Chapter 6
Theory of Operation
© National Instruments Corporation
6-25
GPIB-1014 User Manual
Sources of errors are as follows:
•
Configuration Error
This occurs when any undefined or reserved bit pattern, or illegal
device/operand size combination is programmed into a channel and
an attempt is made to set the STR bit. This error occurs, for
example, when chaining is programmed and the continue bit is also
set, if the DTYP bit specifies a single-address transfer and the
device port size is not the same as the operand size, or if DTYP is
68000 or 6800 (DPS is 16 bits), SIZE is eight bits, and REQG is 10
bits or 11 bits (request pin). Setting an undefined configuration
signals a configuration error. The undefined configurations are :
XPM=01, MAC=11, DAC=11, CHN=01, SIZE=11. In any case,
the channel will not start.
•
Operation Timing Error
If a write access is attempted to certain registers or bits within
registers while a channel is active or if certain status bits are set, an
operation timing error occurs and the channel operation aborts if
the channel is active. This error will occur, for example, if an
attempt is made to continue an operation without STR being
simultaneously set, if the channel is not active, if an attempt to set
STR is made with ACT, COC, BTC, NPT, or ERR asserted, if an
attempt is made to write to the DCR, OCR, SCR, GCR, MAR,
DAR or MTCR with STR or ACT asserted, if an attempt to assert
CNT is made when CHN is 10 or 11, or if an attempt to assert
CNT is made when BTC and ACT are asserted.
•
Address Error
This is signaled if a word or longword operation is attempted to an
odd address.
•
Bus Error
This indicates a bus error occurred during the last bus cycle
generated by the channel.
•
Count Error
This is signaled if the MTCR or BTCR are initialized with terminal
count. A count error is signaled if a terminal count is encountered
during continue or chain processing.
•
Abort
This is signaled if the PCL was configured as an abort input and
made an active transition, or if the channel operation was aborted
by the SAB bit of the OCR. If the PCL is used as an abort input,
the PCT bit must be cleared prior to starting the channel.
The DMAC allows access to internal registers to implement error recovery procedures. If an
error occurs during a DMA transfer, appropriate information is available to the operating system
for a soft-failure operation. The operating system must be able to determine how much data was
transferred, where the data was transferred to, and what type of error occurred.
The information available to the operating system consists of the present values of the Memory
Address, Device Address and Base Address Registers, the Memory Transfer and Base Transfer
Counters, and the Control, Status, and Error Registers. After the successful completion of any