Raspberry Pi Pico

[Christian MAUDERER]

Hello,

Raspberry Pi creating their own chips? Sounds like a stupid idea...

Am 21.01.21 um 16:44 schrieb Joel Sherrill:
> Hi
> 
> Is a BSP for this feasible? If it is feasible, is is a GSoC size project?
> 
> It is an M0+ with 264k SRAM. Although I'm not sure what six independent 
> banks does to the amount of RAM for programs?

The SRAM isn't really big. But the STM32F4 is in a similar range. So 
that could work.

> 
> https://www.raspberrypi.org/products/raspberry-pi-pico/ 
> <https://www.raspberrypi.org/products/raspberry-pi-pico/>
> 
> I can see the M0+ support in RTEMS being a broad issue and the memory 
> layout being another but the datasheet seems to show the memory as one 
> block:
> 
> https://datasheets.raspberrypi.org/rp2040/rp2040_datasheet.pdf 
> <https://datasheets.raspberrypi.org/rp2040/rp2040_datasheet.pdf>

Agreed: It seems that the memory can be used in a continuous address 
space so the organization shouldn't matter as long as no performance 
optimization is necessary.


The M0+ could be a real problem. Do we currently have any BSPs for an M0 
or M0+ core? I think adding a new core would be _very_ difficult for a 
GSoC student. Especially I think it's less time this year, isn't it?

By the way: It's a dual core. So if the support is added, it would be 
most likely our smallest SMP system ;-)

> 
> Feature list:
> 
> Dual ARM Cortex-M0+ @ 133MHz
> 264kB on-chip SRAM in six independent banks
> Support for up to 16MB of off-chip Flash memory via dedicated QSPI bus
> DMA controller
> Fully-connected AHB crossbar
> Interpolator and integer divider peripherals
> On-chip programmable LDO to generate core voltage
> 2 on-chip PLLs to generate USB and core clocks
> 30 GPIO pins, 4 of which can be used as analog inputs
> Peripherals
> 2 UARTs
> 2 SPI controllers
> 2 I2C controllers
> 16 PWM channels
> USB 1.1 controller and PHY, with host and device support
> 8 PIO state machines

The chip seems to be thrown together using various IPs (which is not 
necessarily a bad idea if they did it right). UART is an ARM PL011 which 
should be simple - we have already a driver for that. The other 
peripherals seem to be sometimes ARM, sometimes Synopsis, sometimes 
something else. The documentation looks OK on a first glance. So it 
should be doable.

> 
> Not our problem but I don't see obvious details on hooking up a JTAG but 
> if someone does a BSP, that will be an issue.

The chip has a SWCLK and SWDIO. So its not a full JTAG but at least a 
debug interface. The Board has three pins marked "DEBUG" on the small 
side opposite to the USB connector. So in theory a debugger could be 
connected. It even seems that there is an openOCD port done by the 
Raspberry Pi developers:

    https://github.com/raspberrypi/openocd/tree/rp2040

Best regards

Christian

> --joel
> 
> 
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