mcf5272 Freescale Semiconductor, Inc, mcf5272 Datasheet - Page 289

• Manufacturer Part Number: mcf5272
• Description: Mcf5272 Coldfire Integrated Microprocessor User
• Manufacturer: Freescale Semiconductor, Inc

MOTOROLA
12.4.2 USB Configuration and Interface Changes
Although the USB module handles the SET_CONFIGURATION and SET_INTERFACE
requests, the user is still required to perform some initialization when the configuration or
alternate settings change. A configuration or alternate setting change is signaled by the
DEV_CFG interrupt. The following steps are required to service the DEV_CFG interrupt.
12.4.3 FIFO Configuration
The USB module allows a very flexible FIFO configuration. The FIFO configuration is very
application dependent. The FIFO configuration depends on the current configuration
number, alternate setting for each interface, and each endpoint’s type and packet size. The
USB module contains two separate 512-byte FIFO spaces: one for IN and one for OUT
endpoints. The following guidelines must be adhered to when configuring the FIFO’s:
1. Clear EP0CTL[CFG_RAM_VAL,USB_EN].
2. Load the configuration RAM with the descriptors from external ROM. The starting
3. Select the internal or external USB transceiver in EPC0TL.
4. Write IEP0CFG and OEP0CFG to initialize the EP0 IN and OUT FIFOs.
5. Initialize the EP0 interrupt vectors.
6. Clear all interrupt bits in EP0ISR.
7. Enable the desired EP0 interrupt sources in EP0IMR.
8. Set EP0CTL[USB_EN, CFG_RAM_VALID].
1. Read EPSR0 and ASR to determine the current configuration and alternate settings.
2. Read the endpoint descriptors for the current configuration and alternate settings to
3. Write EPnCFG for all active endpoints to initialize the FIFOs.
4. Initialize the interrupt vectors for the active endpoints.
5. Clear all interrupt bits in the EPnISR registers for all active endpoints.
6. Enable the desired interrupt sources in the EPnIMR registers.
7. Clear the DEV_CFG interrupt bit to allow the USB module to access the FIFOs.
• The MAX_PACKET field in the EPnCFG registers must match the
• EPnCFG[FIFO_SIZE] must be a power of 2 and must be at least two packets for
configuration RAM address is MBAR + 0x1400.
determine the endpoint type and maximum packet size for all of the active
endpoints.
wMaxPacketSize field in the corresponding endpoint descriptor. An incorrect setting
causes USB errors and unexpected interrupts.
non-isochronous endpoints.
Chapter 12. Universal Serial Bus (USB)
Software Architecture and Application Notes
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