The system bus and chipidea IP have different limitations for
both host and device mode.
For example, with below errata, we need to enable SDIS(Stream Disable
Mode) at host mode. But we don't want it for device mode at the
same system.
TAR
9000378958
Title: Non-Double Word Aligned Buffer Address Sometimes Causes Host to
Hang on OUT Retry
Impacted Configuration: Host mode, all transfer types
Description:
The host core operating in streaming mode may under run while sending
the data packet of an OUT transaction. This under run can occur if
there are unexpected system delays in fetching the remaining packet
data from memory. The host forces a bad CRC on the packet, the device
detects the error and discards the packet. The host then retries a Bulk,
Interrupt, or Control transfer if an under run occurs according to the
USB specification. During simulations, it was found that the host does
not issue the retry of the failed bulk OUT. It does not issue any other
transactions except SOF packets that have incorrect frame numbers.
The second failure mode occurs if the under run occurs on an ISO OUT
transaction and the next ISO transaction is a zero byte packet. The host
does not issue any transactions (including SOFs). The device detects a
Suspend condition, reverts to full speed, and waits for resume signaling.
A third failure mode occurs when the host under runs on an ISO OUT and
the next ISO in the schedule is an ISO OUT with two max packets of 1024
bytes each. The host should issue MDATA for the first OUT followed by
DATA1 for the second. However, it drops the MDATA transaction, and
issues the DATA1 transaction.
The system impact of this bug is the same regardless of the failure mode
observed. The host core hangs, the ehci_ctrl state machine waits for the
protocol engine to send the completion status for the corrupted
transaction, which never occurs. No indication is sent to the host
controller driver, no register bits change and no interrupts occur.
Eventually the requesting application times out.
Detailed internal behavior:
The EHCI control state machine (ehci_ctrl) in the DMA block is responsible
for parsing the schedules and initiating all transactions. The ehci_ctrl
state machine passes the transaction details to the protocol block by
writing the transaction information in to the TxFIFO. It then asserts
the pe_hst_run_pkt signal to inform the host protocol state machine
(pe_hst_state) that there is a packet in the TxFIFO.
A tag of 0x0 indicates a start of packet with the data providing the
following information:
35:32 Tag
31:30 Reserved
29:23 Endpoint (lowest 4 bits)
22:16 Address
15:10 Reserved
9:8 Endpoint speed
7:6 Endpoint type
5:6 Data Toggle
3:0 PID
The pe_hst_state reads the packet information and constructs the packet
and issues it to the PHY interface.
The ehci_ctrl state machine writes the start transaction information in
to the TxFIFO as 0x03002910c for the OUT packet that had the under run
error. However, it writes 0xC3002910C for the retry of the Out
transaction, which is incorrect.
The pe_hst_state enters a bus timeout state after sending the bad CRC
for the packet that under ran. It then purges any data that was back
filled in to the TxFIFO for the packet that under ran. The pe_hst_state
machine stops purging the TxFIFO when it is empty or if it reads a
location that has a tag of 0x0, indicating a start of packet command.
The pe_hst_state reads 0xC3002910C and discards it as it does not decode
to a start of packet command. It continues to purge the OUT data that
has been pre-buffered for the OUT retry . The pe_hst_state detects the
hst_packet_run signal and attempts to read the PID and address
information from the TxFIFO. This location has packet data and so does
not decode to a valid PID and so falls through to the PE_HST_SOF_LOAD
state where the frame_num_counter is updated. The frame_num_counter
is updated with the data in the TxFIFO. In this case, the data is
incorrect as the ehci_ctrl state machine did not initiate the load.
The hst_pe_state machine detects the SOF request signal and sends an
SOF with the bad frame number. Meanwhile, the ehci_ctrl state machine
waits indefinitely in the run_pkt state waiting for the completion
status from pe_hst_state machine, which will never happen.
The ISO failure case is similar except that there is no retry for ISO.
The ehci_ctrl state machine moves to the next transfer in the periodic
schedule. If the under run occurs on the last entry of the periodic
list then it moves to the Async schedule.
In the case of ISO OUT simulations, the next ISO is a zero byte OUT
and again the start of packet command gets corrupted. The TxFIFO is
empty when the hst_pe_state attempts to read the Address and PID
information as the transaction is a zero byte packet. This results
in the hst_pe_state machine staying in the GET_PID state, which means
that it does not issue any transactions (including SOFs). The device
detects a Suspend condition and reverts to full speed mode and waits
for a Resume or Reset signal.
The EHCI specification allows a Non-DoubleWord (32 bits) offset to
be used as a current offset for Buffer Pointer Page 0 of the qTD.
In Non-DoubleWord aligned cases, the core reads the packet data
from the AHB memory, performs the alignment operation before writing
it in to the TxFIFO as a 32 bit data word. An End Of Packet tag (EOP)
is written to the TxFIFO after all the packet data has been written
in to the TxFIFO. The alignment function is reset to Idle by the EOP
tag. The corruption of the start of packet command arises because the
packet buffer for the OUT transaction that under ran is not aligned
to a DoubleWord, and hence no EOP tag is written to the TxFIFO. The
alignment function is still active when the start packet information
is written in to the TxFIFO for the retry of the bulk packet or for
the next transaction in the case of an under run on an ISO. This
results in the corruption of the start tag and the transaction
information.
Click for waveform showing the command 0x
0000300291 being written in
to the TX FIFO for the Out that under ran.
Click for waveform showing the command 0xC3002910C written to the
TxFIFO instead of 0x
0000300291
Versions affected: Versions 2.10a and previous versions
How discovered: Customer simulation
Workaround:
1- The EHCI specification allows a non-DoubleWord offset to be used
as a current offset for Buffer Pointer Page 0 of the qTD. However,
if a DoubleWord offset is used then this issue does not arise.
2- Use non streaming mode to eliminate under runs.
Resolution:
The fix involves changes to the traffic state machine in the
vusb_hs_dma_traf block. The ehci_ctrl state machine updates the context
information by encoding the transaction results on the
hst_op_context_update signals at the end of a transaction. The signal
hst_op_context_update is added to the traffic state machine, and the
tx_fifo_under_ran_r signal is generated if the transaction results in
an under run error. Click for waveform
The traffic state machine then traverses to the do_eop states if the
tx_fifo_under_ran error is asserted. Thus an EOP tag is written in to
the TxFIFO as shown in this waveform .
The EOP tag resets the align state machine to the Idle state ensuring
that the next command written by the echi_ctrl state machine does not
get corrupted.
File(s) modified:
RTL code fixed: …..
Method of reproducing: This failure cannot be reproduced in the current
test bench.
Date Found: March 2010
Date Fixed: June 2010
Update information:
Added the RTL code fix
Signed-off-by: Peter Chen <peter.chen@freescale.com>
projects / karo-tx-linux.git / commitdiff