The xVME register class is used for single cycle VME accesses.
The register value is a data item of length (in bits) given by the -l attribute which occupies a field in the VME data word with least significant bit given by the -b attribute. Whole words can be accessed by setting the length and bit attributes to zero (the default values).
The class accepts data values in decimal, hexadecimal or binary format.
All address variables are VME addresses and are thus expressed in units of bytes (8 bits).
Register values for the xVME class are text strings.
Attributes :-
-a VME base address
specifies the start address of the data area as a VME address.
-o offset
specifies the address offset of the access relative to the base of the data area.
-w width of VME address in bits. Options are 16; 24; 32.
specifies the address width required for accesses to the VME hardware.
-d width of VME data access in bits. Options are 8; 16; 32.
specifies the data width required for accesses to the VME hardware.
-u use. Options are d (data); p (program).
specifies the use required for accesses to the VME hardware.
-m mode. Options are n (non-privileged); s (supervisory).
specifies the mode required for accesses to the VME hardware.
-m VME address modifier.
specifies the address modifier required for accesses to the VME hardware.
If a numeric value is supplied this is taken to be a VME address modifier and the -u and -w attributes are ignored. Otherwise the -m, -u and -w attributes are taken to define the VME address modifier.
-p access permission (rw, ro, wo)
specifies the data access modes permitted to the VME hardware.
Options are ro (read only); wo (write only); rw (read-write).
-l length of bit field
specifies the length of the data field for this register in bits.
The server code permits access to VME hardware registers at the bit level.
The hardware will always be accessed using the access width specified by the -d attribute.
The server however implements in software objects which may be any subfield of a hardware register.
For write access to a subfield of a hardware register it is required that the hardware be readable.
The attribute value -l 0 implies that the data field for this object is the same as the hardware
access width specified by the -d attribute. Optional. By default -l 0 is assumed.
-b bit position
specifies the position of the least significant bit of the data within the hardware register.
The hardware is addressed with the least significant bit having the value 0.
This attribute will normally always be used in conjunction with the -l attribute to define
the length and position of a software object which is a subfield of the hardware register.
Optional. By default -b 0 is assumed.
-z data format
specifies the data format to be used by READ operations. Data can be return in decimal (d),
hexadecimal (x) or binary (b). The default is hexadecimal.
-i initial value
specifies the data value to be used by the INITIALISE operation. The register must also have
write permission.
-s status switch
If s = 1 then access status is returned as a second data item for READ operations in the form %s. (Default is s=0)
default attributes : -a 0x0 -o 0x0 -w 32 -d 32 -u d -m n -p rw -l 0 -b 0 -z x -s 0
The default address modifier is thus 0x09 (A32 data access non-privileged)
The default attribute value is used for any attribute not defined by a write-attributes procedure call.
data for write operations may be supplied in any format but the data format attribute (-z) will determine the format used when returning data for read operations.
The absolute VME address used is given by base address + offset.
The INITIALISE operation is permitted only for regsiters having access attribute rw or wo and will only write data to VME if an initial value has been explicitly defined by the -i attribute.