Hi
On Tue, Jul 16, 2013 at 12:32 PM, Benjamin Tissoires
<benjamin.tissoires@xxxxxxxxx> wrote:
> Hi David,
>
> On Mon, Jul 15, 2013 at 7:10 PM, David Herrmann <dh.herrmann@xxxxxxxxx>
> wrote:
>> hid-transport.txt describes the transport driver layout which is required
>> by HID-core to work correctly. HID-core supports many different transport
>> drivers and new drivers can be added for any kind of I/O system.
>>
>> The current layout doesn't really differentiate between intr and ctrl
>> channels, which confuses some hid-drivers and may break devices. HIDP,
>> USBHID and I2DHID all implement different semantics for each callback, so
>
> typo: I2CHID
Fixed, thx!
>> our device drivers aren't really transport-driver-agnostic.
>>
>> To solve that, hid-transport.txt describes the layout of transport drivers
>> that is required by HID core. Furthermore, it introduces some new
>> callbacks which replace the current hid_get_raw_report() and
>> hid_output_raw_report() hooks. These will be implemented in follow-up
>> patches.
>>
>> Signed-off-by: David Herrmann <dh.herrmann@xxxxxxxxx>
>> ---
>> Documentation/hid/hid-transport.txt | 299 ++++++++++++++++++++++++++++++++++++
>> 1 file changed, 299 insertions(+)
>> create mode 100644 Documentation/hid/hid-transport.txt
>>
>> diff --git a/Documentation/hid/hid-transport.txt b/Documentation/hid/hid-transport.txt
>> new file mode 100644
>> index 0000000..034f11d
>> --- /dev/null
>> +++ b/Documentation/hid/hid-transport.txt
>> @@ -0,0 +1,299 @@
>> + HID I/O Transport Drivers
>> + ===========================
>> +
>> +The HID subsystem is independent of the underlying transport driver. Initially,
>> +only USB was supported, but other specifications adopted the HID design and
>> +provided new transport drivers. The kernel includes at least support for USB,
>> +Bluetooth, i2c and user-space I/O drivers.
>
> IIRC, we should put I2C in capital letters.
Yepp, fixed.
>> +
>> +1) HID Bus
>> +==========
>> +
>> +The HID subsystem is designed as a bus. Any I/O subsystem may provide HID
>> +devices and register them with the HID bus. HID core then loads generic device
>> +drivers on top of it. The transport drivers are responsible of raw data
>> +transport and device setup/management. HID core is responsible of
>> +report-parsing, report interpretation and the user-space API. Device specifics
>> +and quirks are also handled by HID core and the HID device drivers.
>
> Hmm, the quirks part is not exactly what is currently implemented.
> Usbhid (Transport Driver) set and use quirks while you say here that
> they are handled by hid-core.
>
> I personally prefer the way it is documented here (quirks handled in
> hid-core) so HIDP, i2c-hid and uhid will benefit from the dynamic quirks
> already implemented in usbhid. But that will require another patch :)
I actually meant things like wrong report-descriptors or special
device drivers. Of course, there are also quirks that apply to the
transport driver layer. I will rephrase that.
>> +
>> + +-----------+ +-----------+ +-----------+ +-----------+
>> + | Device #1 | | Device #i | | Device #j | | Device #k |
>> + +-----------+ +-----------+ +-----------+ +-----------+
>> + \\ // \\ //
>> + +------------+ +------------+
>> + | I/O Driver | | I/O Driver |
>> + +------------+ +------------+
>> + || ||
>> + +------------------+ +------------------+
>> + | Transport Driver | | Transport Driver |
>> + +------------------+ +------------------+
>> + \___ ___/
>> + \ /
>> + +----------------+
>> + | HID Core |
>> + +----------------+
>> + / | | \
>> + / | | \
>> + ____________/ | | \_________________
>> + / | | \
>> + / | | \
>> + +----------------+ +-----------+ +------------------+ +------------------+
>> + | Generic Driver | | MT Driver | | Custom Driver #1 | | Custom Driver #2 |
>> + +----------------+ +-----------+ +------------------+ +------------------+
>> +
>> +Example Drivers:
>> + I/O: USB, I2C, Bluetooth-l2cap
>> + Transport: USB-HID, I2C-HID, BT-HIDP
>> +
>> +Normally, a transport driver is specific for a given I/O driver. But the HID
>> +design also allows transport drivers to work with different I/O systems at the
>> +same time.
>
> I do not follow you here. Which transport driver you have in mind?
There is none such driver, I just wanted to point out that HID-core
doesn't care. Turns out to be more confusing than helping so I guess I
will just drop it.
>> +
>> +Everything below "HID Core" is simplified in this graph as it is only of
>> +interest to HID device drivers. Transport drivers do not need to know the
>> +specifics.
>> +
>> +1.1) Device Setup
>> +-----------------
>> +
>> +I/O drivers normally provide hotplug detection or device enumeration APIs to the
>> +transport drivers. Transport drivers use this to find any suitable HID device.
>> +They allocate HID device objects and register them with HID core. Transport
>> +drivers are not required to register themselves with HID core. HID core is never
>> +aware of which transport drivers are available and is not interested in it. It
>> +is only interested in devices.
>> +
>> +Transport drivers attach a constant "struct hid_ll_driver" object with each
>> +device. Once a device is registered with HID core, the callbacks provided via
>> +this struct are used by HID core to communicate with the device.
>> +
>> +Transport drivers are responsible of detecting device failures and unplugging.
>> +HID core will operate an device as long as it is registered regardless of any
>
> typo: ^^ "a"
Fixed.
>> +device failures. Once transport drivers detect unplug or failure events, they
>> +must unregister the device from HID core and HID core will stop using the
>> +provided callbacks.
>> +
>> +1.2) Transport Driver Requirements
>> +----------------------------------
>> +
>> +HID core requires transport drivers to follow a given design. A Transport
>> +drivers must provide two bi-directional I/O channels to each HID device. These
>> +channels might be multiplexed on a single physical channel, though.
>> +
>> + - Interrupt Channel (intr): The intr channel is used for asynchronous data
>> + reports. No management commands or data acknowledgements are sent on this
>> + channel. Any unrequested incoming or outgoing data report must be sent on
>> + this channel and is never acknowledged by the remote side. Devices usually
>> + send their input events on this channel. Outgoing events are normally
>> + not send via intr, except if high throughput is required.
>> + - Control Channel (ctrl): The ctrl channel is used for synchronous requests and
>> + device management. Unrequested data input events must not be sent on this
>> + channel and are normally ignored. Instead, devices only send management
>> + events or answers to host requests on this channel.
>> + Outgoing reports are usually sent on the ctrl channel via synchronous
>> + SET_REPORT requests.
>
> This is not entirely true for USB and I2C:
> - for USB, OUTPUT reports can also be sent through a direct write on an URB.
> - for I2C, the notion of intr vs ctrl is slightly different, but it
> remains roughly the same. Let me detail it so that you can make your idea:
> The HID descriptors declares three I2C registers:
> * the "Input" register: this one correspond to the intr you are
> describing. The difference is that this register is only used from the
> communication from the device to the host (no outputs here). The big
> interest in this register is that the communication is device initiated
> thanks to an external line triggered by the device (in I2C, the
> communication is only master (host) initiated).
> * the "Command" register: this one corresponds to the ctrl channel.
> This channel/register is host initiated too (like on the USB side), and
> there is a slight head over due to the HID protocol regarding sending
> output events.
> * the "Output" register: this one corresponds to the URBs described in
> USB. Every communication coming from the host on this channel is
> considered as an OUTPUT report, reducing the HID protocol over head.
>
> The HID/I2C also declares a forth register (the "data") register which
> is used by the HID protocol while using the "Command" register.
>
>
> To sum up, I think the differences between the channels are:
> - Interrupt Channel (intr): asynchronous, device initiated, no
> acknowledgements (beside the fact that data has been read), read only.
> - Control Channel (ctrl): synchronous, host initiated, acknowledged
> (because synchronous), read/write
> - Output Channel (out): synchronous, host initiated, acknowledged
> (because synchronous), write only
I intetionally described the channels as "bi-directional". So you
actually describe the same scenario, but from a different view-point
(mine obviously is HIDP). So if you consider the OUT channel to be the
same as writing on INTR, you will get the same scenario. I am not
entirely sure which is better, but I can change it to your description
if it helps?
Regarding asynchronous vs. synchronous: I actually don't care how the
I/O layer implements it. In this document, "asynchronous" means that I
don't care for any acknowledgements. "synchronous" means, the remote
device acknowledges the receival. Obviously, if an I/O system always
acknowledges a SENT, then a transport driver can implement
asynchronous transports as synchronous transports (which might mean
having a separate buffer like USBHID does). But HID-core does not
care.
Same situation if synchronous is not supported. HID-core assumes it is
synchronous so the transport layer can simply fake an acknowledgement.
However, this means that the transport-layer might have to take care
of retransmissions if an asynchronous transport fails (which L2CAP in
Bluetooth-Core does tranparently for HIDP).
I will try to be more verbose, but I intentionally posted all the
callbacks below which should explain that "asynchronous" means it can
be called in atomic-context and "synchronous" means it is allowed to
sleep and wait for acknowledgement (speaking of code).
Thanks a lot for the I2C explanation, I think I understand it now and
it does resemble USBHID and HIDP very much!
> Then, the usbhid transport layer makes the ctrl and out channels
> asynchronous...
>
>> +
>> +Communication between devices and HID core is mostly done via HID reports. A
>> +report can be of one of three types:
>> +
>> + - INPUT Report: Input reports provide data from device to host. This
>> + data may include button events, axis events, battery status or more. This
>> + data is generated by the device and sent to the host without requiring
>
> _with_ or without requiring explicit requests.
> On I2C, the command GET_REPORT is even mandatory (which does not seems
> to be the case for USB, given the amount of QUIRK_NO_INIT_REPORT we have.)
You're right, they can be sent synchronously via GET_REPORT, too.
But I don't know what you mean that GET_REPORT is mandatory? I thought
an I2C device sends the data and fires an IRQ? Or is, upon interrupt
receival, the host required to send a GET_REPORT to receive the
pending input-event? I sadly have no idea how I2C works, but if it is
_only_ host initiated, then this makes sense. Just want to go sure.
Anyway, even if I2C requires an explicit GET_REPORT, this doesn't
conflict with this description. It's an implementation detail of I2C
and HID-core doesn't care if input events require a GET_REPORT.
>> + explicit requests. Devices can choose to send data continously or only on
>
> My spell checker gives me a typo on: "continuously"
Whoops, right.
>> + change.
>> + - OUTPUT Report: Output reports change device states. They are sent from host
>> + to device and may include LED requests, rumble requests or more. Output
>> + reports are never sent from device to host, except if explicitly requested.
>
> In this case, I think it would be better to say that Output reports are
> never sent from device to host, but the host can _retrieve_ its current
> state.
Yepp, makes sense.
>> + Hosts may choose to send output reports either continously or only on change.
>
> My spell checker gives me a typo on: "continuously"
Fixed.
>> + - FEATURE Report: Feature reports can be anything that doesn't belong into the
>> + other two categories. Some of them are generic and defined by the HID spec,
>> + but most of them are used as custom device extensions. For instance, they may
>> + provide battery status information.
>
> I disagree. FEATURE are specific reports which are read/write, and not
> spontaneously emitted by the device. For instance, this allows the host
> to change the current mode of the device (mouse emulation or multitouch
> in the case I know most), or to set constants in the device (max
> reported touches in my case, but this can be hardware macros for
> keyboards, or something else).
This is actually what I meant. But I agree, it isn't really clear from
my description.
>> + Feature reports are never sent without requests. A host must explicitly
>> + request a device to set or send a feature report. This also means, feature
>
> I would prefer a "host must explicitly request a device to set or
> _retrieve_ a feature report".
Yepp, fixed.
>> + reports are never sent on the intr channel as this channel is asynchronous.
>> +
>> +INPUT and OUTPUT reports can be sent as pure data reports on the intr channel.
>
> In my mind, OUTPUT reports are not sent through the intr channel
> (because write only), but you already get my point I think :)
Yeah, as explained above I merged INTR and OUTPUT into a bi-directional channel.
>> +For INPUT reports this is the usual operational mode. But for OUTPUT reports,
>> +this is rarely done as OUTPUT reports are normally quite rare. But devices are
>> +free to make excessive use of asynchronous OUTPUT reports (for instance, custom
>> +HID audio speakers make great use of it).
>
> Ok, did not know about it.
>
>> +
>> +Raw reports must not be sent on the ctrl channel, though. Instead, the ctrl
>> +channel provides synchronous GET/SET_REPORT requests.
>> +
>> + - GET_REPORT: A GET_REPORT request has a report ID as payload and is sent
>> + from host to device. The device must answer with a data report for the
>> + requested report ID on the ctrl channel as a synchronous acknowledgement.
>
> Beware that the report ID is not mandatory in case the HID report
> descriptors declares only 1 report without report ID. But I'm fine with
> it anyway (it's understandable that way).
Ugh, I am not entirely sure but afaik HIDP doesn't support implicit
IDs. Could you tell me whether I2C supports it?
A report-descriptor can skip report IDs if there is only a single
report? Didn't know that, but we definitely need to document it.
>> + Only one GET_REPORT request can be pending for each device. This restriction
>> + is enforced by HID core as several transport drivers don't allow multiple
>> + simultaneous GET_REPORT requests.
>> + Note that data reports which are sent as answer to a GET_REPORT request are
>> + not handled as generic device events. That is, if a device does not operate
>> + in continuous data reporting mode, an answer to GET_REPORT does not replace
>> + the raw data report on the intr channel on state change.
>> + GET_REPORT is only used by custom HID device drivers to query device state.
>> + Normally, HID core caches any device state so this request is not necessary
>> + on devices that follow the HID specs.
>
> FYI, HID/I2C spec says: "GET_REPORT is often used by applications on
> startup to retrieve the ``current state'' of the device rather than
> waiting for the device to generate the next input/feature report".
Yeah, for startup this makes sense. I will add a short note.
> And as under Linux applications do not talk directly to the hid devices,
> I fully concurs to your point.
>
>> + GET_REPORT requests can be sent for any of the 3 report types and shall
>> + return the current report state of the device.
>
> The HID/I2C spec explicitly says: "the DEVICE shall ignore a GET_REPORT
> requests with the REPORT TYPE set to Output, as it is not used in this
> specification." So under i2c, we can send GET_REPORT with OUTPUT, but we
> will not get anything from the device (this is why it is forbidden by
> the transport driver).
Heh, didn't know that, either. It's fine if I2C ignores it. However,
I'd like to avoid forbidding it. There can be devices which use this
(companies to crazy things..) and I cannot see a reason to forbid it
in HID core. The transport drivers are free to adhere to their
specifications, though. I guess that's fine?
>> + - SET_REPORT: A SET_REPORT request has a report ID plus data as payload. It is
>> + sent from host to device and a device must update it's current report state
>> + according to the given data. Any of the 3 report types can be used.
>
> The HID/I2C spec explicitly says: "the DEVICE might choose to ignore
> input SET_REPORT requests as meaningless."...
Same as above I think. But thanks for the clarification! I guess I
will add a note that it is discouraged and devices are not supposed to
handle it. This should clear all doubts.
>> + A device must answer with a synchronous acknowledgement. However, HID core
>> + does not require transport drivers to forward this acknowledgement to HID
>> + core.
>> + Same as for GET_REPORT, only one SET_REPORT can be pending at a time. This
>> + restriction is enforced by HID core as some transport drivers do not support
>> + multiple synchronous SET_REPORT requests.
>> +
>> +Other ctrl-channel requests are supported by USB-HID but are not available
>> +(or deprecated) in most other transport level specifications:
>> +
>> + - GET/SET_IDLE: Only used by USB-HID. Do not implement!
>> + - GET/SET_PROTOCOL: Not used by HID core. Do not implement!
>
> The I2C declares also:
> - RESET: mandatory (reset the device at any time)
> - SET_POWER: mandatory on the device side (request from host to device
> to indicate preferred power setting).
Are they hooked up to HID-core? I'd like to avoid any commands which
are handled transparently in the transport driver (like
suspend/resume). However, SET_POWER sounds related to ->power()
callback. I will look through it again and include it in the next
revision if it is hooked up.
>> +
>> +2) HID API
>> +==========
>> +
>> +2.1) Initialization
>> +-------------------
>> +
>> +Transport drivers normally use the following procedure to register a new device
>> +with HID core:
>> +
>> + struct hid_device *hid;
>> + int ret;
>> +
>> + hid = hid_allocate_device();
>> + if (IS_ERR(hid)) {
>> + ret = PTR_ERR(hid);
>> + goto err_<...>;
>> + }
>> +
>> + strlcpy(hid->name, <device-name-src>, 127);
>> + strlcpy(hid->phys, <device-phys-src>, 63);
>> + strlcpy(hid->uniq, <device-uniq-src>, 63);
>> +
>> + hid->ll_driver = &custom_ll_driver;
>> + hid->bus = <device-bus>;
>> + hid->vendor = <device-vendor>;
>> + hid->product = <device-product>;
>> + hid->version = <device-version>;
>> + hid->country = <device-country>;
>
> FYI, HID/I2C does not define any device-country field (I guess it will
> come in a later release...)
Right, I think BT also sets it to 0 in bluez. I will add a note that
"0" is the default value.
>> + hid->dev.parent = <pointer-to-parent-device>;
>
> FYI, I have started implementing a devm API for HID (in the same way the
> input devm API is implemented), and dev.parent should not be overwritten.
Cool! I will adjust the document once it is merged.
> Anyway the two last comments are not requesting any changes in the document.
>
>> + hid->driver_data = <transport-driver-data-field>;
>> +
>> + ret = hid_add_device(hid);
>> + if (ret)
>> + goto err_<...>;
>> +
>> +Once hid_add_device() is entered, HID core might use the callbacks provided in
>> +"custom_ll_driver". To unregister a device, use:
> ^^^^
> Maybe introduce a new paragraph (otherwise, it looks like
> hid_destroy_device is called from HID core).
Indeed, will do that.
>> +
>> + hid_destroy_device(hid);
>> +
>> +Once hid_destroy_device() returns, HID core will no longer make use of any
>> +driver callbacks.
>> +
>> +2.2) hid_ll_driver operations
>> +-----------------------------
>> +
>> +The available HID callbacks are:
>> + - int (*start) (struct hid_device *hdev)
>> + Called from HID device drivers once they want to use the device. Transport
>> + drivers can choose to setup their device in this callback. However, normally
>> + devices are already set up before transport drivers register them to HID core
>> + so this is mostly only used by USB-HID.
>> +
>> + - void (*stop) (struct hid_device *hdev)
>> + Called from HID device drivers once they are done with a device. Transport
>> + drivers can free any buffers and deinitialize the device. But note that
>> + ->start() might be called again if another HID device driver is loaded on the
>> + device.
>> + Transport drivers are free to ignore it and deinitialize devices after they
>> + destroyed them via hid_destroy_device().
>> +
>> + - int (*open) (struct hid_device *hdev)
>> + Called from HID device drivers once they are interested in data reports.
>> + Usually, while user-space didn't open any input API/etc., device drivers are
>> + not interested in device data and transport drivers can put devices asleep.
>> + However, once ->open() is called, transport drivers must be ready for I/O.
>> + ->open() calls are never nested. So in between two ->open() calls there must
>> + be a call to ->close().
>
> This is not true in either USB or I2C. And I guess with every BT or UHID
> devices. ->open() and ->close() are called upon open/close of the input
> node (or hidraw, or hiddev). So If two clients are opening the same
> input node, there will be two calls to ->open() without any call to
> ->close() in between.
>
> I guess you mixed up this part with the ->start() ->stop() :)
I got confused, indeed. input-core only calls ->open() on first-open,
but there might be multiple input devices. So you're right. I will fix
this. Thanks for catching it!
>> +
>> + - void (*close) (struct hid_device *hdev)
>> + Called from HID device drivers after ->open() was called but they are no
>> + longer interested in device reports. (Usually if user-space closed any input
>> + devices of the driver).
>> + Transport drivers can put devices asleep and terminate any I/O. However,
>> + ->start() may be called again if the device driver is interested in input
>> + reports again.
>> +
>> + - int (*parse) (struct hid_device *hdev)
>> + Called once during device setup after ->start() has been called. Transport
>> + drivers must read the HID report-descriptor from the device and tell HID core
>> + about it via hid_parse_report().
>> +
>> + - int (*power) (struct hid_device *hdev, int level)
>> + Called by HID core to give PM hints to transport drivers. Usually this is
>> + analogical to the ->open() and ->close() hints and redundant.
>> +
>> + - void (*request) (struct hid_device *hdev, struct hid_report *report,
>> + int reqtype)
>> + Send an HID request on the ctrl channel. "report" contains the report that
>> + should be sent and "reqtype" the request type. Request-type can be
>> + HID_REQ_SET_REPORT or HID_REQ_GET_REPORT.
>> + This callback is optional. If not provided, HID core will assemble a raw
>> + report following the HID specs and send it via the ->raw_request() callback.
>> + The transport driver is free to implement this asynchronously.
>> +
>> + - int (*wait) (struct hid_device *hdev)
>> + Used by HID core before calling ->request() again. A transport driver can use
>> + it to wait for any pending requests to complete if only one request is
>> + allowed at a time.
>> +
>> + - int (*raw_request) (struct hid_device *hdev, unsigned char reportnum,
>> + __u8 *buf, size_t count, unsigned char rtype,
>> + int reqtype)
>> + Same as ->request() but provides the report as raw buffer. This request shall
>> + be synchronous. A transport driver must not use ->wait() to complete such
>> + requests.
>
> 2 questions/remarks here:
> - is raw_request() meant to replace ->hid_output_raw_report() and
> ->hid_get_raw_report()?
Both. raw_request() with HID_REQ_GET_REPORT replaces
hid_get_raw_report() and with HID_REQ_SET_REPORT it replaces
hid_output_raw_report().
However, at least HIDP implements hid_output_raw_report() with
HID_OUTPUT_REPORT as raw output report instead of SET_REPORT. For
this, "output_report()" below can be used.
> - reportnum declared as an unsigned will be problematic regarding the
> rare devices not having any report ID in their report descriptors.
I thought reportnum 0 is an invalid ID? I will check again and change
to signed if needed. Thanks!
>> +
>> + - int (*output_report) (struct hid_device *hdev, __u8 *buf, size_t len)
>> + Send raw output report via intr channel. Used by some HID device drivers
>> + which require high throughput for outgoing requests on the intr channel. This
>> + must not cause SET_REPORT calls! This must be implemented as asynchronous
>> + output report on the intr channel!
>
> For me, there is something wrong here. The name infers that we are
> trying to send an output_report directly (so through the USB URB or
> through the output i2c register), but you are implementing it through
> the intr channel... :-S
Again, "write on INTR" is OUTPUT channel for me. So I guess with the
explanation above we are fine here?
>> +
>> + - int (*hidinput_input_event) (struct input_dev *idev, unsigned int type,
>> + unsigned int code, int value)
>> + Obsolete callback used by logitech converters. It is called when userspace
>> + writes input events to the input device (eg., EV_LED). A driver can use this
>> + callback to convert it into an output report and send it to the device. If
>> + this callback is not provided, HID core will use ->request() or
>> + ->raw_request() respectively.
>
> I bet there will be a way to make this work with logitech devices too
> (if we implement a proper ->hid_output_raw_report() in each paired devices).
Yeah, I thought so, but I have no idea what the logitech-dj driver
does. I guess we can drop this once we have no more users, but I
wanted to avoid pushing to hard on it.
>> +
>> + - int (*idle) (struct hid_device *hdev, int report, int idle, int reqtype)
>> + Perform SET/GET_IDLE request. Only used by USB-HID, do not implement!
>> +
>> +2.3) Data Path
>> +--------------
>> +
>> +Transport drivers are responsible of reading data from I/O devices. They must
>> +handle any state-tracking themselves. HID core does not implement protocol
>
> I don't get the "state-tracking" here. The reports states should be
> handled by core, and I do not see the other states (or you meant PM
> states?).
Ugh, I meant I/O-related state-tracking (or PM). I will rephrase that.
>> +handshakes or other management commands which can be required by the given HID
>> +transport specification.
>> +
>> +Every raw data packet read from a device must be fed into HID core via
>> +hid_input_report(). You must specify the channel-type (intr or ctrl) and report
>> +type (input/output/feature). Under normal conditions, only input reports are
>> +provided via this API.
>> +
>> +Responses to GET_REPORT requests via ->request() must also be provided via this
>> +API. Responses to ->raw_request() are synchronous and must be intercepted by the
>> +transport driver and not passed to hid_input_report().
>> +Acknowledgements to SET_REPORT requests are not of interest to HID core.
>> +
>> +----------------------------------------------------
>> +Written 2013, David Herrmann <dh.herrmann@xxxxxxxxx>
>> --
>> 1.8.3.2
>>
>
> done!
> Many thanks for this David. It was very interesting and detailed. It
> will make a great documentation.
Thanks a lot for reviewing. I will fix the remaining issues and with
the "write-on-INTR is OUTPUT" I guess we are on the same page (except
for minor issues)?
Cheers
David
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