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# SPDX-License-Identifier: GPL-2.0-or-later
# Config for Raspberry Pi used as a bitbang adapter.
# https://www.raspberrypi.com/documentation/computers/raspberry-pi.html
# Supports all models with 40-pin or 26-pin GPIO connector up to Raspberry Pi 4 B
# also supports Raspberry Pi Zero, Zero W and Zero 2 W.
# Adapter speed calibration is computed from cpufreq/scaling_max_freq.
# Adjusts automatically if CPU is overclocked.
adapter driver bcm2835gpio
proc read_file { name } {
if {[catch {open $name r} fd]} {
return ""
}
set result [read $fd]
close $fd
return $result
}
proc measure_clock {} {
set result [exec vcgencmd measure_clock arm]
set clock_hz [lindex [split $result "="] 1]
expr { $clock_hz / 1000 }
}
proc get_max_cpu_clock { default } {
set clock [read_file /sys/devices/system/cpu/cpu0/cpufreq/scaling_max_freq]
if { $clock > 100000 } {
return $clock
}
# cpufreq not available. As the last resort try Broadcom's proprietary utility
if {![catch measure_clock clock] && $clock > 100000} {
return $clock
}
echo "WARNING: Host CPU clock unknown."
echo "WARNING: Using the highest possible value $default kHz as a safe default."
echo "WARNING: Expect JTAG/SWD clock significantly slower than requested."
return $default
}
set compat [read_file /proc/device-tree/compatible]
set clocks_per_timing_loop 4
if {[string match *bcm2711* $compat]} {
set speed_offset 52
} elseif {[string match *bcm2837* $compat] || [string match *bcm2710* $compat]} {
set speed_offset 34
} elseif {[string match *bcm2836* $compat] || [string match *bcm2709* $compat]} {
set speed_offset 36
} elseif {[string match *bcm2835* $compat] || [string match *bcm2708* $compat]} {
set clocks_per_timing_loop 6
set speed_offset 32
} else {
set speed_offset 32
echo "WARNING: Unknown type of the host SoC. Expect JTAG/SWD clock slower than requested."
}
set clock [get_max_cpu_clock 2000000]
set speed_coeff [expr { $clock / $clocks_per_timing_loop }]
# Transition delay calculation: SPEED_COEFF/khz - SPEED_OFFSET
# The coefficients depend on system clock and CPU frequency scaling.
bcm2835gpio speed_coeffs $speed_coeff $speed_offset
source [find interface/raspberrypi-gpio-connector.cfg]
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