3.3.2 TURBOchannel Configuration (TCCONFIG) Register—1.C200.0008
The TURBOchannel ASIC configuration register indicates the page size and the
DMA buffer threshold number.
The TCCONFIG register should be written only by powerup code in the console
ROM. It consists of two fields:
• Bit 8 is the page-size field, specifying 8-KB or 512-byte pages to the hardware.
• Bits 0-4 specify the DMA buffer threshold for a read operation; after the
transferred data reach the amount specified by this threshold, the hardware
requests more data from the memory.
If the threshold number is too small, incorrect data may be sent to the
TURBOchannel. If the threshold number is too large, data in the DMA buffer
may be overwritten and wrong data may be sent to the TURBOchannel. The
current value is 22.
The register’s format and contents are:
07 05 04 0009 0831
MR−0070−93RAGS
0 P 0 MAGIC #
Bits Access Init. Description
4:0 R/W 16 Magic #—DMA holdoff threshold count
7:5 0 Reserved
8 R/W 0
Page size;
1 = 512 bytes
0 = 8K bytes
31:9 0 Reserved
3–12 TURBOchannel I/O Registers
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