ARM ARM7TDMI User Manual Page 154

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Debugging Your System
5-50 Copyright © 2001 ARM Limited. All rights reserved. ARM DDI 0234B
A register is read by shifting its address into the address field, and by shifting a 0 into
the read/write bit. The 32-bit data field is ignored.
The register addresses are shown in Table 5-1 on page 5-17.
Note
A read or write actually takes place when the TAP controller enters the UPDATE-DR
state.
5.20.2 Using the data, and address mask registers
For each value register in a register pair, there is a mask register of the same format.
Setting a bit to 1 in the mask register has the effect of making the corresponding bit in
the value register disregarded in the comparison.
For example, when a watchpoint is required on a particular memory location, but the
data value is irrelevant, the data mask register can be programmed to
0xffffffff
(all bits
set to 1) to ignore the entire data bus field.
Note
The mask is an XNOR mask rather than a conventional AND mask. When a mask bit is
set to 1, the comparator for that bit position always matches, irrespective of the value
register or the input value.
Setting the mask bit to 0 means that the comparator matches only if the input value
matches the value programmed into the value register.
5.20.3 The control registers
The control value and control mask registers are mapped identically in the lower eight
bits, as shown in Figure 5-13.
Figure 5-13 Watchpoint control value, and mask format
Bit 8 of the control value register is the ENABLE bit and cannot be masked.
ENABLE CHAINRANGE DBGEXT PROT[0]PROT[1] SIZE[1] WRITESIZE[0]
8 67 5 34 2 01
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