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Photograph
This evening, I bought a photograph from Paul Hendriksen that I had seen at the opening of the exhibition A day
in a lifetime on December 11, last year. It is
one of twenty photographs that are enlargements of a single photograph when
placed in four rows of five photographs display the original photograph. I
found this particular photograph the most interesting and Paul allowed me to
buy this single photograph. (It is relatively easy to make the series complete
again by printing the one photograph again.) While at his place, he showed me
the monograph One Tree
by Machiel Botman, one of his tutors.
Botman takes a long time, years, to compose his monographs. I fear it is
impossible to appreciate these kind books at one vieweing and that it takes
careful watching and rewatching to understand them. Probably having some formal
training in taking and printing photographs also helps appreciating and
understanding these kind of monographs. Paul also gave me some clips such that
I could put the photograph on the wall in the same manner as at the
exhibition.
Wet snow
When I walked to the office, it started to snow. Some
of the snow stayed on the ground. In some areas the snow stayed on the street,
while at other is did not. The temperature of the ground must have been around
the freezing point such that the properties of the street, such as the
blackness, played a decisive role in whether or not the snow stayed. During the
day some more snow fell from the sky. When I walked home I there was only some
snow left in some small spots.
Watchdog timers are
used in embedded systems to perform a system reset when for some reason the
embedded system is not responding anymore. These are timers that after a
specified time perform some kind of reset operation. To prevent the reset
operation to occur, the timer need to be reset frequently. The ESP32 has several watchdog timers. According to the ESP32-S3 Technical Reference Manual (version 1.6), the watchdog timer in
timer group 0 (belonging to core 0) is automatically enabled during the flash
booting process. In the code of ESP-IDF it is disable again in the function bootloader_config_wdt
when it is no longer needed. The watchdog timer in timer group 0 is enabled
again in call_start_cpu0. No watchdog timer is enable in the function
call_start_cpu1. This means that by default the watchdog timer for
core 1 is not enabled. It is only possible to enabled it by software. If
CONFIG_ESP_INT_WDT is enabled (defined) the watchdog timer in timer
group 1 will be used for Interrupt Watchdog Timer (IWDT). Furthermore, the ESP-IDF also has a
Task Watchdog Timer (TWDT), which is enable with CONFIG_ESP_TASK_WDT_INIT,
that watches the idle task and makes use of the watchdog timer in timer group
0. The idle task has the lowest priority and only becomes active when other
tasks are not active. If the idle tasks is not active, it probably means that
some other task is running all the time. An idle task is started (by default)
on both cores, but it is possible (through setting the field
idle_core_mask to disable the idle tasks to be tracked by task
watchdog timer. The idle tasks are created in the function
prvCreateIdleTasks, which is called from the function
vTaskStartScheduler. Note that there are two definitions of these
function depending on whether FreeRTOS-Kernel-SMP or FreeRTOS-Kernel is used,
which depends on the CONFIG_FREERTOS_SMP define. SMP stands for
Symmetric Multiprocessing, which allows tasks to be scheduled across
multiple identical processor cores. This should not be used when you want to
dedicate one of the cores (core 1 usually) for a dedicated task.
2cm snow and 11.2°C
At the end of the morning, there was about 2cm of snow on the table outside. This means that at least 2cm of snow fell
during the evening and the morning. On ground most of the snow was already
gone. The snow already had changed into rain. Until noon, the temperature at
Twenthe Airport remaind between -0.4 and 0.4° Celcius. It dis not look
like the prediction of 9.4° as the maximum temperature for today was
goint to be reached, but around 3 in the afternoon, the temperature started to
rise and between 6 till the end of the day remained around 11°C with a
maximum of 11.2°C around 11 in the evening. For tomorrow a maximum
temperature of 12.9°C.
I continued my investigation with respect to running 'bare metal' on core 1
of the ESP32. I notice that I was mistaken
about SMP in description about watchdog timers two days ago.
The FreeRTOS SMP scheduling policy means that there is one 'instance' of
the scheduler controlling task on several cores, where with
the AMP scheduling policy each core runs its own 'instance' of FreeRTOS.
The ESP-IDF define CONFIG_FREERTOS_SMP ia about selecting an experimental SMP version of the
FreeRTOS Kernel. The normal kernel verions is SMP capable.
TkkrLab member again
In the past half year, I have been visiting the TkkrLab hackerspace once every while. I have decided to become a member again and
did so this evening.
Some snow
When I was walking to the office, it started to snow.
During the day, there was some snow, from which some did stay on parts of the
ground. Some of it stayed during the evening.
ESP32: Disabling peripheral interrupt source
On October 27, I wrote something about I²C on
the ESP32 without interrupts. I suggested that
idea of disabling interrupt by setting the
INTERRUPT_COREx_SOURCE_y_MAP register to the value 16
(the default). Today, I read in Section 9.3.3.3 of ESP32-S3 Technical Reference Manual that setting the value to 6, 7, 11,
15, 16, or 29 will disable the interrupt source. To disable this, if it was
enabled (for example when calling i2c_new_master_bus), I understand
that you have to execute the following statements:
esp_rom_route_intr_matrix(0, ETS_I2C_EXT0_INTR_SOURCE, 16);
esp_rom_route_intr_matrix(1, ETS_I2C_EXT0_INTR_SOURCE, 16);
The ETS_I2C_EXT0_INTR_SOURCE is found in the SoC specific interrupts.h
file in the soc module.
Prospects & Concepts
Today, I received two Prospects & Concepts catalogues about the
young artist that were supported by the Mondriaan Fonds and exhibited their
works at the Art Rotterdam exhibition. I bought both wooks last Sunday. The
books are:
- Prospects & Concepts edited by Mirjam Beerman, written in
Dutch, and published by Het Mondriaan Fonds in February 2020
from Reread Boeken for € 7.50.
- Prospects & Concepts edited by Mirjam Beerman, written in
Dutch, published by Het Mondriaan Fonds in February 2019
from abcBoekBookBuch for € 7.00.
Fancy Tetris Wooden Puzzle
Some time ago, I found this 'Fancy Tetris Wooden Puzzle' measuring
15×22cm, which is using the same types of pieces as the Chinese Wooden Puzzle. It does not have five pieces of each type, but
only three, except for the yellow and the purple type, which have four pieces
each. Please note that in this puzzle, the colours on the white and purple
types are swapped. The pieces fit in a grid of 8 by 12. Last weekend, I started
a modified version to calculate the number of solutions. The program is still
running and it still might run for some time. Below it shows one solution
where the pieces of the same type are all connected with each other but
minimally touching each other.
Into the city
At Fotogalerie Objektief, I saw the exhibiion
'Gewaande Landschappen' (which in English can be translated as: 'Imagined
Landscapes') with photographs by Hans Bouma. At 14:45, I bought the book De Godenmakers written by
Frank Herbert in
Dutch, translated by Lucien Duzee from the English The Godmakers, published by Het Spectrum in 1994,
ISBN:9789027440457, from Het Goed for
€ 2.60.
This months interesting links
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