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STM32 Bare-Metal Clock Setup | Register-Level Programming
Aug 11, 2020
In this tutorial, we will configure the STM32 system clock using registers only, without relying on HAL, SPL, or LL libraries. This is the very first step in mastering bare-metal STM32 programming, where we directly manipulate registers for complete control. We will go through the clock setup step by step, verify the configuration by blinking an LED, and prepare the foundation for upcoming tutorials. In the next part, we will use STM32 timers to generate accurate delays in microseconds and milliseconds. 📂 Download Project Files: [https://controllerstech.com/stm32-clock-setup-using-registers/] 📺 Watch Related Tutorials: STM32103 Clock Configuration : https://youtu.be/Ke_jD_2ILMU Configure Timer to Generate Delay : https://youtu.be/iImNVKJCq4Q?si=wCnh4U7DVAoKri2Y 🔔 Don’t forget to subscribe and follow the playlist for the full STM32 Register Programming series! #STM32 #EmbeddedSystems #Microcontroller #RegisterProgramming #STM32Tutorial #STM32F4 #ClockSetup #BareMetalProgramming
View Video Transcript
0:01
[Music]
0:09
hello
0:10
everyone welcome to controllers tech
0:14
this video is the start of a new series
0:16
and in this series i will cover the
0:18
stm32 register level programming
0:22
this is the first video and today we
0:24
will see how to set up the clock
0:27
and that's why this video is going to be
0:29
very long
0:31
there are no shortcuts here some
0:33
registers and values might be different
0:35
for your controller
0:36
and that's why you need to see the
0:38
entire process
0:40
i will use kyle for these tutorials
0:44
let's open the pack installer first
0:47
type your mcu name and let it refresh
0:50
the database
0:58
now you need to install the dfp pack
1:01
from here
1:02
that will be all you need
1:07
also make sure the compiler is updated
1:11
i already have them installed and
1:13
updated
1:24
go to project and create a new project
1:33
give the name to this project and click
1:38
save
1:47
search for your device here
1:53
[Music]
1:58
we only need to include the core file
2:01
and startup
2:02
file from here
2:08
here is our project let's add the main
2:11
file to this
2:19
first of all include the device specific
2:22
file
2:24
[Music]
2:27
this file have all the registers irq
2:30
predefined in it
2:36
i am going to create a main function and
2:38
a while loop inside it
2:44
let's create a function where we will
2:46
configure the clock
2:50
and here are the steps that i am going
2:52
to follow
2:54
first we need to enable the external
2:56
crystal
2:57
and wait for it to become ready then
3:00
enable the power
3:01
and configure the voltage regulator
3:04
next we need to configure the flash
3:07
related settings
3:09
then configure the prescalers for
3:11
peripheral clocks
3:13
then configure the pll then enable the
3:17
pll
3:18
and finally select the pll as the clock
3:20
source
3:25
we will cover all these steps one by one
3:29
let's also open the cube mx for the
3:44
reference
3:59
i am selecting external crystal for the
4:01
clock
4:03
i will configure for the maximum clock
4:05
here because i always prefer it
4:07
and this way i can keep the same
4:09
settings for the other programs too
4:23
we will come back to this once we start
4:26
programming
4:33
let's start with the first step
4:36
so we need to turn the hse on
4:40
and wait for it to become ready
4:44
this bit is in the rcc cr register
4:53
as you can see here the 16th bit is for
4:56
hse on
4:57
and the 17th bit is the hse ready bit
5:07
in the rcc cr register set the hse
5:12
on bit
5:13
[Music]
5:18
this is already defined in the header
5:20
file and it's basically writing a 1
5:23
at 16th position now we will wait for
5:26
the hse ready bit
5:28
to set in the cr register
5:30
[Music]
5:35
this will indicate that the hse crystal
5:38
is on
5:39
let's move to the second step enable the
5:43
power interface clock
5:44
and configure the voltage regulator
5:55
power enable is 28th bit of the rcc apb1
6:04
register
6:12
we will set this bit in order to enable
6:15
[Music]
6:18
it now the setting for the voltage
6:21
regulator
6:24
[Music]
6:31
this bit is located in power control
6:33
register
6:34
and it's the bit number 14 and 15.
6:43
just keep this to its reset value in
6:45
this case it will be 1
6:47
1.
6:57
the vos will always correspond to the
6:59
reset value
7:06
now the step 3 we need to configure the
7:10
flash related setup
7:12
to do so we need to modify the flash
7:15
access control
7:16
register
7:20
let's see the cube mx here we have all
7:24
instruction cache
7:25
prefetch buffer data cache all are
7:28
enabled
7:29
and the flash latency is 5ws
7:40
all these bits are available in access
7:42
control register
7:51
let's set the flash acr register
7:56
accordingly
8:10
do
8:12
now the fourth step is to configure the
8:14
prescalers for the main clock
8:16
and the peripheral clocks
8:26
as you can see here apb1 prescaler is 4
8:30
apb2 prescaler is 2 and ahb prescaler is
8:34
[Music]
8:38
1.
8:43
all these configuration bits are in our
8:45
cc clock configuration register
8:59
let's first set the ahb prescaler
9:03
ahb prescaler is one in our setup
9:06
so i am using division 1.
9:14
next set the abp1 prescaler which have
9:18
the value 4
9:19
so division 4.
9:29
and at last set the apd2 prescaler
9:32
whose value is 2 and that's why division
9:35
2.
9:36
let's move to the fifth step and
9:38
configure the pll
9:46
we will do that by modifying the rccpll
9:50
configuration register here we need to
9:53
set the values of pllm
9:55
and plln p q and r
10:06
you can see the values here pllm is for
10:10
plln is 180
10:13
and pllp is 2.
10:29
let's define these values first
10:49
in the pllm we can directly input the
10:52
value at the bit 0.
10:54
similarly in plln we can input the value
10:58
at bit 6 directly
11:05
but in pllp we can't directly use the
11:08
values
11:09
as we need to select from these
11:11
available here
11:12
i have the pllp as 2 so i need to write
11:16
0 to this 16th position
11:24
so i will simply shift this 0 to the
11:27
sixteenth position
11:35
let's modify the pll configuration
11:38
register now
11:40
p l l m starts at bit zero
11:44
p l l n starts at bit six
11:54
p pllp starts at bit 16.
11:58
here we also need to select the source
12:00
of pll
12:02
which in this case is hse oscillator and
12:05
i need to write a 1 a 22nd bit
12:20
in step 6 we need to enable the pll
12:32
in our cc control register bit 24
12:35
enables the pll
12:37
and bit 25 confirms the ready status
12:49
let's enable the pll first and now we
12:52
will wait for the pll to become ready
13:03
the final step is to set the clock
13:05
source
13:10
this can be done in the rcc
13:12
configuration register
13:15
the zeroth bit is to set the clock
13:17
source and the second bit is to confirm
13:19
the status
13:21
here i will use the pllp as the clock
13:24
source
13:26
set the pll as the clock source
13:30
and wait for the source to become ready
13:42
this completes the clock setup now from
13:46
now onward
13:47
in most of these videos i will use these
13:49
settings as it is
13:52
so this was basically just a one-time
13:54
setup
13:57
[Music]
13:58
now as we want to blink the led we need
14:01
to configure the gpio
14:05
here the things are easy just enable the
14:08
gpio clock
14:10
set the pin as output and configure any
14:12
settings you need for the output mode
14:16
let's start with the first one to enable
14:19
the gpio clock
14:21
we need to look into a cc peripheral
14:24
clock enable register
14:26
as you can see here the zeroth bit of
14:29
this register
14:30
enables the gpio clock
14:37
by the way i am using pin pa5 for the
14:40
led
14:43
write a one to the zeroth position to
14:45
enable the clock for gpioa
14:49
in the second step we'll set the pin as
14:56
output
14:58
this can be done using gp io mode
15:01
register
15:06
here we need to write a 0 and 1 to set
15:09
the pin as output
15:12
every two bits of this register controls
15:14
a single pin
15:16
for example bits 0 and 1 controls the
15:20
pin 0
15:21
bits 2 and 3 controls the pin 1 bits 4
15:24
and 5
15:24
controls the pin 2 and similarly bits 30
15:28
and 31
15:29
controls the pin 15. as i need to set
15:33
the pin
15:33
5 as the output i need to modify bits 10
15:36
and 11 so 11th bit will be 0 and 10th
15:40
bit will be 1.
15:49
in the gpioa mode register
15:52
i will write a 1 in the 10th position
15:55
and 11th position is 0 by default
16:02
now the last step is to configure the
16:04
output mode
16:06
like what type of output we want
16:09
default setup is for push-pull and this
16:11
is exactly what we need
16:19
then we have the type of speed we want
16:21
for the output pin
16:23
by default its low speed i am okay with
16:26
it
16:27
since i am only blinking led for now
16:30
the there is pull up or pull down
16:32
configuration
16:34
we will leave this to none since we are
16:36
using the pin
16:37
for blinking so all the remaining
16:40
registers should be zero
16:42
even if you don't write values to them
16:44
they will be zero by default
16:47
i will write them anyway
16:51
this finishes up the gpio configuration
16:56
let's write the main function now
16:59
first of all set the system clock and
17:02
then set the gpio
17:05
and now on the while loop i need to
17:07
toggle the pin pa5
17:10
to set or reset a pin we need to use the
17:13
gpio bit set reset register
17:17
as you can see here to set a pin we need
17:20
to set it in the lower half of the
17:22
register
17:24
and in order to reset the pin we need to
17:26
write a 1
17:27
in the upper half
17:32
as i am setting pin p-a-5 i will write
17:35
the fifth bit of this register to 1.
17:38
let's give some delay which i will cover
17:41
later
17:42
now to reset the pin 5 i need to write a
17:45
1 to the upper half of this register
17:48
as you see here the upper half starts at
17:51
bit 16
17:52
so the pin 5 will be the 21st bit and to
17:55
reset it
17:56
i need to write a 1 in 21st position
18:00
instead of doing that i will simply
18:02
write a 1 to the 5th position
18:04
and shift the entire value by 16 places
18:08
and again give the delay for toggling
18:11
let's create that delay function
18:15
this is just some random wait time
18:18
let's build this
18:19
[Music]
18:23
we don't have any errors here go to
18:26
options
18:27
and update the frequency here mind will
18:30
be running at 180 megahertz
18:34
select the st link debugger
18:39
select connect under reset
18:44
and reset and run
18:45
[Music]
18:49
click download to flash the code
18:56
you can see the led is blinking but it's
18:59
too fast to be noticed
19:01
[Music]
19:04
let's increase the delay
19:12
[Music]
19:18
now the blinking is perfect
19:26
let's modify it one last time
19:42
and you can see now it's even more
19:44
slower
19:49
so that's all for this video i will
19:53
continue this series
19:54
and we will cover all sort of
19:56
peripherals here
19:58
also a cc was just one time setup
20:01
and next video onward i will simply
20:04
include it in the main file directly
20:06
i hope you learned something today
20:09
things can be a bit hard in the
20:11
beginning especially if you have never
20:13
worked with registers before
20:16
but you have to start somewhere in the
20:19
next video
20:20
i will cover the basic feature of the
20:22
timer and we will use it to generate the
20:24
proper time delay
20:26
goodbye till then keep watching and have
20:29
a nice day
20:38
you
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