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| en:multiasm:paarm:chapter_5_9 [2026/02/27 02:23] – jtokarz | en:multiasm:paarm:chapter_5_9 [2026/05/27 09:51] (current) – [Pulse Width Modulation] ktokarz |
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| The Raspberry Pi has ported out some General-Purpose Input/Output (GPIO) lines. Several lines share functionality across the board's peripherals. To access peripherals like GPIO, they must be enabled in the Raspberry Pi 5 OS. Many things can be done with the Raspberry Pi's available GPIOs. In the picture below, the GPIOs and their alternative functions (in scope) are shown. | The Raspberry Pi has ported out some General-Purpose Input/Output (GPIO) lines. Several lines share functionality across the board's peripherals. To access peripherals like GPIO, they must be enabled in the Raspberry Pi 5 OS. Many things can be done with the Raspberry Pi's available GPIOs. In the picture below, the GPIOs and their alternative functions (in scope) are shown. |
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| {{ :en:multiasm:paarm:2025-12-04_15_54_09-.jpg?600 |}} | {{ :en:multiasm:paarm:2025-12-04_15_54_09-.jpg?600 |40 GPIO Pins Description of Raspberry Pi 5}} |
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| * ''dtparam=uart0=on'' | * ''dtparam=uart0=on'' |
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| There are libraries designed to work with GPIO and/or communication interfaces such as UART, SPI, and I2C. For example, to work with GPIO, a special library in C or Python can be used, or GPIO can be accessed via memory mapping of IO registers. Note that GPIO parameters must be set before using them as outputs or inputs, like setting pull-up or pull-down resistors, setting direction, etc. On Linux, using libraries such as libgpiod or wiringPi/pigpio can save a lot of time. But these libraries are primarily available in C or even higher-level programming languages. The hardest part is to find proper hardware addresses. The Raspberry Pi5 installer RP1 peripheral controller documentation contains two addresses: System-Address, which is 40-bit long, and Proc-Address, which is 32-bit long. Taking the example of peripherals on the APB0 internal bus, the address in Proc-Address is ''0x40000000'', but in System-Address it is ''0x<fc #008000>C0</fc>40000000''. The difference is coloured out. Similar differences appear across all other peripheral buses, and these differences may occur in the code depending on the OS version, installed libraries, and drivers. | There are libraries designed to work with GPIO and/or communication interfaces such as UART, SPI, and I2C. For example, to work with GPIO, a special library in C or Python can be used, or GPIO can be accessed via memory mapping of IO registers. Note that GPIO parameters must be set before using them as outputs or inputs, like setting pull-up or pull-down resistors, setting direction, etc. On Linux-based OS, using libraries such as libgpiod or wiringPi/pigpio can save a lot of time. But these libraries are primarily available in C or even higher-level programming languages. The hardest part is to find proper hardware addresses. The Raspberry Pi5 installer RP1 peripheral controller documentation contains two addresses: System-Address, which is 40-bit long, and Proc-Address, which is 32-bit long. Taking the example of peripherals on the APB0 internal bus, the address in Proc-Address is ''0x40000000'', but in System-Address it is ''0x<fc #008000>C0</fc>40000000''. The difference is coloured out. Similar differences appear across all other peripheral buses, and these differences may occur in the code depending on the OS version, installed libraries, and drivers. |
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| ===== General Purpose Inputs and Outputs (GPIO) ===== | ===== General Purpose Inputs and Outputs (GPIO) ===== |
| Basically, with a single GPIO line, you can do a lot: control almost any hardware, read or take measurements, generate wireless signals, and more. Of course, it is easier to control hardware designed for specific purposes, such as I2C communication in the previously described examples. As with the bit-banging technique, it is possible to generate periodic digital signals and control their duty cycle. | Basically, with a single GPIO line, you can do a lot: control almost any hardware, read or take measurements, generate wireless signals, and more. Of course, it is easier to control hardware designed for specific purposes, such as I2C communication in the previously described examples. As with the bit-banging technique, it is possible to generate periodic digital signals and control their duty cycle. |
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| In Raspberry Pi 5, the RP1 chip documentation contains much more information on pulse-width modulation than on basic communication interfaces. PWM registers are on the internal peripheral bus; the base addresses for PWM0 and PWM1 are ''0x40098000'' and ''0x4009C000'', respectively. This hardware is located in the RP1 chip and accessed through PCIe. The Linux OS sets up hardware address mapping, and this mapping is not exposed as a simple fixed physical address that can be accessed with just ''<fc #800000>LDR</fc>''/''<fc #800000>STR</fc>'' instructions from user space. To access the PWM registers, it is necessary to execute the code at least at the EL1 level and to know already the PCIe mapping, or the mapping can be implemented manually. Again, this is too advanced and carries a risk of breaking something. | In Raspberry Pi 5, the RP1 chip documentation contains much more information on pulse-width modulation than on basic communication interfaces. PWM registers are on the internal peripheral bus; the base addresses for PWM0 and PWM1 are ''0x40098000'' and ''0x4009C000'', respectively. This hardware is located in the RP1 chip and accessed through PCIe. Linux sets up hardware address mapping, and this mapping is not exposed as a simple fixed physical address that can be accessed with just ''<fc #800000>LDR</fc>''/''<fc #800000>STR</fc>'' instructions from user space. To access the PWM registers, it is necessary to execute the code at least at the EL1 level and to know already the PCIe mapping, or the mapping can be implemented manually. Again, this is too advanced and carries a risk of breaking something. |
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| Before proceeding, the base addresses must be checked at least three times (**NO JOKES**) and, if needed, replaced. The PWM0_BASE and IO_BANK0_BASE addresses are already mapped and known for the Raspberry Pi 5. In the example, the GPIO line 18 will be used. | Before proceeding, the base addresses must be checked at least three times (**NO JOKES**) and, if needed, replaced. The PWM0_BASE and IO_BANK0_BASE addresses are already mapped and known for the Raspberry Pi 5. In the example, the GPIO line 18 will be used. |
