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Rewrote the .template/.substitution expansion

Simon Rose authored 2 years ago

This is necessary for the following reason: the previous mechanism used an
eval/call combination that required SUBS and TMPS to be exported on a previous
pass through. This allowed us to use `vpath` for each specific file in order
to locate the correct source files.

In order to avoid that, we add two new ingredients:
* `VPATH` instead of `vpath`, since it allows us to have variables
  that are expanded later
* `.SECONDEXPANSION`, which allows a target (`db_internal`, in this case) to
  perform a second variable expansion at the _end_ of the pass through.

All of this is necessary because the typical module makefile looks like:
```
include driver.makefile

SUBS += ...
```
i.e. `SUBS` and `TMPS` are defined _after_ the inclusion of driver.makefile. If
we don't want to force a re-write of every single module makefile, we needed
to do some of the above changes.

96d2346d

96d2346d 2 years ago

Name	Last commit	Last update
configure
require-ess
tests
tools
.clang-format
.flake8
.gitattributes
.gitignore
.gitlab-ci.yml
.pre-commit-config.yaml
CHANGELOG.md
Makefile
README.md
require.Makefile

e3-require

The e3 version of require based on the PSI version of require. There are significant diferences between the two modules, significant enough that it is not proper to call it a fork any longer.

At its heart, require performs:

Dynamic loading of EPICS modules and rudimentary dependency resolution
Loading of IOCs using a custom startup script calling softIocPVA
Building of EPICS modules into standardized e3 packages

For more documentation on this, please see e3.pages.

Structural differences between PSI require and ESS require

The main differences between the two is that ESS require includes a number of configuration files defining special build targets for EPICS modules. For example, the following targets are defined.

make build - Runs the custom build process defined in require.
make vars - Displays a number of custom build variables e.g. install locations, etc.
make debug - Runs a debug build process, displaying information about the current build
make cellinstall - Installs the module in a local directory, e.g. for testing purposes

For more special rules, look at the files in [configure/modules].

The main parts that we have taken from PSI require are require.c and driver.makefile, which respectively load modules dynamically at run-time, and which run the custom build process. However, both of these have been modified significantly for the purposes of e3.

Furthermore, we have added the custom startup script iocsh which sets up the IOC's environment before running softIocPVA from EPICS base.

Building `require`

In order to build require, you must first have EPICS base installed. After that, you must configure CONFIG_MODULE and RELEASE to specify the require version and the location of EPICS base. Having done so, run

$ make build
$ make install

To test your build, run

$ source ${EPICS_BASE}/require/${E3_REQUIRE_VERSION}/bin/setE3Env.bash
$ iocsh

which should start up an IOC and load require.