OpenE2K/qemu-e2k
13
4
Fork 0
Code Issues 4 Pull Requests Projects 2 Releases Activity

hw/net/stellaris_enet: Correctly implement the TR and THR registers

Browse Source 
Packet transmission for the stellaris ethernet controller can be triggered
in one of two ways:
 * by setting a threshold value in the THR register; when the FIFO
   fill level reaches the threshold, the h/w starts transmitting.
   Software has to finish filling the FIFO before the transmit
   process completes to avoid a (silent) underrun
 * by software writing to the TR register to explicitly trigger
   transmission

Since QEMU transmits packets instantaneously (from the guest's
point of view), implement "transmit based on threshold" with
our existing mechanism of "transmit as soon as we have the whole
packet", with the additional wrinkle that we don't transmit if
the packet size is below the specified threshold, and implement
"transmit by specific request" properly.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
This commit is contained in:
Peter Maydell 2014-05-13 16:09:37 +01:00
parent c6fa443b3d
commit a9171c4fb5
1 changed files with 15 additions and 2 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

17
hw/net/stellaris_enet.c
View File

@ -109,6 +109,15 @@ static inline bool stellaris_txpacket_complete(stellaris_enet_state *s)
return s->tx_fifo_len >= framelen;
}
/* Return true if the TX FIFO threshold is enabled and the FIFO
* has filled enough to reach it.
*/
static inline bool stellaris_tx_thr_reached(stellaris_enet_state *s)
{
return (s->thr < 0x3f &&
(s->tx_fifo_len >= 4 * (s->thr * 8 + 1)));
}
/* Send the packet currently in the TX FIFO */
static void stellaris_enet_send(stellaris_enet_state *s)
{
@ -309,7 +318,7 @@ static void stellaris_enet_write(void *opaque, hwaddr offset,
s->tx_fifo[s->tx_fifo_len++] = value >> 24;
}
if (stellaris_txpacket_complete(s)) {
if (stellaris_tx_thr_reached(s) && stellaris_txpacket_complete(s)) {
stellaris_enet_send(s);
}
break;
@ -338,9 +347,13 @@ static void stellaris_enet_write(void *opaque, hwaddr offset,
case 0x2c: /* MTXD */
s->mtxd = value & 0xff;
break;
case 0x38: /* TR */
if (value & 1) {
stellaris_enet_send(s);
}
break;
case 0x30: /* MRXD */
case 0x34: /* NP */
case 0x38: /* TR */
/* Ignored. */
case 0x3c: /* Undocuented: Timestamp? */
/* Ignored. */