Add spi_dma demo.

temp/spi_dma.py

@@ -0,0 +1,65 @@
+# Derived from https://github.com/raspberrypi/pico-micropython-examples/blob/master/pio/pio_spi.py
+import rp2
+from machine import Pin
+import time
+
+# ***** Define connfiguration *****
+sm_num = 0
+pio_num = 0
+freq = 1_000_000
+pincs = Pin(20, Pin.OUT)
+pin_sck = Pin(18)
+pin_mosi = Pin(19)
+
+# ***** Transfer complete callback *****
+def callback(dma):
+    pincs(1)
+    # Flag user code that transfer is complete
+
+# *****
+
+@rp2.asm_pio(autopull=True, pull_thresh=8, sideset_init=(rp2.PIO.OUT_LOW,), out_init=rp2.PIO.OUT_LOW)
+def spi_cpha0():
+    # Note X must be preinitialised by setup code before first byte, we reload after sending each byte
+    set(x, 6)
+    # Actual program body follows
+    wrap_target()
+    pull(ifempty)            .side(0x0)   [1]
+    label("bitloop")
+    out(pins, 1)             .side(0x0)   [1]
+    #mov(y, y)                .side(0x1)
+    jmp(x_dec, "bitloop")    .side(0x1)   [1]
+
+    out(pins, 1)             .side(0x0)
+    set(x, 6)                .side(0x0)
+    mov(y, y)                .side(0x1)  # NOP
+    jmp(not_osre, "bitloop") .side(0x1)  # Fallthru if TXFIFO empties
+    wrap()
+
+piospi_sm = rp2.StateMachine(sm_num, spi_cpha0, freq=4*freq, sideset_base=pin_sck, out_base=pin_mosi)
+piospi_sm.active(1)
+
+DATA_REQUEST_INDEX = (pio_num << 3) + sm_num
+
+d = rp2.DMA()
+d.irq(handler=callback, hard=True)  # Assign callback
+# Transfer bytes, rather than words, don't increment the write address, irq at end, and pace the transfer.
+c = d.pack_ctrl(size=0, inc_write=False, irq_quiet=False, treq_sel=DATA_REQUEST_INDEX)
+def send(data):
+    pincs(0)  # Assert CS/
+    d.config(
+        read=data,
+        write=piospi_sm,
+        count=len(data),
+        ctrl=c,
+        trigger=True
+    )
+
+# ***** Test Script *****
+n = 0
+while True:
+    src_data = b'the quick brown fox jumps over the lazy dog'
+    send(src_data)  # "Immediate" return.
+    time.sleep(1)
+    print(n)
+    n += 1