Raspberry Pi Pico Micropython PWM DMA RING LED fade

Pico_DMA_RING_PWM_LED_fade.py

from uctypes import *
from machine import Pin, PWM, mem32

# control register structure
DMA_CTRL_LAYOUT = {
    "AHB_ERROR":    31<<BF_POS | 1<<BF_LEN | BFUINT32,
    "READ_ERROR":   30<<BF_POS | 1<<BF_LEN | BFUINT32,
    "WRITE_ERROR":  29<<BF_POS | 1<<BF_LEN | BFUINT32,
    "BUSY":         24<<BF_POS | 1<<BF_LEN | BFUINT32,
    "SNIFF_EN":     23<<BF_POS | 1<<BF_LEN | BFUINT32,
    "BSWAP":        22<<BF_POS | 1<<BF_LEN | BFUINT32,
    "IRQ_QUIET":    21<<BF_POS | 1<<BF_LEN | BFUINT32,
    "TREQ_SEL":     15<<BF_POS | 6<<BF_LEN | BFUINT32,
    "CHAIN_TO":     11<<BF_POS | 4<<BF_LEN | BFUINT32,
    "RING_SEL":     10<<BF_POS | 1<<BF_LEN | BFUINT32,
    "RING_SIZE":     6<<BF_POS | 4<<BF_LEN | BFUINT32,
    "INCR_WRITE":    5<<BF_POS | 1<<BF_LEN | BFUINT32,
    "INCR_READ":     4<<BF_POS | 1<<BF_LEN | BFUINT32,
    "DATA_SIZE":     2<<BF_POS | 2<<BF_LEN | BFUINT32,
    "HIGH_PRIORITY": 1<<BF_POS | 1<<BF_LEN | BFUINT32,
    "EN":            0<<BF_POS | 1<<BF_LEN | BFUINT32
}


DMA_BASE = const(0x5000_0000)

# channel offset
DMA_CH = 0x040

# alias CSRs offset address
DMA_0_READ_ADDR   = const(0x000)
DMA_0_WRITE_ADDR  = const(0x004)
DMA_0_TRANS_COUNT = const(0x008)
DMA_0_CTRL_TRIG   = const(0x00c)
DMA_1_TRANS_COUNT_TRIG = const(0x01c)
DMA_3_TRANS_COUNT_READ_ADD_TRIG = const(0x038)

# raw intrrupt status register
DMA_INTR = const(0x400)


PWM_BASE = const(0x4005_0000)

#channel offset  (PWM_BASE + (CH * ch) + CC)
PWM_CH = const(0x14)

PWM_CSR = const(0x00) # control and status register
PWM_DIV = const(0x04) # divider
PWM_CTR = const(0x08) # counter
PWM_CC  = const(0x0c) # counter compare
PWM_TOP = const(0x10) # counter wrap value

@micropython.viper
def fade():
    buff = bytes(4 * 256 * 2)
    base = int(ptr(buff))
    for i in range(4 * 256):
        addr = base + i
        if (addr & 0b11_1111_1111) == 0:
            break
    
    for i in range(0, 256 * 4, 4):
        j = i //4
        machine.mem32[addr + i] = uint(j * j << 16)
    return buff, addr
    
fade, fade_addr = fade()


# pwm slice 4
DREQ_PWM_WRAP4 = 28
pwm_ch = PWM_BASE + (PWM_CH * 4)
pwm_cc = pwm_ch + PWM_CC


# PWM slice=4, channel=1
led = PWM(Pin(25))
# clkdiv 8.0
mem32[pwm_ch + PWM_DIV] = (0x8 << 4)
# start pwm
mem32[pwm_ch + PWM_CSR] |= 1


dma_ch = DMA_BASE + (DMA_CH * 2)
ctrl = struct(dma_ch + DMA_0_CTRL_TRIG, DMA_CTRL_LAYOUT)
ctrl.EN = 0

mem32[dma_ch + DMA_0_READ_ADDR] = fade_addr
mem32[dma_ch + DMA_0_WRITE_ADDR] = pwm_cc
mem32[dma_ch + DMA_0_TRANS_COUNT] = 256 * 5 # n * 4 bytes

ctrl.TREQ_SEL = DREQ_PWM_WRAP4
ctrl.CHAIN_TO = 2
ctrl.INCR_WRITE = 0
ctrl.INCR_READ = 1
ctrl.DATA_SIZE = 0x2 # SIZE_WORD: 4 bytes

#ctrl.RING_SEL = 0 # read
ctrl.RING_SIZE = 10

ctrl.EN = 1