media/cec/cec-pin-error-inj.rst

1 .. SPDX-License-Identifier: GFDL-1.1-no-invariants-or-later
9 has low-level support for the CEC bus. Most hardware today will have
10 high-level CEC support where the hardware deals with driving the CEC bus,
15 What makes doing this so interesting is that since we have full control
19 Currently only the cec-gpio driver (when the CEC line is directly
20 connected to a pull-up GPIO line) and the AllWinner A10/A20 drm driver
25 now an ``error-inj`` file.
32 With ``cat error-inj`` you can see both the possible commands and the current
35 	$ cat /sys/kernel/debug/cec/cec0/error-inj
38 	#   rx-clear       clear all rx error injections
39 	#   tx-clear       clear all tx error injections
41 	#   <op> rx-clear  clear all rx error injections for <op>
42 	#   <op> tx-clear  clear all tx error injections for <op>
45 	#   <op>[,<mode>] rx-nack              NACK the message instead of sending an ACK
46 	#   <op>[,<mode>] rx-low-drive <bit>   force a low-drive condition at this bit position
47 	#   <op>[,<mode>] rx-add-byte          add a spurious byte to the received CEC message
48 	#   <op>[,<mode>] rx-remove-byte       remove the last byte from the received CEC message
49 	#    any[,<mode>] rx-arb-lost [<poll>] generate a POLL message to trigger an arbitration lost
52 	#   tx-ignore-nack-until-eom           ignore early NACKs until EOM
53 	#   tx-custom-low-usecs <usecs>        define the 'low' time for the custom pulse
54 	#   tx-custom-high-usecs <usecs>       define the 'high' time for the custom pulse
55 	#   tx-custom-pulse                    transmit the custom pulse once the bus is idle
58 	#   <op>[,<mode>] tx-no-eom            don't set the EOM bit
59 	#   <op>[,<mode>] tx-early-eom         set the EOM bit one byte too soon
60 	#   <op>[,<mode>] tx-add-bytes <num>   append <num> (1-255) spurious bytes to the message
61 	#   <op>[,<mode>] tx-remove-byte       drop the last byte from the message
62 	#   <op>[,<mode>] tx-short-bit <bit>   make this bit shorter than allowed
63 	#   <op>[,<mode>] tx-long-bit <bit>    make this bit longer than allowed
64 	#   <op>[,<mode>] tx-custom-bit <bit>  send the custom pulse instead of this bit
65 	#   <op>[,<mode>] tx-short-start       send a start pulse that's too short
66 	#   <op>[,<mode>] tx-long-start        send a start pulse that's too long
67 	#   <op>[,<mode>] tx-custom-start      send the custom pulse instead of the start pulse
68 	#   <op>[,<mode>] tx-last-bit <bit>    stop sending after this bit
69 	#   <op>[,<mode>] tx-low-drive <bit>   force a low-drive condition at this bit position
71 	# <op>       CEC message opcode (0-255) or 'any'
73 	# <bit>      CEC message bit (0-159)
74 	#            10 bits per 'byte': bits 0-7: data, bit 8: EOM, bit 9: ACK
75 	# <poll>     CEC poll message used to test arbitration lost (0x00-0xff, default 0x0f)
76 	# <usecs>    microseconds (0-10000000, default 1000)
80 You can write error injection commands to ``error-inj`` using
81 ``echo 'cmd' >error-inj`` or ``cat cmd.txt >error-inj``. The ``cat error-inj``
83 and use it as an input to ``error-inj`` later.
86 ------------
95 to create custom pulses on the CEC bus.
105 So '``any rx-nack``' will NACK the next received CEC message,
106 '``any,always rx-nack``' will NACK all received CEC messages and
107 '``0x82,toggle rx-nack``' will only NACK if an Active Source message was
111 is cleared automatically, so ``once`` is a one-time deal.
113 All combinations of ``<op>`` and error injection commands can co-exist. So
116 	0x9e tx-add-bytes 1
117 	0x9e tx-early-eom
118 	0x9f tx-add-bytes 2
119 	any rx-nack
126 	0x9e tx-add-bytes 1
127 	0x9e tx-add-bytes 2
132 ----------------------
137 ``rx-clear``
140 ``tx-clear``
146 ``<op> rx-clear``
149 ``<op> tx-clear``
153 ----------------
155 ``<op>[,<mode>] rx-nack``
160 ``<op>[,<mode>] rx-low-drive <bit>``
169 ``<op>[,<mode>] rx-add-byte``
172     the high-level protocol since spurious bytes should be ignored.
174 ``<op>[,<mode>] rx-remove-byte``
176     was at least 2 bytes long. This is useful to test the high-level
179 ``<op>[,<mode>] rx-arb-lost <poll>``
197 -----------------
199 ``tx-ignore-nack-until-eom``
202     specification also allows that the full message is transmitted and only
210 ``<op>[,<mode>] tx-no-eom``
212     (End-Of-Message) bit set. With this command the transmit will just stop
214     handles this case. Normally receivers have a time-out after which
217 ``<op>[,<mode>] tx-early-eom``
219     of two bytes or more. The EOM bit will be set for the second-to-last byte
225 ``<op>[,<mode>] tx-add-bytes <num>``
226     Append ``<num>`` (1-255) spurious bytes to the message. The extra bytes
229     the full message received by the remote CEC adapter is
236 ``<op>[,<mode>] tx-remove-byte``
240 ``<op>[,<mode>] tx-short-bit <bit>``
253     sees a too-short 0 bit.
255 ``<op>[,<mode>] tx-long-bit <bit>``
271     sees a too-long 0 bit.
273 ``<op>[,<mode>] tx-short-start``
280 ``<op>[,<mode>] tx-long-start``
292 ``<op>[,<mode>] tx-last-bit <bit>``
299 ``<op>[,<mode>] tx-low-drive <bit>``
304     positions 0-3 the receiver can interpret this as an Arbitration Lost
307 Custom Pulses
308 -------------
310 ``tx-custom-low-usecs <usecs>``
311     This defines the duration in microseconds that the custom pulse pulls
314 ``tx-custom-high-usecs <usecs>``
315     This defines the duration in microseconds that the custom pulse keeps the
317     The default is 1000 microseconds. The total period of the custom pulse is
318     ``tx-custom-low-usecs + tx-custom-high-usecs``.
320 ``<op>[,<mode>] tx-custom-bit <bit>``
321     Send the custom bit instead of a regular data bit. The bit position cannot
325 ``<op>[,<mode>] tx-custom-start``
326     Send the custom bit instead of a regular start bit.
328 ``tx-custom-pulse``
329     Transmit a single custom pulse as soon as the CEC bus is idle.