Hello All,
I have a few questions for the USB device driver regarding the setup.
1. In at91_udc.c from maxim.org 2.6.12 patch (which is the kernel I am
using) in the at91_ep_enable function there is code which limits the max
packet buffer to 64...
case USB_ENDPOINT_XFER_INT:
if (maxpacket > 64)
goto bogus_max;
break;
case USB_ENDPOINT_XFER_BULK:
switch (maxpacket) {
case 8:
case 16:
case 32:
case 64:
goto ok;
I understand this as the Atmel datasheet says that for endpoints that
use the provided ping-pong buffers, the maximum supported is 64 bytes.
Then I noticed under the ep definitions, 45 and five say they have a max
packet of 256...
.ep[4] = {
.ep = {
.name = "ep4",
.ops = &at91_ep_ops,
},
.udc = &controller,
.is_pingpong = 1,
.maxpacket = 256,
.creg = UDC_REG32(0x40),
.int_mask = 1 << 4,
},
.ep[5] = {
.ep = {
.name = "ep5",
.ops = &at91_ep_ops,
},
.udc = &controller,
.is_pingpong = 1,
.maxpacket = 256,
.creg = UDC_REG32(0x44),
.int_mask = 1 << 5,
Why is this?
2. Is it even worth considering changing these from a peripheral backed
ping-pong buffer style to a non peripheral backed buffer that allows for
larger transfers, or would it be much slower?
3. At the end of the ep definition struct there is this comment...
/* ep6 and ep7 are also reserved */
Does anyone know if this means they are available and just not declared
due to older hardware compatibility, or can they not be used by the
driver for some other reason? The AT91RM9200 data sheet shows that they
could potentially be used.
4. I noticed that the serial driver (serial.c) allocates 64 bytes for
each urb buffer it queues, whereas the zero driver (zero.c) allocates
4096 for each urb. If my system only allows a max packet of 64, thats
all one urb can hold right? When I look at the function read_fifo in
at91_udc.c, from what I read, it will only fill to the maxpacket size
even if the buffer size of the urb is larger (I think...).
Thank you for looking at this.
Regards,
Jeff Warren
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