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#----------------------------------------
# Purpose - Create some $BIT variables
# Create $K and $M variables
# and some bit field extraction variables.
# Creat helper variables ...
# BIT0.. BIT31
for { set x 0 } { $x < 32 } { set x [expr $x + 1]} {
set vn [format "BIT%d" $x]
global $vn
set $vn [expr (1 << $x)]
}
# Create K bytes values
# __1K ... to __2048K
for { set x 1 } { $x < 2048 } { set x [expr $x * 2]} {
set vn [format "__%dK" $x]
global $vn
set $vn [expr (1024 * $x)]
}
# Create M bytes values
# __1M ... to __2048K
for { set x 1 } { $x < 2048 } { set x [expr $x * 2]} {
set vn [format "__%dM" $x]
global $vn
set $vn [expr (1024 * 1024 * $x)]
}
proc create_mask { MSB LSB } {
return [expr (((1 << ($MSB - $LSB + 1))-1) << $LSB)]
}
# Cut Bits $MSB to $LSB out of this value.
# Example: % format "0x%08x" [extract_bitfield 0x12345678 27 16]
# Result: 0x02340000
proc extract_bitfield { VALUE MSB LSB } {
return [expr [create_mask $MSB $LSB] & $VALUE]
}
# Cut bits $MSB to $LSB out of this value
# and shift (normalize) them down to bit 0.
#
# Example: % format "0x%08x" [normalize_bitfield 0x12345678 27 16]
# Result: 0x00000234
#
proc normalize_bitfield { VALUE MSB LSB } {
return [expr [extract_bitfield $VALUE $MSB $LSB ] >> $LSB]
}
proc show_normalize_bitfield { VALUE MSB LSB } {
set m [create_mask $MSB $LSB]
set mr [expr $VALUE & $m]
set sr [expr $mr >> $LSB]
echo [format "((0x%08x & 0x%08x) -> 0x%08x) >> %2d => (0x%x) %5d " $VALUE $m $mr $LSB $sr $sr]
return $sr
}
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