VME64x Core specifications
==========================

This core implements a VME64x slave - WB master bridge. It provides a complete
and user extendable CR/CSR space, and forward to a wishbone slave VME
transfers.  On the WB side, the addresses are rebased from 0.

Features
--------

* interrupts: 1 with automasking. Once acknowledge by the handler, interrupts
  are masked for 1ms or until deasserted by the slave. The intent is to
  prevent interrupt bursts.
* A disable ADEM (set to 0) results in an unimplemented ADER, to reduce gate
  usage.
* CSR Reset bit is handled as a pulse (will reset on the next write).
  This doesn't follow the standard, but is needed for software compatibility.
* DTACK/BERR are supposed to be released at most 30ns once DS is released.
  The design needs 4 clocks to release them, which means the min frequency
  is supposed to 133Mhz

Changes
-------

* Core is smaller (< 1000 slices)
* No retry
* No endianess convertion
* WB data bus is 32 bit
* Internal component declarations removed.
* Port function_o to be removed.

VME interface
-------------

Supported:
* D08(EO), D16, D32
* Addressing mode: A16, A24, A32
* BLT, MBLT
* D08(O), I(7-1), ROAK interrupts
* (compatible with MEN A25 master board)
* CR/CSR space with extensions from VME64x
* Geographic Address (GA), dynamic configuration (ader).
  (TODO: support noga/usega for svec ?)
* Interrupt

Not supported:
* 2eVME
* 2eSST (no hardware)
* Dynamic size (DFSR, DFS)
* Fixed address (FAF)
* Extra Function Mask (EFM)
* XAM (no 2e)
* A40, A64 (not supported by MEN A25)
* MD32 (multiplexed data cycle, only for A40)
* LCK (bus lock)
* UAT (unaligned accesses)
* RMW cycles (but should work)
* ADO, ADOH (address only cycle)
* D08, D16 for BLT (??)
* RETRY (cf rule 2.91 - incompatibility with WB)

WB interface (datasheet)
------------
*  1. Compliant to Wishbone B4 specifications
*  2. Slave
*  3. Signals name follows the specification
*  4. err_i is forwarded to VME as BERR*
*  5. rty_i is not supported
*  6. no TAGs
*  7. Port size is 32 bit
*  8. Port granularity is 8 bit
*  9. Maximum operand size is 8 bit (TBC)
* 10. Data transfer ordering is BIG ENDIAN
* 11. Sequence of data transfer is defined by the VME side
* 12. No CLK_I signal, clock is provided separately.
* Non pipeline behaviour (but compatible with pipeline).

Generics
--------

The generics define values for many CR registers, and the clock period (needed
to follow the VME timing specifications).  See generic declarations for
details.

Ports
-----

In addition to reset and clock, the ports are used for VME and WB signals,
to connect a user defined CSR or CR memory, interrupts from the WB slave,
VME irq level and vector.  See port declaration for details.

TODO:
-----

* Stick DFSR and XAM to 0
* Put FF in IOB for all VME lines


VITAL-1 rules
-------------
[ Master/D64/A64 means N/A as the rule doesn't concern this core]
2.1a: Master
2.69: Master
2.2: Followed
2.3: Followed, excluded from c_AMCAP_ALLOWED. [no TB]
2.70: D64
2.7: Followed
2.8: Followed
2.9: Followed
2.71: A64
2.10: Master
2.11: Followed
2.72: A64
2.73: A40
2.74: Followed (A32, A24, A16 supported)
2.75: Followed (likewise)
2.76: Followed (D16 and D08(EO) supported)
2.77: Followed (likewise)
2.4: Followed (D32 supported)
2.5: Followed (D16 supported)
2.12a: Master
2.78: Master
2.66: Followed
2.79: Master
2.80: Master
2.6: Followed [no TB]
2.68: Followed [no TB]
2.81: Followed (LOCK not accepted)
2.82: Followed (likewise)
2.83: Master
2.84: Followed (lock)
2.85: Followed (CR/CSR layout)
2.86: Followed
2.87: Followed (D08(O) is the data access supported)
2.93: Master
2.18: Followed (A[] and LWORD lines are registered)
2.19: Master
2.20: Master
2.21: Master
2.22: Master
2.23: Master
2.24: Master
2.25: Followed (DATA lines are all driven for read, MBLT not supported)
2.26: Followed (Likewise)
2.27: Master
2.28: Master
2.29: Master
2.30: Master
2.31: Master
2.32: Master
2.33a: Master
2.34a: Master
2.35: Master
2.36: Master
2.37: Master
2.38: Master
2.39: Master
2.40: Master
2.41: Master
2.42: Master
2.43: Master
2.44a: Master
2.94: Master
2.45: Master
2.46a: Master
2.47a: Master
2.48a: Master
2.49: Master
2.50: Master
2.51: Master
2.52: Master
2.95: Master
2.96: Master
2.53a: Followed (VME_DATA_DIR is set only once DSA goes low)
2.54a: Followed
2.55: Followed (number of states in the main FSM + synch FF)
2.28a: Followed (likewise)
2.56a: Followed
2.57: Followed
2.98: TBC
2.58a: Followed (released at the same time)
2.99: TBC (retry)
2.100: TBC (retry)
2.101: TBC (retry)
2.102: TBC (retry)
2.103: TBC (retry)
2.104: TBC (retry)
2.105: TBC (retry)
2.59: Bus timer
2.60: Bus timer

3.x: Arbitration

4.1: Backplace
4.50: Followed (slave can generate interrupt)
4.2 Followed


Perf
----

A24 SCT DMA 0x3d
Read Rate: 10.270429 MB/sec
Write Rate: 10.765994 MB/sec

A24 BLT DMA
Read  Rate: 8.782308 MB/sec
Write Rate: 9.176580 MB/sec

A24 MBLT DMA
Read  Rate: 15.769639 MB/sec
Write Rate: 17.178069 MB/sec
