Time to time, the driver needs to reset the hardware. It seems to appear when I disconnect then reconnect the wpa_cli (it is needed since the card is suddenly neither unable to send nor receive packets).
Here is (part of) the result contained in dmesg :
ath_hal: 0.9.18.0 (AR5210, AR5211, AR5212, RF5111, RF5112, RF2413, RF5413)
wlan: 0.8.4.2 (0.9.3.2)
ath_pci: 0.9.4.5 (0.9.3.2)
PCI: Enabling device 0000:00:0b.0 (0014 -> 0016)
ACPI: PCI Interrupt 0000:00:0b.0[A] -> GSI 19 (level, low) -> IRQ 20
ath_rate_sample: 1.2 (0.9.3.2)
wifi0: 11b rates: 1Mbps 2Mbps 5.5Mbps 11Mbps
wifi0: 11g rates: 1Mbps 2Mbps 5.5Mbps 11Mbps 6Mbps 9Mbps 12Mbps 18Mbps 24Mbps 36Mbps 48Mbps 54Mbps
wifi0: turboG rates: 6Mbps 12Mbps 18Mbps 24Mbps 36Mbps 48Mbps 54Mbps
wifi0: H/W encryption support: WEP AES AES_CCM TKIP
wifi0: mac 7.9 phy 4.5 radio 5.6
wifi0: Use hw queue 1 for WME_AC_BE traffic
wifi0: Use hw queue 0 for WME_AC_BK traffic
wifi0: Use hw queue 2 for WME_AC_VI traffic
wifi0: Use hw queue 3 for WME_AC_VO traffic
wifi0: Use hw queue 8 for CAB traffic
wifi0: Use hw queue 9 for beacons
wifi0: Atheros 5212: mem=0xdc800000, irq=20
ath0: no IPv6 routers present
ttyS1: LSR safety check engaged!
ttyS1: LSR safety check engaged!
agpgart: Found an AGP 3.5 compliant device at 0000:00:00.0.
agpgart: Putting AGP V3 device at 0000:00:00.0 into 8x mode
agpgart: Putting AGP V3 device at 0000:01:00.0 into 8x mode
wifi0: rx FIFO overrun; resetting
wifi0: ath_reset: unable to reset hardware: 'Hardware didn't respond as expected' (HAL status 3)
wifi0: rx FIFO overrun; resetting
wifi0: ath_reset: unable to reset hardware: 'Hardware didn't respond as expected' (HAL status 3)
wifi0: rx FIFO overrun; resetting
wifi0: ath_reset: unable to reset hardware: 'Hardware didn't respond as expected' (HAL status 3)
wifi0: rx FIFO overrun; resetting
wifi0: ath_reset: unable to reset hardware: 'Hardware didn't respond as expected' (HAL status 3)
...
The only way to use the card is then to reboot the computer.
I'm using a netgear WG311T wireless adapter with Linux 2.6.22.2 on a x86 computer.