SWO Output

Basic SWO Output Configuration

Simple SWO ascii console, CPU running at 72MHz, SWO at 2MHz, SWO data comes from probe itself (eg. ST-LINK)

"swoConfig":{
    "enabled":true,
    "source":"probe",
    "swoFrequency": 2000000,
    "cpuFrequency":72000000,
    "decoders": [
        {
            "port": 0,
            "type": "console",
            "label": "SWO output",
            "encoding":"ascii"
        }
    ]
}

ARM basic config

This example expects CMSIS usage

Init

/* Select the SWO interface */
DBGMCU->CR &= DBGMCU_CR_TRACE_MODE_Msk;

/* Enable the TRACE interface */
DBGMCU->CR |= DBGMCU_CR_TRACE_IOEN;

Send character

ITM_SendChar(character);

Note: Don't forget to properly configure SWO pin.

Advanced Decoder Creation

Output Graphing

Example of a time series graph with two lines

VSCode Cortex Debug configuration

"type": "cortex-debug",
            "request": "attach",
            "servertype": "openocd",
            "cwd": "${workspaceRoot}/build",
            "executable": "NucleoProject.elf",
            "name": "Debug (OpenOCD)",
            "device": "STM32F303",
            "svdFile": "../scripts/openOCD/STM32F303.svd",  // from Google search
            "showDevDebugOutput": false,
            "configFiles": [
                "board/st_nucleo_f3.cfg"    // OpenOCD board configuration (in the OpenOCD/scripts folder)
            ],
            "swoConfig": 
            {
                "enabled": true, 
                "decoders": [
                    {
                        "type": "graph",
                        "port": 0,      // ITM (Instrumentation Trace Macrocell) stimulus port
                        "encoding": "unsigned",
                        "graphId": "1", // ID of the corresponding graph plot
                        "scale": 1
                    },
                    {
                        "type": "graph",
                        "port": 1,      // ITM (Instrumentation Trace Macrocell) stimulus port
                        "encoding": "unsigned",
                        "graphId": "2", // ID of the corresponding graph plot
                        "scale": 1
                    },
                ],
                "cpuFrequency": 75000000,   // Configured CPU speed
                "swoFrequency":  2000000,   // Maximum speed of ST-Link/V2
                "source": "probe",
            },
            "graphConfig": [
                {
                    "label": "Graph 1",
                    "timespan": 5,
                    "type": "realtime",
                    "annotate": false,
                    "maximum": 256,
                    "minimum": 0,
                    "plots": [
                        {
                            "graphId": "1", // ID as reference for a decoder
                            "label": "data 1",
                            "color": "#53753c"
                        },
                        {
                            "graphId": "2", // ID as reference for a decoder
                            "label": "data 2",
                            "color": "#955f20"
                        }
                    ]
                },
            ]
        },

Modified ITM_SendChar (CMSIS) function (added ITM port)

uint8_t ITM_SendChar(uint8_t ch, size_t const port)
{
  if (((ITM->TCR & ITM_TCR_ITMENA_Msk) != 0UL) &&      /* ITM enabled */
      ((ITM->TER & (port+1)          ) != 0UL)   )     /* ITM Port enabled */
  {
    while (ITM->PORT[port].u32 == 0UL)
    {
      __NOP();
    }
    ITM->PORT[port].u8 = (uint8_t)ch;
   }
  return (ch);
}

VSCode Cortex Debug output graph

Note that the maximum stable data rate with ST-Link/V2 is about 8kiB/s, the implementation of the Graph however does limit the data rate even further. The graph will skip samples, if the data rate is too high.