Now do the same with the measure clock frequencies 1.85/2.94 or approximately 0.629. Looking at the numbers, if we divide the clock frequencies we have 250/400 or a 0.625. Why does the SPI clock work as expected if the core clock is under clocked to 250 MHz? This time, Figure 2 shows the clock frequency is much better at 2.94 MHz. With the device tree updated, the same simple SPI test program is run again at 3MHz. This is a simple program which increments a number, sends it out the SPI port and then loops.įigure 2 SPI Clock and MOSI lines on the Pi 3 CM showing expected clock frequency Now that we have determined what the clock speeds are, let’s take a look at sending some data over the SPI. We can also see that the Pi 1 and Pi 2 have a default clock speed of 250 MHz, whereas the Pi 3 and Pi Zero have a default clock speed of 400 MHz. If we take a look at the clock descriptions on, we can see that the Pi’s GPU frequency is used to set the core frequency which trickles down to setting the serial communication clocks such as the UARTs and SPI. Each generation of the Pi, from 0 to 3, has variations in hardware, specs and clock speeds. The original Pi has been revised multiple times with the latest being the Raspberry Pi 3 Model B. This blog will focus on an interesting finding in the core clock speed for the Raspberry Pi 3 Compute module (CM) and the default Raspbian image. The Raspberry Pi was originally designed to teach computer science, but has taken off in the open source community as an easy to use and well supported SBC. Tristan Nixon in Engineering, Product Development | No comments Understanding the Raspberry Pi Clock Conundrum We often see the Raspberry Pi being designed in medical devices as a cost effective Single Board Computer (SBC).
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