Specifications

©Copyright 2001-2013 SD Group (Panasonic, SanDisk, Toshiba) and SD Card Association
Physical Layer Simplified Specification Version 4.10
108
4.14 Erase Timeout Calculation
This chapter provides the guideline for long erase and a method to calculate erase timeout value.
4.14.1 Erase Unit
The Speed Class Specification defines a new management unit of AU (Allocation Unit). Erase timeout
calculation is defined as the basis of AU. SD memory card supports block erase but it takes more time
to erase blocks, which are part of AU (partial erase AU). In this case, the host should add 250 ms to the
result of timeout calculated on AU basis. When the start and end blocks are in the same partially erase
AU, 500ms should be added.
4.14.2 Case Analysis of Erase Time Characteristics
Figure 4-56 shows an example of erase characteristics, number of AU erased versus erase time. Erase
time is derived from erasing specified numbers of AUs by one erase command. Assuming that Erase is
performed on AU basis and its erase characteristics can be approximated to a linear line. The line A
illustrated in Figure 4-56 is an example characteristic.
The red line indicates the erase timeout value the host should use. The timeout value can be
determined by line A. If the erase timeout is less than 1 second the host should use 1 second as
timeout. If the timeout is bigger than 1 second the host should use the value determined by Line A.
Register parameters N
ERASE
, T
ERASE
and T
OFFSET
define the shape of the line. T
ERASE
indicates timeout
for erasing N
ERASE
AUs from T
OFFSET
. T
ERASE
and N
ERASE
determine the slope of the line. T
OFFSET
adjusts
the line by moving in parallel on the upper side. The card manufacturer shall determine these
parameters so that the line is always greater than the erase time of any AUs. Actual erase time shall be
always less than erase timeout and the slope of the line shall be less than 3 second per AU.
Figure 4-56: Example Erase Characteristics (Case 1 TOFFSET=0)
0
1 2
Number of AU Erased
Erase Timeout [Sec]
N
ERASE
1
2
3
Line A
T
OFFSET
3
T
ERASE