Datasheet

ACCUM0 = 1234abcd
Nibble 0: 0000000d
Nibble 1: 000000c0
Nibble 2: 00000b00
Nibble 3: 0000a000
Nibble 4: 00040000
Nibble 5: 00300000
Nibble 6: 02000000
Nibble 7: 10000000
Masking with sign extension:
Nibble 0: fffffffd
Nibble 1: ffffffc0
Nibble 2: fffffb00
Nibble 3: ffffa000
Nibble 4: 00040000
Nibble 5: 00300000
Nibble 6: 02000000
Nibble 7: 10000000
Changing the result and input multiplexers can create feedback between the accumulators. This is useful e.g. for audio
dithering.
Pico Examples: https://github.com/raspberrypi/pico-examples/tree/pre_release/interp/hello_interp/hello_interp.c Lines 48 - 63
48 void cross_lanes() {
49 interp_config cfg = interp_default_config();
50 interp_config_cross_result(&cfg, true);
51 // ACCUM0 gets lane 1 result:
52 interp_set_config(interp0, 0, &cfg);
53 // ACCUM1 gets lane 0 result:
54 interp_set_config(interp0, 1, &cfg);
55
56 interp0->accum[0] = 123;
57 interp0->accum[1] = 456;
58 interp0->base[0] = 1;
59 interp0->base[1] = 0;
60 puts("Lane result crossover:");
61 for (int i = 0; i < 10; ++i)
62 printf("PEEK0, POP1: %d, %d\n", interp0->peek[0], interp0->pop[1]);
63 }
This should print:
PEEK0, POP1: 124, 456
PEEK0, POP1: 457, 124
PEEK0, POP1: 125, 457
PEEK0, POP1: 458, 125
PEEK0, POP1: 126, 458
PEEK0, POP1: 459, 126
PEEK0, POP1: 127, 459
PEEK0, POP1: 460, 127
PEEK0, POP1: 128, 460
PEEK0, POP1: 461, 128
RP2040 Datasheet
2.3. Processor subsystem 39