Overview
13-5
USB Function Module
13.1.3 USB Function Clocks and Reset
The USB function has two clocks:
-
An interface clock (CLOCK_I), used between the MPU TIPB and the USB
function and connected to the MPU peripheral programmable clock
(PERCLK), is derived by dividing CK_GEN1 (the output of DPLL1) by the
value associated with the PERDIV field of the ARM_CKCTL register
(0xFFFECE00).
This is a free-running clock when the system is awake.
-
A 48-MHz functional clock (CLK_48_I), which is generated by the ULPD
DPLL.
This clock can be shutdown by the USB function (DISABLE_CLK48_O)
when:
J
The USB is suspended (idle state).
J
The USB is disconnected.
This shutdown must be enabled beforehand: Set SOFF_Dis (bit 1), of the
SYSCON1 register to 0 (default value).
The MPU TIPB reset (MPU_PER_RST) resets the USB function.
13.1.4 USB Function DMA Requests
The USB function can use:
-
Three receive DMA channels (DMA_RX_REQ_ON [2:0]): Any endpoint
number (1:15) can be selected to be assigned to one receive DMA
channel.
The DMA_RX_REQ_ON [2:0] are connected to the system DMA request
[27:25].
-
Three transmit DMA channels (DMA_TX_REQ_ON [2:0]): any endpoint
number (1:15) can be selected to be assigned to one transmit DMA
channel.
The DMA_TX_REQ_ON [2:0] are connected to the system DMA request
[30:28].
