: Reserved power-up
11: Power-on: the card is clocked.
DocID018909 Rev 11
Reserved
9 8 7 6 5 4 3
RM0090
2 1 0
PWRC
TRL
rw rw