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# SPDX-License-Identifier: GPL-2.0-or-later
# Description:
# Measure the CPU clock frequency of an ARM Cortex-M based device.
#
# Return:
# The CPU clock frequency in Hz. A negative value indicates that the loop
# counter was saturated.
#
# Note:
# You may need to adapt the number of cycles for your device.
#
add_help_text cortex_m_test_cpu_speed "Measure the CPU clock frequency of an ARM Cortex-M based device"
add_usage_text cortex_m_test_cpu_speed {address [timeout [cycles_per_loop]]}
proc cortex_m_test_cpu_speed { address { timeout 200 } { cycles_per_loop 4 } } {
set loop_counter_start 0xffffffff
halt
# Backup registers and memory.
set backup_regs [get_reg -force {pc r0 xPSR}]
set backup_mem [read_memory $address 16 3]
# We place the following code at the given address to measure the
# CPU clock frequency:
#
# 3801: subs r0, #1
# d1fd: bne #-2
# e7fe: b #-4
write_memory $address 16 {0x3801 0xd1fd 0xe7fe}
set_reg "pc $address r0 $loop_counter_start"
resume
sleep $timeout
halt
# Get the loop counter value from register r0.
set loop_counter_end [dict values [get_reg r0]]
set loop_counter_diff [expr {$loop_counter_start - $loop_counter_end}]
# Restore registers and memory.
set_reg $backup_regs
write_memory $address 16 $backup_mem
if { [expr {$loop_counter_end == 0}] } {
return -1
}
return [expr {double($loop_counter_diff) * $cycles_per_loop / $timeout * 1000}]
}
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