Driver API
==========

NOTE: This API is subject to change. It is recommended that you submit your
driver, even if obscure, to the mainline BFGMiner codebase so that it will be
updated when the API changes.

BFGMiner defines 3 different units that drivers can use:
- "Device" is a logical unit used for mining. It is represented by its first
  processor's `struct cgpu_info`. Example: ButterFly Labs MiniRig SC.
- "Processor" is a logical work processing unit. It is represented by a `struct
  cgpu_info` and one or more `struct thr_info`. Example: a single board within
  ButterFly Labs MiniRig SC.
- "Thread" is a sequence of instructions and stack that manages hashing on one
  or more Processors within a single Device. It is represented by a `struct
  thr_info`.

It should be noted that while every Processor has a `struct thr_info`, this may
not represent the same Thread which is managing hashing on the Processor.
Instead, this `struct thr_info` is only used to store status information needed
for the Processor, and is maintained by the managing Thread in addition to its
own `struct thr_info`. New drivers are encouraged to use an asynchronous model
to manage as many Processors as possible within a single Thread.

struct device_api basics
------------------------

Every driver defines a `struct device_api`. The `dname` field contains a
short name of the driver. This should be the same name used in the source file:
driver-foobar.c defines `dname` "foobar". The `name` field contains a three-
letter abbreviation for the device, used in the representation of devices. For
example, `dname` "FOO" would result in devices represented as "FOO 0", "FOO 1",
etc and processors represented as "FOO 0a", "FOO 0b", etc.

Drivers must define a function `api_detect`, which is run at startup to detect
devices. For each device (note: NOT each processor), it should allocate a
`struct cgpu_info`, set some basic parameters on it, and call the `add_cgpu`
function with it as an argument. Various values you can initialize are:
	.api         This MUST be set to your driver's `struct driver_api`!
	.deven       Should be set to DEV_ENABLED
	.procs       Number of Processors for this device
	.threads     Number of threads your device needs - should be either a
	             multiple of .procs (threads will be allocated to each
	             Processor), or one (a single thread will be allocated only to
	             the Device, to manage all Processors)
	.name        Null-terminated name of the device itself
`api_detect` should return the total number of devices created. It should leave
the device in an unused state, as the user may opt to delete it outright.

Threads
-------

The first interaction BFGMiner will have with a device is by calling the
driver's `thread_prepare` function for each Thread. This occurs while BFGMiner
is still in a single-threaded state, before any Threads have actually started
running independently. It should do only the minimal initialization necessary
to proceed, and return true iff successful.

Once all the Threads are setup, BFGMiner starts them off by calling the
`thread_init` function. This should do all initialization that can occur in
parallel with other Threads.

The driver should specify a `minerloop` to use. For the purposes of this
document, it is assumed you will be using `minerloop_async`. Please note that
the default is currently `minerloop_scanhash`, and much of the documentation
here will NOT work with this `minerloop`.

Processors
----------

Processors work with `struct work` objects, which each represent a block header
to find a solution for. Before your driver sees a `struct work`, it will be
passed to the function `prepare_work` with pointers to the Processor `struct
thr_info` and the `struct work` as arguments. Most drivers do not need to do
anything at this stage, so feel free to omit the `prepare_work` function.

For each job, the `job_prepare` function is called in advance, with three
arguments: Processor `struct thr_info *`, `struct work *`, and a `uint64_t`
limiting how many nonces to check (starting from `work->blk.nonce`). Unless you
implement a `can_limit_work` function, you will always receive a full nonce
range from 0 to 0xffffffff. `job_prepare` increments `work->blk.nonce` to the
last nonce the processor will be attempting and returns true when successful.
Please note this will be called while the previous job is still executing.

When it is time to actually start the new job, the `job_start` function will be
called. This is given the Processor `struct thr_info *` as its only argument,
and should start the job most recently prepared with `job_prepare`. Note that
it is possible for `job_prepare` to be called for a job that never starts
(another `job_prepare` may be executed to override the previous one instead).
`job_start` must call `mt_job_transition` as soon as the actual switchover to
the new job takes place, and must call `job_start_complete` when successful;
in case of a failure, it should call `job_start_abort` instead. `job_start`
must set `thr->tv_morework` to the time the device expects to need its next
work item. It is generally advisable to set this a bit early to ensure any
delays do not make it late. `job_start` is expected to always succeed and does
not have a return value.

Immediately before `job_start` is called to change from one job to the next,
`job_get_results` will be called to fetch any volatile results from the
previous job. It is provided the Processor's `struct thr_info *` and the
currently executing job's `struct work *`. It should ONLY fetch the raw data
for the results, and not spend any time processing or submitting it. If
`job_get_results` is defined for your driver, it must (directly or indirectly)
ensure `job_results_fetched` is called when complete (including the case of
failure). After the new job has been started, your driver's
`job_process_results` function will be called to complete the submission of
these results with the same arguments, plus a bool to tell you whether the
processor is being stopped. If it is, your driver must call `mt_disable_start`
when it has successfully stopped hashing.

Drivers may define a `poll` function. If this is defined, `thr->tv_poll` must
always be set to a valid time to next execute it, for each Processor.

Whenever a solution is found (at any point), the function `submit_nonce` should
be called, passing the Processor `struct thr_info *`, `struct work *`, and
nonce as arguments. If the solution is invalid (any of the final 32 bits of the
hash are nonzero), it will be recorded as a hardware error and your driver's
`hw_error` function (if one is defined) will be called.

As often as results are processed, your driver should call the `hashes_done`
function with a number of arguments: Processor `struct thr_info *`, count of
hashes completed (including calls to `submit_nonce`), a `struct timeval *`
that tells how long it took to find these hashes (usually time since the last
call to `hashes_done`, and a `uint32_t *` which should usually be NULL.
