VME AddressAsignment Considerations

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Considerations when using the F1TDC with other boards in a VME Crate

One area that a user can shoot himself in the foot when populating a VME crate for use in an experiment is with overlapping address spaces between boards in the crate. This can be particularly difficult when there are different types of modules from different vendors. If addresses between boards do overlap this can cause unpredicable behavior that may not always be detectable, AND CAN RESULT IN CORRUPTED DATA BEING ACQUIRED.

The note provides a few guidelines and an example when using a JLAB F1 TDC with a CAEN v792 ADC in the same crate.

VME Address Spaces

There are 3 general address spaces that VME boards can be designed to respond to. These are defined as A32, A24 and A16, and they are all distict and can coexist. They are defined by the number of bits necessary to define the address (namely 32, 24, or 16 bits).

      A32  -   0xffffffff - 0        4 GBytes of Addressable space
      A24  -   0x00ffffff - 0        16MBytes of Addressable space
      A16  -   0x0000ffff - 0        64KBytes of Addressable space

You will note that A16 is contained within A24 which is contained within A32 so there can be an ambiguity as to what address space is intended. For this VME specifies a 8 bit "address modifier" (AM) tag to denote which address space is intended. Hence, when an address cycle is issued on the VME Bus not only are the address bits driven, but there are the 8 additional bus lines that specify the Modifier (a total of 40 bits of info).

A VME board will monitor these lines to determine if the address cycle was intended for it. If so then it will begin a data cycle for reading or writing. If two boards in the crate think the cycle is for them then they will both attempt to read/write on the bus - which can be the cause of many problems.

F1TDC Address Map

The F1 TDC is programed to respond to both A24 and A32 address cycles. The range of A24 addresses it will respond to is defined by the micro switches on the board itself. The user can adjust bits A12 - A23 (the high 12 bits of A24). Based on this choice an F1 board can then respond to any A24 address between the BASE (set by the switches) and 4KBytes above the base:

    e.g.    Base set to  0xed0000   (A23-A12 -> 0xED0)
         Then the board will respond to addresses between 0xed0000 - 0xed0fff.

The F1 TDC can also respond to A32 addresses, but this must be programmed into registers (via A24 access) on the board. All data must be read out via A32 access. There are two available windows. This is done automatically in the f1tdcLib when the f1Init() function is called. Based on the number of F1 boards in the crate each board will allocate a 4MByte window. If there is more than 1 board in the crate then a second 16MB "common" window will be created for all boards. This window is ment to be the same for all boards because it is used for Multi-Block transfers. The A32 base address starts at 0x08000000 (128 MBytes).

  For 1 F1 in a crate there will be one A32 window active
         A32   0x08000000 - 0x083fffff   (4MB)
  For 3 F1s in a crate there are four A32 windows active
       1)   A32   0x08000000 - 0x083fffff   (4MB)
       2)   A32   0x08400000 - 0x087fffff   (4MB)
       3)   A32   0x08800000 - 0x08bfffff   (4MB)
              (4MB Blank space)
       4)   A32   0x09000000 - 0x09ffffff   (16MB) (common to all boards)

Other Boards

Any other types of boards that will be used in the crate need to be configured so that they do not overlap any of the address space that the F1 TDCs use. You must consult the manual for the third party board you are interested in using.

I will use a CAEN V792 ADC as an example to show how to set the switches so that they will not interfere with the F1s.

The V792 has 4 switches that define both an A32 and A24 address space in VME. This board will always have both windows active no mater how many boards are in the crate. There are additional options for programming a common address space but the library c792Lib.o does not support this feature.

The user can set the Address bits A31 - A16 (16bits). Once the base is set a single v792 will respond to any address cycle between the base and 64Kbyes above the base.

    e.g.   Set bits A31 - A16  to  0x08aa via the switches.

         A24 active space -    0xaa0000 -   0xaaffff.
         A32 active space -  0x08aa0000 - 0x08aaffff.

Note that this these are completely duplicate address spaces. If you access the address 0xaa0000 in A24 space this will read the exact same register on the same board as 0x08aa0000 in A32 space. Note also that if you have a v792 set up this way with a single F1 in the crate as well then there would be NO address conflicts. However if you had more than one F1 in the crate then there WOULD be overlaps in A32 space.

Block Reads (DMA issues)

The fastest way to read out either the F1 or the v792 is with a VME block read. This is accomplished through use of the DMA engine on the VME-PCI bridge (called the Universe chip). There is a seperate library that must be downloaded to enable the use of block reads from either board's library (f1tdcLib.o or c792Lib.o). This library is called "universeDma.o".

The universe DMA engine must be set up to define which address space it will attempt to access (A24 or A32). For the F1 A32 is the only option. For the v792 one can read data from either A24 or A32.

 Sample Universe DMA setup:
     /*initialize (no interrupts) */
     /*Set for 64bit PCI transfers */
     /* A24 (1) or A32 VME Slave (2)*/
     /* BLK32 (4) or MBLK64 (5) VME transfers */

If the user wishes to support block reads from both an F1 and a v792 board in the same crate using the existing libraries then the v792 must be initialized to access the board from its A32 window (not A24). This is done by setting the swtiches and calling c792Init() using the full A32 address (e.g. 0x08aa0000). The universe chip should be set to access an A32 VME slave. This way both block read functions for each boards library should function properly.

      • NOTE:

The universe library universeDma.o had to be modified in order to support the F1 Multiblock readout. As a conseqence the v792 ADC block read function (c792ReadBlock()) does not work with the new universeDma library. The c792Lib.o had to be updated to fix the problem. Please make sure you are using the latest versions of all three of the libraries if you wish to use them for a mixed crate configuration.

They can be found in: /site/coda/2.5/extensions/

Any questions please direct to David Abbott (x7190) abbottd@jlab.org