Host Channels - ST STM32F412 Reference Manual

RM0402
29.7.3

Host channels

The OTG_FS core instantiates 12 host channels. Each host channel supports an USB host
transfer (USB pipe). The host is not able to support more than 12 transfer requests at the
same time. If more than 12 transfer requests are pending from the application, the host
controller driver (HCD) must re-allocate channels when they become available from
previous duty, that is, after receiving the transfer completed and channel halted interrupts.
Each host channel can be configured to support in/out and any type of periodic/nonperiodic
transaction. Each host channel makes us of proper control (OTG_HCCHARx), transfer
configuration (OTG_HCTSIZx) and status/interrupt (OTG_HCINTx) registers with
associated mask (OTG_HCINTMSKx) registers.
Host channel control
• The following host channel controls are available to the application through the host
channel-x characteristics register (OTG_HCCHARx):
–
–
–
–
–
–
–
–
Host channel transfer
The host channel transfer size registers (OTG_HCTSIZx) allow the application to program
the transfer size parameters, and read the transfer status. Programming must be done
before setting the channel enable bit in the host channel characteristics register. Once the
endpoint is enabled the packet count field is read-only as the OTG_FS core updates it
according to the current transfer status.
•
The following transfer parameters can be programmed:
–
–
–
Host channel status/interrupt
The host channel-x interrupt register (OTG_HCINTx) indicates the status of an endpoint
with respect to USB- and AHB-related events. The application must read these register
when the host channels interrupt bit in the core interrupt register (HCINT bit in
OTG_GINTSTS) is set. Before the application can read these registers, it must first read the
host all channels interrupt (OTG_HAINT) register to get the exact channel number for the
host channel-x interrupt register. The application must clear the appropriate bit in this
register to clear the corresponding bits in the OTG_HAINT and OTG_GINTSTS registers.
Channel enable/disable
Program the FS/LS speed of target USB peripheral
Program the address of target USB peripheral
Program the endpoint number of target USB peripheral
Program the transfer IN/OUT direction
Program the USB transfer type (control, bulk, interrupt, isochronous)
Program the maximum packet size (MPS)
Program the periodic transfer to be executed during odd/even frames
transfer size in bytes
number of packets making up the overall transfer size
initial data PID
USB on-the-go full-speed (OTG_FS)
RM0402 Rev 6 981/1163
1122