Hi all,
during the bring-up of the composite-cdcecm a alignment issue result in hard
faults (always on the used rp2040 based device).
ANALYSIS:
The root cause seems to be the way the pktbuf is defined in cdcecm_driver_s
(driver/usbdev/cdcecm.c):
struct cdcecm_driver_s
{
/* USB CDC-ECM device */
struct usbdevclass_driver_s usbdev; /* USB device class vtable */
struct usbdev_devinfo_s devinfo;
FAR struct usbdev_req_s *ctrlreq; /* Allocated control request */
FAR struct usbdev_ep_s *epint; /* Interrupt IN endpoint */
FAR struct usbdev_ep_s *epbulkin; /* Bulk IN endpoint */
FAR struct usbdev_ep_s *epbulkout; /* Bulk OUT endpoint */
uint8_t config; /* Selected configuration number */
uint8_t pktbuf[CONFIG_NET_ETH_PKTSIZE +
CONFIG_NET_GUARDSIZE];
Due to 'config‘ element ‚ pktbuf‘ in the structure is not aligned in anyway
from the struct itself.
The driver structure is allocation during driver initialization in
cdcecm_classobject():
/* Initialize the driver structure */
self = kmm_zalloc(sizeof(struct cdcecm_driver_s));
if (!self)
{
nerr("Out of memory!\n");
return -ENOMEM;
}
/* Network device initialization */
self->dev.d_buf = self->pktbuf;
As ’ self’ points to an aligned address, 'pktbuf' is always aligned at an odd
address.
Once the driver is initialized and processes received data in cdcecm_receive()
the driver creates a hard fault at:
#ifdef CONFIG_NET_IPv4
if (BUF->type == HTONS(ETHTYPE_IP))
{
BUF/eth_hdr_s are defined as:
#define BUF ((struct eth_hdr_s *)self->dev.d_buf)
struct eth_hdr_s
{
uint8_t dest[6]; /* Ethernet destination address (6 bytes) */
uint8_t src[6]; /* Ethernet source address (6 bytes) */
uint16_t type; /* Type code (2 bytes) */
};
Element ’ type’ is always odd aligned and access to it results in all cases to
a hard fault on the used rp2040 based board.
PROPOSAL:
Assuming the analysis is correct, there could be different options to fix there
issue.
Proposal would be to let the compiler do the job and not introduce any special
code or elements in the structure to fix it programmatically.
Analysing cdcdcm_driver_s in more details:
FAR struct usbdev_ep_s *epbulkout; /* Bulk OUT endpoint */
uint8_t config; /* Selected configuration number */
uint8_t pktbuf[CONFIG_NET_ETH_PKTSIZE +
CONFIG_NET_GUARDSIZE];
Element 'epbulkout' is a 32bit pointer and thus always aligned to 32bit.
Element 'config‘ following is also aligned to 32bit —> as it’s only an uint8_t
is doesn’t need to be aligned at all.
Element ‚pktbuf‘ is odd aligned, but needs to be at least 16bit aligned.
Exchanging 'config‘ and 'pktbuf‘ in the structure solves the issue:
FAR struct usbdev_ep_s *epbulkout; /* Bulk OUT endpoint */
uint8_t pktbuf[CONFIG_NET_ETH_PKTSIZE +
CONFIG_NET_GUARDSIZE];
uint8_t config; /* Selected configuration number */
Element ‚pktbuf‘ is now 32bit aligned as it’s following a 32bit pointer.
The change has been tested on an rp2040 based device.
The fix can be reviewed at:
https://github.com/ptka/incubator-nuttx/commit/01732850ad345b5e2a9af24f788935d8f7928781
<https://github.com/ptka/incubator-nuttx/commit/01732850ad345b5e2a9af24f788935d8f7928781>
Please comment on the analysis and proposed fix.
/Piet
