From d69cc9fcaa8d4183284e546c34be54def0a0ceda Mon Sep 17 00:00:00 2001
From: Peter Hinch <peter@hinch.me.uk>
Date: Sat, 12 Jul 2025 18:04:29 +0100
Subject: [PATCH] Update spi_dma.py

---
 temp/spi_dma.py | 118 +++++++++++++++++++++++++++++-------------------
 1 file changed, 72 insertions(+), 46 deletions(-)

diff --git a/temp/spi_dma.py b/temp/spi_dma.py
index 8d2a110..f486efc 100644
--- a/temp/spi_dma.py
+++ b/temp/spi_dma.py
@@ -1,65 +1,91 @@
 # Derived from https://github.com/raspberrypi/pico-micropython-examples/blob/master/pio/pio_spi.py
 import rp2
 from machine import Pin
-import time
+import asyncio
+from micropython import alloc_emergency_exception_buf
 
-# ***** 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)
+alloc_emergency_exception_buf(100)
 
-# ***** 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)
+@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]
+    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)[1]
+    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
+    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
+# Get data request channel for a SM: RP2040 datasheet 2.5.3 RP2350 12.6.4.1
+def dreq(sm, rx=False):
+    d = (sm & 3) + ((sm >> 2) << 3)
+    return 4 + d if rx else d
+
+
+class RP2_SPI_DMA_MASTER:
+    def __init__(self, sm_num, freq, sck, mosi, callback):
+        self._sm_num = sm_num
+        self._dma = rp2.DMA()
+        self._dma.irq(handler=callback, hard=True)  # Assign callback
+        dc = dreq(sm_num)  # Data request channel
+        # Transfer bytes, don't increment the write address, irq at end, and pace the transfer.
+        self._ctrl = self._dma.pack_ctrl(size=0, inc_write=False, irq_quiet=False, treq_sel=dc)
+        f = 4 * freq  # 4 clock cycles per bit
+        self._sm = rp2.StateMachine(sm_num, spi_cpha0, freq=f, sideset_base=sck, out_base=mosi)
+        self._sm.active(1)
+
+    def close(self):
+        self._dma.active(0)
+        self._sm.active(0)
+
+    def write(self, data):
+        self._dma.config(read=data, write=self._sm, count=len(data), ctrl=self._ctrl, trigger=True)
 
-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
+pin_cs = Pin(20, Pin.OUT, value=1)
+pin_sck = Pin(18, Pin.OUT, value=0)
+pin_mosi = Pin(19, Pin.OUT, value=0)
+
+tsf = asyncio.ThreadSafeFlag()
+
+
+def callback(dma):  # Hard ISR
+    tsf.set()  # Flag user code that transfer is complete
+
+
+spi = RP2_SPI_DMA_MASTER(0, 1_000_000, pin_sck, pin_mosi, callback)
+
+
+async def eot():  # Handle end of transfer
+    while True:
+        await tsf.wait()
+        pin_cs(1)
+
+
+async def main():
+    src_data = b"the quick brown fox jumps over the lazy dog"
+    asyncio.create_task(eot())
+    n = 0
+    while True:
+        pin_cs(0)
+        spi.write(src_data)  # "Immediate" return.
+        await asyncio.sleep(1)
+        print(n)
+        n += 1
+
+
+try:
+    asyncio.run(main())
+except KeyboardInterrupt:
+    spi.close()
+    asyncio.new_event_loop()