ARM Embedded Tutorial - Raspberry Pi Pico Blinking the onboard LED
Finally we are ready to craft some code. To make things easier I have created a git repository that hosts the examples and extra binaries needed for successfully building the code.
Please close this repository:
Our first version of the blinking LED theme will stay close to the example provided by the Raspberry Foundation in their pico examples repository on github. The code will look pretty much the same as the C-Code, we will also re-use code already done by the Foundation by linking to object files from the SDK.
This technique is helpfull when you want to get working results fast, we can already get something going without the need for us to fully understand the new Microcontroller Architecture.
The main Pascal Code will look like this:
const
LED_PIN=25;
GPIO_OUT=true;
var
i : longWord;
begin
runtime_init;
gpio_init(LED_PIN);
gpio_set_dir(LED_PIN,GPIO_OUT);
repeat
gpio_put(LED_PIN,true);
for i := 0 to 300000 do ;
gpio_put(LED_PIN,false);
for i := 0 to 300000 do ;
until 1=0;
end.
to make this code work we will need some additional components, first of all we need a working gpio library for the raspberry pi pico.
when you use my repo the file is already checked in, when you want to create your own version your need to follow the chapter 'Chapter 3. Blinking an LED in C' in the getting started pdf and build the C-Version of the blinking LED example.
When done search for a file named 'gpio.c.obj' that is hidden deep down in our build directory. On my mac the file is located here:
./CMakeFiles/blink.dir/Users/ring/devel/pico-sdk/src/rp2_common/hardware_gpio/gpio.c.obj
copy this file into the directory where you store code for this blinky example.
Now change the code to include this library and look up the correct definition for the functions we need from the gpio headerfiles:
program Blinky;
{$L gpio.c.obj}
procedure gpio_init(gpio : longWord); external;
procedure gpio_put(gpio : longWord; value : longBool); external;
procedure gpio_set_dir(gpio : longWord; &out : longBool); external;
procedure runtime_init;
const
RESETS_SAFE_BITS= %1111111111100110110111111;
RESETS_PRECLOCK_BITS= %0001111000100110110111110;
RESETS_POSTCLOCK_BITS=%1110000111000000000000001;
begin
resets.reset_set := RESETS_SAFE_BITS;
resets.reset_clr := RESETS_PRECLOCK_BITS;
repeat
until (resets.reset_done and RESETS_PRECLOCK_BITS) = RESETS_PRECLOCK_BITS;
end;
and we are ready to compile our code.
As we still have a few steps of work ahead of us my recommendation is that we first use commandline to do the initial compiles as it is a little easier to see what is still necessary to fix.
We will need to use the fpc wrapper of fpcupdeluxe, so make sure you call it with the correct path of your fpcupdeluxe installation:
Windows
todo
MacOSX x86_64
$HOME/fpcupdeluxe-embedded/fpc/bin/x86_64-darwin/fpc.sh -Tembedded -Parm -Cparmv6m -Wpraspi_pico -O1 -Xu Blinky.lpr
MacOSX aarch64
$HOME/fpcupdeluxe-embedded/fpc/bin/aarch64-darwin/fpc.sh -Tembedded -Parm -Cparmv6m -Wpraspi_pico -O1 -Xu Blinky.lpr
Our code compiles, but linking fails:
Free Pascal Compiler version 3.3.1 [2021/01/25] for arm Copyright (c) 1993-2020 by Florian Klaempfl and others Target OS: Embedded Compiling Blinky.lpr Assembling blinky Linking Blinky Blinky.o: In function `main': /Users/ring/devel/rppico/Blinky//Blinky.lpr:16: undefined reference to `gpio_set_dir' /Users/ring/devel/rppico/Blinky//Blinky.lpr:18: undefined reference to `gpio_put' /Users/ring/devel/rppico/Blinky//Blinky.lpr:20: undefined reference to `gpio_put' Blinky.lpr(24) Error: Error while linking Blinky.lpr(24) Fatal: There were 1 errors compiling module, stopping Fatal: Compilation aborted Error: /Users/ring/fpcupdeluxe/fpc/bin/aarch64-darwin/ppcarm returned an error exitcode
Why's that? We saw the definitions in the gpio Headerfiles and we linked to the correct object file....
The reason is that those two functions are defined as inline and for that reason we cannot access them.
So here we need to manually create implementation, the good thing is that inlined functions are usually quite simple and our missing functions are no exception.
After reading through the gpio headerfiles we have implementations of the missing calls in pascal:
program Blinky;
{$L gpio.c.obj}
procedure gpio_init(gpio : longWord); external;
procedure runtime_init;
const
RESETS_SAFE_BITS= %1111111111100110110111111;
RESETS_PRECLOCK_BITS= %0001111000100110110111110;
RESETS_POSTCLOCK_BITS=%1110000111000000000000001;
begin
resets.reset_set := RESETS_SAFE_BITS;
resets.reset_clr := RESETS_PRECLOCK_BITS;
repeat
until (resets.reset_done and RESETS_PRECLOCK_BITS) = RESETS_PRECLOCK_BITS;
end;
procedure gpio_set_dir(gpio : longWord; &out : longbool);
var
mask : longWord;
begin
mask := 1 shl gpio;
if out = true then
sio.gpio_oe_set := mask
else
sio.gpio_oe_clr := mask;
end;
procedure gpio_put(gpio : longWord; value : boolean);
var
mask : longWord;
begin
mask := 1 shl gpio;
if value=true then
sio.gpio_set := mask
else
sio.gpio_clr := mask;
end;
const
LED_PIN=25;
GPIO_OUT=true;
var
i : longWord;
begin
runtime_init;
gpio_init(LED_PIN);
gpio_set_dir(LED_PIN,GPIO_OUT);
repeat
gpio_put(LED_PIN,true);
for i := 0 to 300000 do ;
gpio_put(LED_PIN,false);
for i := 0 to 300000 do ;
until 1=0;
end.
This approach looks a little overcomplicated at first but the gpio's are always the most simple example, for more complex peripherals like i2c or usb this approach really shines as it saves a lot of time in the end.
We now have a binary, but does it work????
To find out we need to upload the elf file to the board, a task easily done with our Debug Probe and the help of arm-none-eabi-gdb.....
First we have to connect our development board to either our Raspi-based debug probe or to the 2nd pico we converted to a picoprobe. If you have not yet prepared your debug probe read instructions on how to do so in this document:
ARM Embedded Tutorial - Raspberry Pi Pico Setting up for Development
Fire up your openocd instance:
$HOME/devel/openocd-rpi/src/openocd -f interface/picoprobe.cfg -f target/rp2040.cfg -s /Users/ring/devel/openocd-rpi/tcl Open On-Chip Debugger 0.10.0+dev-g14c0d0d33-dirty (2021-01-29-15:13) Licensed under GNU GPL v2 Info : only one transport option; autoselect 'swd' Warn : Transport "swd" was already selected adapter speed: 5000 kHz Info : Hardware thread awareness created Info : Hardware thread awareness created Info : RP2040 Flash Bank Command Info : Listening on port 6666 for tcl connections Info : Listening on port 4444 for telnet connections Info : clock speed 5000 kHz Info : SWD DPIDR 0x0bc12477 Info : SWD DLPIDR 0x00000001 Info : SWD DPIDR 0x0bc12477 Info : SWD DLPIDR 0x10000001 Info : rp2040.core0: hardware has 4 breakpoints, 2 watchpoints Info : rp2040.core1: hardware has 4 breakpoints, 2 watchpoints Info : starting gdb server for rp2040.core0 on 3333 Info : Listening on port 3333 for gdb connections
Now we can fire up our gdb and see our program run:
Windows todo
MacOSX x86_64
$HOME/fpcupdeluxe-embedded/fpc/bin/x86_64-darwin/arm-embedded-gdb Blinky.elf
MacOSX aarch64
$HOME/fpcupdeluxe-embedded/fpc/bin/aarch64-darwin/arm-embedded-gdb Blinky.elf
GNU gdb (GNU Tools for STM32 7-2018-q2-update.20190328-1800) 8.1.0.20180315-git Copyright (C) 2018 Free Software Foundation, Inc. .... Reading symbols from Blinky.elf...done. (gdb) target remote localhost:3333 Remote debugging using localhost:3333 0x00001bd0 in ?? () (gdb) load Loading section .text, size 0x748 lma 0x10000000 Loading section .data, size 0x71 lma 0x10000748 Start address 0x10000678, load size 1977 Transfer rate: 1 KB/sec, 988 bytes/write. (gdb) cont Continuing.
And you should see the LED blink......
