Bugfixes in the scheduling library

[phanikishoreg]

Summary of this Pull Request (PR)

Many of the changes are a result of debugging in rump2cos env and I figured it is useful to merge asap as it includes fundamental parts of the sl like sl_thd_aep_alloc() bug.

Major changes: sched lib:

• Fixed tcap budget management and handle -EPERM (no budget with tcap) from dispatch functionality
• Removed SL_THD_WOKEN state and allow redundant scheduling events
• fixed sl_thd_aep_alloc() functions to use static cos_aep_info structs!
• changed sl_init() to allow period to be passed for hierarchical timeout granularities.
• fixed a bug related to dropping of scheduling events in sl_sched_loop. [This was detected from static analysis of the code and not from any test.]

kernel:

• undo redundant scheduling events for asnds and removed budget expiry events - perhaps revisit this
• disable preemption-stack code - need to revisit
• a bug in cos_sched_rcv for root scheduler because root scheduler doesn't really get suspend, output values were garbage because of register reuse in this system call.
• a bug when tcap expended logic decided to resume execution of the same "scheduler" thread from cos_sched_rcv, the registers were not restored correctly.

Intent for your PR

Choose one (Mandatory):

• [ ] This PR is for a code-review and is intended to get feedback, but not to be pulled yet.
• [x] This PR is mature, and ready to be integrated into the repo.

Reviewers (Mandatory):

@gparmer

Code Quality

As part of this pull request, I've considered the following:

Style:

• [x] Comments adhere to the Style Guide (SG)
• [x] Spacing adhere's to the SG
• [x] Naming adhere's to the SG
• [x] All other aspects of the SG are adhered to, or exceptions are justified in this pull request
• [ ] I have run the auto formatter on my code before submitting this PR (see doc/auto_formatter.md for instructions)

Code Craftsmanship:

• [x] I've made an attempt to remove all redundant code
• [x] I've considered ways in which my changes might impact existing code, and cleaned it up
• [x] I've formatted the code in an effort to make it easier to read (proper error handling, function use, etc...)
• [x] I've commented appropriately where code is tricky
• [x] I agree that there is no "throw-away" code, and that code in this PR is of high quality

Testing

I've tested the code using the following test programs (provide list here):

• micro_booter, vkernel_boot, unit_fprr, unit_schedtests, unit_defci
• tested in rump2cos env (where bugs were originally uncovered!)

[phanikishoreg]

Thank you for the review, I've had to fix 2 other bugs and will include that in this PR. Sorry for the delayed response to your review.

[phanikishoreg]

@gparmer I've updated the PR with fixes for your previous feedback and other bugs identified either in testing or static analysis. Please review, thank you!

[phanikishoreg]

Thank you for the merge, there is a bug in my usage of PS lib fixed that and created a new PR.