Device Debug Print

Note

Tools are only fully supported on source builds.

Overview

The device can optionally print to the host terminal or a log file. This feature can be useful for printing variables, addresses, and Circular Buffer data from kernels running on the device. Device-side prints are controlled through API calls; the host-side is controlled through environment variables.

Enabling

Device debug printing can be enabled and configured using the environment variables shown below. The first environment variable, TT_METAL_DPRINT_CORES specifies which cores the host-side will read print data from, and whether this environment variable is defined determines whether printing is enabled during kernel compilation. Note that the core coordinates are logical coordinates, so worker cores and ethernet cores both start at (0, 0).

export TT_METAL_DPRINT_CORES=0,0                    # required, x,y OR (x1,y1),(x2,y2),(x3,y3) OR (x1,y1)-(x2,y2) OR all OR worker OR dispatch
export TT_METAL_DPRINT_ETH_CORES=0,0                # optional, x,y OR (x1,y1),(x2,y2),(x3,y3) OR (x1,y1)-(x2,y2) OR all OR worker OR dispatch
export TT_METAL_DPRINT_CHIPS=0                      # optional, comma separated list of chips OR all. Default is all. Mutually exclusive with TT_METAL_DPRINT_NODES and TT_METAL_DPRINT_MESH_COORDS.
export TT_METAL_DPRINT_NODES="(M0,D0),(M0,D1)"      # optional, comma separated list of `FabricNodeId` nodes (unique node identifiers in format (Mn,Dn), where M is mesh ID and D is device ID) OR all. Default is all. Mutually exclusive with TT_METAL_DPRINT_CHIPS and TT_METAL_DPRINT_MESH_COORDS.
export TT_METAL_DPRINT_MESH_COORDS="(0,0),(1,3)"    # optional, comma separated list of (row,col) coordinates in the global system mesh OR all. Default is all. Mutually exclusive with TT_METAL_DPRINT_CHIPS and TT_METAL_DPRINT_NODES.
export TT_METAL_DPRINT_RISCVS=BR                    # optional, default is all RISCs. Use a subset of BR,NC,TR0,TR1,TR2,TR*,ER0,ER1,ER*
export TT_METAL_DPRINT_FILE=log.txt                 # optional, default is to print to the screen
export TT_METAL_DPRINT_PREPEND_DEVICE_CORE_RISC=0   # optional, enabled by default. Prepends prints with <device id>:(<core x>, <core y>):<RISC>:.
export TT_METAL_DPRINT_ONE_FILE_PER_RISC=1          # optional, splits DPRINT data on a per-RISC basis into files under $TT_METAL_HOME/generated/dprint/. Overrides TT_METAL_DPRINT_FILE and disables TT_METAL_DPRINT_PREPEND_DEVICE_CORE_RISC.

To generate device debug prints on the device, include the api/debug/dprint.h header and use the APIs defined there. An example with the different features available is shown below:

Important

Each DPRINT line must end with \n. The host-side print server flushes its per-RISC intermediate buffer only when it sees a newline; messages without one are buffered until a later print supplies a \n, and any tail still buffered at device detach is dropped (it is not flushed on device close). If your prints never appear, the most common cause is a missing \n.

Examples: 1. DPRINT("hit checkpoint {}\n", id); // This will be printed 2. DPRINT("hit checkpoint {}", id); // This may never be printed

#include "api/debug/dprint.h"  // required in all kernels using DPRINT

enum TestEnum { VAL0, VAL1, VAL2 };

void kernel_main() {
    // Supported scalar types: bool (prints false/true), char, all fixed-width integer types
    // (uint8_t-uint64_t, int8_t-int64_t), float, and double.
    DPRINT("Test string {} {} {}\n", 'a', 5, 0.123456f);
    // bool prints as false or true
    bool flag = true;
    DPRINT("Bool value: {}\n", flag);  // prints: Bool value: true
    // BF16 type printing is supported via provided type
    bf16_t my_bf16_val(0x3dfb); // Equivalent to 0.122559
    DPRINT("BF16 value: {}\n", my_bf16_val);

    // DPRINT supports formatting options that are supported by fmtlib:
    DPRINT("{:.5f}\n", 0.123456f);
    DPRINT("{:>10}\n", 123); // right align in a field of width 10
    DPRINT("{:<10}\n", 123); // left align in a field of width 10
    DPRINT("{0:x} {0} {0:o} {0:b}\n", 15); // single argument print in hexadecimal, decimal, octal, and binary

    // The following prints only occur on a particular RISCV core:
    DPRINT_MATH("this is the math kernel\n");
    DPRINT_PACK("this is the pack kernel\n");
    DPRINT_UNPACK("this is the unpack kernel\n");
    DPRINT_DATA0("this is the data movement kernel on noc 0\n");
    DPRINT_DATA1("this is the data movement kernel on noc 1\n");
}

Strings

Runtime const char* pointers are printed as hex addresses since the host cannot read device memory. To print the actual string content, use CTSTR() which stores the string in the ELF at compile time so the host can resolve it:

const char* s = "Hello world!";
DPRINT("Pointer: {}\n", s);               // prints: Pointer: 0x12345678
DPRINT("String: {}\n", CTSTR("Hello!"));  // prints: String: Hello!

Enums

Enum types are supported natively. When DWARF debug info is present in the ELF, enum values are printed as their symbolic names. Use {:#} to include the fully-qualified type name:

enum class Color : uint8_t { Red = 0, Green = 1, Blue = 2 };
DPRINT("Color: {}\n", Color::Green);    // prints: Color: Green
DPRINT("Color: {:#}\n", Color::Blue);   // prints: Color: Color::Blue

Flag enums (with operator|) are detected at compile time and printed with | separators:

enum class Flags : uint32_t { A = 1, B = 2, C = 4 };
constexpr Flags operator|(Flags a, Flags b) {
    return static_cast<Flags>(static_cast<uint32_t>(a) | static_cast<uint32_t>(b));
}
DPRINT("Flags: {}\n", Flags::A | Flags::C);    // prints: Flags: A | C
DPRINT("Flags: {:#}\n", Flags::A | Flags::C);  // prints: Flags: Flags::A | Flags::C

If no DWARF debug info is available, enum values are printed as (TypeName)integer.

Circular Buffers

Data from Circular Buffers can be printed using the TileSlice object. It can be constructed as described below, and fed directly to a DPRINT call.

Argument	Type	Description
cb_id	uint8_t	Id of the Circular Buffer to print data from.
tile_idx	int	Index of tile inside the CB to print data from.
slice_range	SliceRange	A struct to describe starting index, ending index, and stride for data to print within the CB. Fields are h0, h1, hs, w0, w1, ws, all uint8_t.
cb_type	dprint_tslice_cb_t	Only used for Data Movement RISCs, specify TSLICE_INPUT_CB or TSLICE_OUTPUT_CB depending on if the CB to print from is input or output.
ptr_type	dprint_tslice_ptr_t	Only used for Data Movement RISCs, specify TSLICE_RD_PTR to read from the front of the CB, or TSLICE_WR_PTR to read from the back of the CB. UNPACK RISC only reads from the front of the CB, PACK RISC only reads from the back of the CB.
endl_rows	bool	Whether to add a newline between printed rows, default true.
print_untilized	bool	Whether to untilize the CB data while printing it (always done for block float formats), default true.

An example of how to print data from a CB (in this case, CBIndex::c_25) is shown below. Note that sampling happens relative to the current CB read or write pointer. This means that for printing a tile read from the front of the CB, the DPRINT call has to occur between the cb_wait_front and cb_pop_front calls. For printing a tile from the back of the CB, the DPRINT call has to occur between the cb_reserve_back and cb_push_back calls. Currently supported data formats for printing from CBs are DataFormat::Float32, DataFormat::Float16_b, DataFormat::Bfp8_b, DataFormat::Bfp4_b, DataFormat::Int8, DataFormat::UInt8, DataFormat::UInt16, DataFormat::Int32, and DataFormat::UInt32.

#include "api/debug/dprint.h"  // required in all kernels using DPRINT

void kernel_main() {
    // Assuming the tile we want to print from CBIndex::c_25 is from the front the CB, print must happen after
    // this call. If the tile is from the back of the CB, then print must happen after cb_reserve_back().
    cb_wait_front(CBIndex::c_25, 1);
    ...

    // Extract a numpy slice `[0:32:16, 0:32:16]` from tile `0` from `CBIndex::c_25` and print it.
    DPRINT("{}\n", TSLICE(CBIndex::c_25, 0, SliceRange::hw0_32_16()));
    // Note that since the MATH core does not have access to CBs, so this is an invalid print:
    DPRINT_MATH("{}\n", TSLICE(CBIndex::c_25, 0, SliceRange::hw0_32_16())); // Invalid

    // Print a full tile
    for (int32_t r = 0; r < 32; ++r) {
        SliceRange sr = SliceRange{.h0 = r, .h1 = r+1, .hs = 1, .w0 = 0, .w1 = 32, .ws = 1};
        // On data movement RISCs, tiles can be printed from either the CB read or write pointers. Also need to specify whether
        // the CB is input or output.
        DPRINT_DATA0("{} --READ--cin1-- {}\n", (uint)r, TileSlice(0, 0, sr, TSLICE_INPUT_CB, TSLICE_RD_PTR, true, false));
        DPRINT_DATA1("{} --READ--cin1-- {}\n", (uint)r, TileSlice(0, 0, sr, TSLICE_OUTPUT_CB, TSLICE_WR_PTR, true, false));
        // Unpacker RISC only has rd_ptr and only input CBs, so no extra args
        DPRINT_UNPACK("{} --READ--cin1-- {}\n", (uint)r, TileSlice(0, 0, sr, true, false));
        // Packer RISC only has wr_ptr
        DPRINT_PACK("{} --READ--cin1-- {}\n", (uint)r, TileSlice(0, 0, sr, true, false));
    }

    ...
    cb_pop_front(CBIndex::c_25, 1);
}

Note

The host-side DPRINT server splits each per-RISC stream on the newline character \n. Anything written without a trailing \n is held in an intermediate buffer until a later print provides one. If a kernel never emits a final \n, the trailing partial line is not flushed when the device is closed and will be lost. Always terminate DPRINT format strings with \n.