Adding the test registers at known address locations.

[wzab]

That functionality has been requested by @wfjm as the result of usage of AGWB for preparation of the CBM firmware. The idea is that at well known positions the following registers should be located:

• TEST_RW - normal read/write register.
• TEST_WO - the write only register. Writing stores the data that may be read via the next register. Reading generates an error.
• TEST_RO - the read only register. Reading returns the last data written to TEST_WO.
• TEST_TOUT - any access to that register generates the bus timeout.

The implementation may be relatively simple and requires just simple extension of the code generation template: https://github.com/wzab/agwb/blob/c35cde4f73a2fee4b715908942afc4082426e13a/src/wb_block.py#L176

The feature should be optional (so an additional attribute, e.g. testdev_ena="1" should be added). Depending on it, the address of the first free register should be adjusted in: https://github.com/wzab/agwb/blob/c35cde4f73a2fee4b715908942afc4082426e13a/src/wb_block.py#L1244

[wzab]

With introduction of new "fixed" registers it should be decided if they should be still manually added in all target address maps, as it is done now:

https://github.com/wzab/agwb/blob/c35cde4f73a2fee4b715908942afc4082426e13a/src/wb_block.py#L1590

https://github.com/wzab/agwb/blob/c35cde4f73a2fee4b715908942afc4082426e13a/src/wb_block.py#L1674

https://github.com/wzab/agwb/blob/c35cde4f73a2fee4b715908942afc4082426e13a/src/wb_block.py#L1742

https://github.com/wzab/agwb/blob/c35cde4f73a2fee4b715908942afc4082426e13a/src/wb_block.py#L1853

https://github.com/wzab/agwb/blob/c35cde4f73a2fee4b715908942afc4082426e13a/src/wb_block.py#L1925

https://github.com/wzab/agwb/blob/c35cde4f73a2fee4b715908942afc4082426e13a/src/wb_block.py#L1999

Maybe it would be better to implement a list of such "fixed" registers and handle them automatically in target address maps generators? With 4 registers used in TEST DEVICE we can survive with manual implementation, but if there are more to come, maybe we should change it?

[wzab]

The required functionality is implemented with commit https://github.com/wzab/agwb/commit/081e8403b6779a27dc202caf206492bdb692bce2 and initially tested in commit https://github.com/wzab/agwb/commit/8ae93f4acd2dff89c6a0af9ad32de8e89481aee2

Many thanks to Walter F.J. Müller @wfjm for suggesting that functionality.

The target code generators, however, are becoming complex, and difficult to maintain. Maybe it is time to rethink how to separate them and clean them up, as suggested by @m-kru in #43 ?