Aksal/nuttx
3
1
Fork 1
mirror of https://github.com/apache/nuttx.git synced 2026-09-11 13:16:33 +00:00
Code Issues Projects Releases Packages Wiki Activity Actions 2

arch/arm/src/imxrt: Keep FlexCAN TX mailbox allocation in order.

Browse source 
imxrt_transmit() handed out the lowest free TX mailbox. FlexCAN breaks an
arbitration tie between mailboxes holding equal CAN IDs by taking the lowest
mailbox number, so refilling a just-drained low mailbox while older frames
are still pending in higher ones puts the newer frame on the wire first.
imxrt_txdone_work() re-polls after each individual TX completion, which is
exactly the condition that triggers it.

Every frame of a multi-frame transport transfer carries the same CAN ID, so
this reorders transfers. On a DroneCAN bus the receiver sees a broken toggle
bit and discards the transfer: measured on the wire, a 6-frame message from
an i.MX RT1176 failed 82% of the time, while a node on the same bus running
a different controller was flawless over the same capture.

Hand out a mailbox above every pending one instead, and wrap back to the
bottom only once the ring has drained. Ordering then holds for any transfer
length; the cost is that the ring stalls at a wrap rather than refilling
immediately.

Assisted-by: Claude:claude-opus-5
Signed-off-by: Jacob Dahl <dahl.jakejacob@gmail.com>
This commit is contained in:
Jacob Dahl 2026-08-24 11:30:48 -06:00 • committed by Xiang Xiao
parent 80d432051a
commit e6696d5d27
1 changed files with 53 additions and 36 deletions
Download patch file Download diff file Expand all files Collapse all files

89
arch/arm/src/imxrt/imxrt_flexcan.c
View file

@ -516,6 +516,50 @@ static void imxrt_reset(struct imxrt_driver_s *priv);
* Private Functions
****************************************************************************/
/****************************************************************************
* Function: imxrt_txmb_next
*
* Description:
* Pick the mailbox to load the next frame into.
*
* Every frame of a multi-frame transport transfer carries the same CAN
* ID, and FlexCAN breaks an arbitration tie between mailboxes holding
* equal IDs by taking the lowest mailbox number. Handing out the
* lowest *free* mailbox therefore lets a frame loaded into a
* just-drained low mailbox win arbitration against older frames still
* pending in higher ones, and the receiver sees the transfer out of
* order.
*
* Only ever hand out a mailbox above every pending one, and wrap back to
* the bottom once the ring has drained.
*
* Input Parameters:
* priv - Reference to the driver state structure
*
* Returned Value:
* The mailbox index to use, or TOTALMBCOUNT if none is available.
*
****************************************************************************/
static uint32_t imxrt_txmb_next(struct imxrt_driver_s *priv)
{
uint32_t mbi = RXMBCOUNT + 1;
uint32_t next = RXMBCOUNT + 1;
while (mbi < TOTALMBCOUNT)
{
struct mb_s *mb = flexcan_get_mb(priv, mbi);
if (mb->cs.code == CAN_TXMB_DATAORREMOTE)
{
next = mbi + 1;
}
mbi++;
}
return next;
}
/****************************************************************************
* Function: imxrt_txringfull
*
@ -533,21 +577,7 @@ static void imxrt_reset(struct imxrt_driver_s *priv);
static bool imxrt_txringfull(struct imxrt_driver_s *priv)
{
uint32_t mbi = RXMBCOUNT + 1;
struct mb_s *mb;
while (mbi < TOTALMBCOUNT)
{
mb = flexcan_get_mb(priv, mbi);
if (mb->cs.code != CAN_TXMB_DATAORREMOTE)
{
return 0;
}
mbi++;
}
return 1;
return imxrt_txmb_next(priv) >= TOTALMBCOUNT;
}
/****************************************************************************
@ -586,34 +616,21 @@ static int imxrt_transmit(struct imxrt_driver_s *priv)
uint32_t txmb = 0;
#endif
mbi = RXMBCOUNT + 1;
mb_bit = 1 << mbi;
mbi = imxrt_txmb_next(priv);
while (mbi < TOTALMBCOUNT)
{
/* Check whether message buffer is not currently transmitting */
struct mb_s *mb = flexcan_get_mb(priv, mbi);
if (mb->cs.code != CAN_TXMB_DATAORREMOTE)
{
putreg32(mb_bit, priv->base + IMXRT_CAN_IFLAG1_OFFSET);
break;
}
mb_bit <<= 1;
mbi++;
#ifdef CONFIG_NET_CAN_RAW_TX_DEADLINE
txmb++;
#endif
}
if (mbi == TOTALMBCOUNT)
if (mbi >= TOTALMBCOUNT)
{
nwarn("No TX MB available mbi %" PRIi32 "\n", mbi);
NETDEV_TXERRORS(&priv->dev);
return 0; /* No transmission for you! */
}
mb_bit = 1 << mbi;
putreg32(mb_bit, priv->base + IMXRT_CAN_IFLAG1_OFFSET);
#ifdef CONFIG_NET_CAN_RAW_TX_DEADLINE
txmb = mbi - (RXMBCOUNT + 1);
#endif
#ifdef CONFIG_NET_CAN_RAW_TX_DEADLINE
struct timespec ts;
clock_systime_timespec(&ts);