Chunky planar data packing apparatus and method for a video memory

DETAILED DESCRIPTION An apparatus and method for taking data that is presented on a 32-bit bus (e.
g.
, NUBUS) in one format and writing it into a video memory in chunky planar format, is described.
The present invention is also useful for performing RGB reads wherein video data is read from the video memory in chunky planar format and is translated into NUBUS format for transmission across the NUBUS.
Chunky planar format represents a more efficient way of packing data in video memory to eliminate vacancies in the sequence of bytes.
According to one embodiment, the apparatus comprises a data format translator which is coupled to the NUBUS for translating the RGB data from NUBUS format to chunky planar format.
The translated RGB data in chunky planar format is compressed and rearranged as compared to the NUBUS format.
The translator presents the translated RGB data (in chunky planar format) to the video memory for storage therein.
An address generator is also coupled to the video memory for calculating the address location in the video memory where the translated RGB data is to be written.
The address location is derived from the NUBUS address according to the formula N.
sub.
start =(3*NAD/4) where N.
sub.
start is the start address in video memory and NAD represents the NUBUS address from which the RGB data to be translated is obtained.
Control logic coupled to both the translator and the address generator controls the operation of the apparatus so that a single byte is translated in a single memory cycle.
The process of writing RGB data from NUBUS to video memory is initiated when a NUBUS address is received from the NUBUS.
That address is then translated to a start address in video memory according to the above formula.
Next, the individual data byte to be translated is obtained from the NUBUS and a memory cycle is initiated to write that data into the memory at the specific memory address and byte location calculated by the address generator.
Other aspects of the present invention will be apparent from the detailed description