I thought the book I'm reading had typos when I read code that uses this:

uint32_t src = 0xf0;
uint32_t dest = 0x400;

int main() {
    *&dest = *&src;
}

However if you take a look at the decompiled version on godbolt: link this correctly takes the value at the address stored in src, and copies it to the address in dest.

I'd love some help understanding what going on. The code looks like nonsense to me, "*&" should "cancel out" IMO.

========

Meanwhile here's what I thought the correct code would be:

uint32_t src = 0xf0;
uint32_t dest = 0x400;

int main() {
    *(uint32_t*) dest = *(uint32_t*) src;
}

Doesn't do what's expected, see decompiled: link. What's wrong with this?

When the RHS is a constant it works fine, and seems to be a common pattern people use.

I'm trying to write a linker file to get C code running on a risc-v MCU (using riscv64-unknown-elf toolchain). My linker script looks like this, simplified:

MEMORY {
        IRAM (rx) : ORIGIN = 0x00000000, LENGTH = 1024
}

ENTRY(_start)

SECTIONS {
    .text : ALIGN(4) {
        *(.text)
    } >IRAM

...

readelf -h correctly shows the entry point's address to be the same as where _start is in the output executable. But I want _start to be at 0x0, not somewhere else, so that when I objcopy it to a flat binary, the start code will be at the beginning. How can I do this?

Right now I'm having the _start function go in a new section called ".boot" I've defined in the C file using __attribute__((section(".boot"))), then, placing this at the start of .text in the linker script like so

...
    .text : ALIGN(4) {
        *(.boot)
        *(.text)
...

But IDK if this how it should be done.

Thanks in advance :)

Im working on a board for controlling a few linear actuators. They will at full load draw something like 10A, and will be powered by a 24V (or so) LiPo pack.

I have a few H-bridges and as expected when the power is cut off, there is an inductive kickback of about 10A. No PWM, they will be turned on and off occasionally only.

I havent been able to fibd anything on if a LiPo pack would be able to take this reverse current, or if it needs some sort of protection. It also lasts for quite a short time but I'm new to batteries so I want to be sure its not a problem.

Would apprecaite any help :)

This is from a section on why decoupling capacitors should be attached to CMOS chips. It shows current spikes during transitions. Which then because of the inductance of traces connecting power to the chip, will cause the power rail voltage to droop.

But why is the ground voltage also shown to rise? What does it even mean for ground voltage to rise when ground is what voltage is measured against?

I'm using an Arduino and through a library working with an IC (MCP2515, a CAN controller) over SPI. The IC indicates interrupts by causing a falling edge on an interrupt pin.

Components are connected using jumper wires on a breadboard.

• When a logic analyzer is not attached, the IRQ gets called a few hundred times. It should only be called once. I thought it must be noise on the external interrupt pin but a pull-up doesn't help. I've tried the internal pullup and an external one.
• Trying to see if there is a ton of interrupts from the IC, or an error internal to the Arduino, I attach my logic analyzer. Now it works perfect.

Any idea what might cause such a weird issue? Looking around I haven't found anything.

EDIT: I found a Reddit post for a different circuit where a user suggested placing a small capacitor to make the edges of a signal rise slower. This has fixed my problem.

Since I've already created a post: does anyone know why I was getting an unending number of interrupts? Why would the edges of the interrupt signal changing too fast cause something like this?

Not sure if this is a dumb question but this has me quite puzzled.

The legs on TO220 packages are very small. How is it that there are e.g MOSFETS rated as being able to continuously conduct ~100A? e.g IRF1404Z

From what I understand such large currents need busbars on PCBs and these appear a lot larger than the legs on these components.

I'm making a driver for a small 15V, hall sensored, 9-slot BLDC motor I got off of AliExpress. It has u,v,w inputs. Three hall outputs and Vcc, Gnd for them. No datasheet :)

I understand the working principle: I'll have to use the hall sensors to figure out the location of the rotor, then power the appropriate windings.

Trouble is, I don't know how the windings for the three phases are arranged within the motor. So I don't know which pin to give power to, because I don't know which windings within the motor will then be powered.

How can I figure out where the windings are for each phase?

I'm guessing I've got to manually spin the motor and do some detective work with back-emf measurements and hall sensor outputs to figure this out?