USB on-the-go full-speed/high-speed (OTG_FS/OTG_HS) RM0390
1102/1328 RM0390 Rev 4
Device RxFIFO =
(4 * number of control endpoints + 6) + ((largest USB packet used / 4) + 1 for status
information) + (2 * number of OUT endpoints) + 1 for Global NAK
Example: The MPS is 1,024 bytes for a periodic USB packet and 512 bytes for a non-
periodic USB packet. There are three OUT endpoints, three IN endpoints, one control
endpoint, and three host channels.
Device RxFIFO = (4 * 1 + 6) + ((1,024 / 4) +1) + (2 * 4) + 1 = 276
Transmit FIFO RAM allocation: the minimum RAM space required for each IN endpoint
Transmit FIFO is the maximum packet size for that particular IN endpoint.
Note: More space allocated in the transmit IN endpoint FIFO results in better performance on the
USB.
Host mode
Receive FIFO RAM allocation:
Status information is written to the FIFO along with each received packet. Therefore, a
minimum space of (largest packet size / 4) + 1 must be allocated to receive packets. If
multiple isochronous channels are enabled, then at least two (largest packet size / 4) + 1
spaces must be allocated to receive back-to-back packets. Typically, two (largest packet
size / 4) + 1 spaces are recommended so that when the previous packet is being transferred
to the CPU, the USB can receive the subsequent packet.
Along with the last packet in the host channel, transfer complete status information is also
pushed to the FIFO. So one location must be allocated for this.
Host RxFIFO = (largest USB packet used / 4) + 1 for status information + 1 transfer
complete
Example: Host RxFIFO = ((1,024 / 4) + 1) + 1 = 258
Transmit FIFO RAM allocation:
The minimum amount of RAM required for the host Non-periodic Transmit FIFO is the
largest maximum packet size among all supported non-periodic OUT channels.
Typically, two largest packet sizes worth of space is recommended, so that when the current
packet is under transfer to the USB, the CPU can get the next packet.
Non-Periodic TxFIFO = largest non-periodic USB packet used / 4
Example: Non-Periodic TxFIFO = (512 / 4) = 128
The minimum amount of RAM required for host periodic Transmit FIFO is the largest
maximum packet size out of all the supported periodic OUT channels. If there is at least one
isochronous OUT endpoint, then the space must be at least two times the maximum packet
size of that channel.
Host Periodic TxFIFO = largest periodic USB packet used / 4
Example: Host Periodic TxFIFO = (1,024 / 4) = 256
Note: More space allocated in the Transmit Non-periodic FIFO results in better performance on
the USB.
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