Contents
Is reset needed for SWD?
Reset is not mandatory either in JTAG or SWD but it’s recommended that you make it available anyway. If you don’t have spare pins in the debug connector then I would at least make it available as a test point.
What is SWD pin?
Serial Wire Debug (SWD) is a 2-pin (SWDIO/SWCLK) electrical alternative JTAG interface that has the same JTAG protocol on top. This enables the debugger to become another AMBA bus master for access to system memory and peripheral or debug registers. The Debug Access Port (DAP) is split into two main control units.
What is Swo in SWD?
SWO specifies a dedicated pin, in addition to the debug signals of the SWD interface, which allows the target CPU to output specific data like printf output on a dedicated pin via UART or Manchester protocol. This pin is unidirectional, so it is not possible to send data to the target CPU on this pin.
What is NRST stm32?
In short, NRST pin is used to activate bootloader when you need to flash new program using one of the communication channels and to reset MCU to default state when you want to flash new program using SWD interface and SWD pins are not available.
What is RCC in MCU?
The RCC peripheral is used to control the internal peripherals, as well as the reset signals and clock distribution. The RCC gets several internal (LSI, HSI and CSI) and external (LSE and HSE) clocks.
Which is the RESET pin on a SWD switch?
There is usually a dedicated pin for the reset, most of the times labelled nRST. In order to connect to the DP, the debugging interface must pull the nRST low, then issue the JTAG->SWD switch command. A J-Link interface is able to handle such a chip, and it was just a matter of connecting the nRST pin of the chip to the RESET pin of the J-Link.
Do you need RST pin for SWD interface?
No – it is not necessary to connect the nRESET pin to the RESET pin on the nRF52 chip. The nRF51 had a SWD protocol that was not standard – the reset was multiplexed on the SWDIO lines. This is not the…
How does a SWD switch connect to a DP?
In order to connect to the DP, the debugging interface must pull the nRST low, then issue the JTAG->SWD switch command. A J-Link interface is able to handle such a chip, and it was just a matter of connecting the nRST pin of the chip to the RESET pin of the J-Link. The same is possible using an official ST-Link interface as well.
How does the SWD interface work with the CPU?
In addition to the debug signals, ARM’s SWD interface also specifies a dedicated pin which allows the target CPU to output specific data like printf output on a dedicates pin via UART or Manchester protocol. This pin is unidirectional, so it is not possible to send data to the target CPU on this pin.