The SDMMC_ACKTIMER register contains the acknowledgment timeout period, in SDMMC_CK bus clock periods. A counter loads the value from the SDMMC_ACKTIMER register, and starts decrementing when the data path state machine (DPSM) enters the Wait_Ack state. If the timer reaches 0 while the DPSM is in this states, the acknowledgment timeout status flag is set.
The SDMMC_CMDR register contains the command index and command type bits. The command index is sent to a card as part of a command message. The command type bits control the command path state machine (CPSM).
The SDMMC_DCNTR register loads the value from the data length register (see SDMMC_DLENR) when the DPSM moves from the Idle state to the Wait_R or Wait_S state. As data is transferred, the counter decrements the value until it reaches 0. The DPSM then moves to the Idle state and when there has been no error, the data status end flag (DATAEND) is set.
The SDMMC_DTIMER register contains the data timeout period, in card bus clock periods. A counter loads the value from the SDMMC_DTIMER register, and starts decrementing when the data path state machine (DPSM) enters the Wait_R or Busy state. If the timer reaches 0 while the DPSM is in either of these states, the timeout status flag is set.
The receive and transmit FIFOs can be only read or written as word (32-bit) wide registers. The FIFOs contain 16 entries on sequential addresses. This allows the CPU to use its load and store multiple operands to read from/write to the FIFO.When accessing SDMMC_FIFOR with half word or byte access an AHB bus fault is generated.
The SDMMC_IDMABASE0R register contains the memory buffer base address in single buffer configuration and the buffer 0 base address in double buffer configuration.
The receive and transmit FIFOs can be read or written as 32-bit wide registers. The FIFOs contain 32 entries on 32 sequential addresses. This allows the CPU to use its load and store multiple operands to read from/write to the FIFO.
The SDMMC_STAR register is a read-only register. It contains two types of flag:Static flags (bits [29,21,11:0]): these bits remain asserted until they are cleared by writing to the SDMMC interrupt Clear register (see SDMMC_ICR)Dynamic flags (bits [20:12]): these bits change state depending on the state of the underlying logic (for example, FIFO full and empty flags are asserted and de-asserted as data while written to the FIFO)