stm32: Add implementation of machine.bitstream.

Hand-written version for M0, and cycle-counter version for everything else.

Signed-off-by: Jim Mussared <jim.mussared@gmail.com>

ports/stm32/Makefile

@@ -318,6 +318,7 @@ SRC_C += \
 	gccollect.c \
 	help.c \
 	machine_adc.c \
+	machine_bitstream.c \
 	machine_i2c.c \
 	machine_i2s.c \
 	machine_spi.c \

ports/stm32/boards/NUCLEO_L073RZ/mpconfigboard.h

@@ -19,6 +19,8 @@
 #define MICROPY_PY_UHEAPQ           (0)
 #define MICROPY_PY_UTIMEQ           (0)
 
+#define MICROPY_PY_MACHINE_BITSTREAM (0)
+
 #define MICROPY_HW_ENABLE_INTERNAL_FLASH_STORAGE (0)
 #define MICROPY_HW_ENABLE_RTC       (1)
 #define MICROPY_HW_ENABLE_ADC       (0)

ports/stm32/machine_bitstream.c

@@ -0,0 +1,204 @@
+/*
+ * This file is part of the MicroPython project, http://micropython.org/
+ *
+ * The MIT License (MIT)
+ *
+ * Copyright (c) 2021 Jim Mussared
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+
+#include "py/runtime.h"
+#include "py/mphal.h"
+#include "extmod/machine_bitstream.h"
+
+#if MICROPY_PY_MACHINE_BITSTREAM
+
+#if __CORTEX_M == 0
+
+// No cycle counter on M0, do manual cycle counting instead.
+
+// STM32F091 @ 48MHz
+#define NS_CYCLES_PER_ITER_HIGH (6)
+#define NS_CYCLES_PER_ITER_LOW (6)
+#define NS_OVERHEAD_CYCLES_HIGH (12)
+#define NS_OVERHEAD_CYCLES_LOW (18)
+
+uint32_t mp_hal_delay_ns_calc(uint32_t ns, bool high) {
+    uint32_t ncycles = SystemCoreClock / 1000000 * ns / 1000;
+    uint32_t overhead = MIN(ncycles, high ? NS_OVERHEAD_CYCLES_HIGH : NS_OVERHEAD_CYCLES_LOW);
+    return MAX(1, MP_ROUND_DIVIDE(ncycles - overhead, high ? NS_CYCLES_PER_ITER_HIGH : NS_CYCLES_PER_ITER_LOW));
+}
+
+void machine_bitstream_high_low(mp_hal_pin_obj_t pin, uint32_t *timing_ns, const uint8_t *buf, size_t len) {
+    const uint32_t high_mask = pin->pin_mask;
+    const uint32_t low_mask = pin->pin_mask << 16;
+    volatile uint32_t *bsrr = &pin->gpio->BSRR;
+
+    // Convert ns to loop iterations [high_time_0, low_time_0, high_time_1, low_time_1].
+    for (size_t i = 0; i < 4; ++i) {
+        timing_ns[i] = mp_hal_delay_ns_calc(timing_ns[i], i % 2 == 0);
+    }
+
+    mp_uint_t atomic_state = MICROPY_BEGIN_ATOMIC_SECTION();
+
+    // Measured timing for F091 at 48MHz (cycle=20.83ns)
+    // timing_ns = (1,1,1,1)
+    //   high: 370
+    //   low:  500
+    //   low8: 660
+    // timing_ns = (2,2,2,2)
+    //   high: 490
+    //   low:  620
+    //   low8: 805
+
+    // --> high is 12 + n*6 cycles
+    //     low is 18 + n*6 cycles
+
+    // NeoPixel timing (400, 850, 800, 450) (+/-150ns) gives timing_ns=(1, 4, 4, 1) which in cycles is
+    // (12 + 6, 18 + 24, 12 + 24, 18 + 6) = (18, 42, 36, 24)
+    // --> (375, 875, 750, 500) nanoseconds.
+    // Measured output on logic analyser is (370, 870, 750, 490) (+/-10ns at 100MHz)
+
+    // Note: final low of LSB is longer by 8 cycles (160ns) (due to start of outer loop and fetching next byte).
+    // This is slightly outside spec, but doesn't seem to cause a problem.
+
+    __asm volatile (
+        // Force consistent register assignment.
+        // r6 = len
+        "ldr r6, %0\n"
+        // r4 = buf
+        "ldr r4, %1\n"
+        // r5 = timing_ms
+        "ldr r5, %2\n"
+
+        // Must align for consistent timing.
+        ".align 4\n"
+
+        // Don't increment/decrement before first iteration.
+        "b .outer2\n"
+        ".outer:\n"
+        // ++buf, --len
+        "  add r4, #1\n"
+        "  sub r6, #1\n"
+
+        // len iterations
+        ".outer2:\n"
+        "  cmp r6, #0\n"
+        "  beq .done\n"
+
+        // r0 = *buf
+        "  ldrb r0, [r4, #0]\n"
+
+        // 8 bits in byte
+        "  mov r7, #8\n"
+        "  .inner:\n"
+        //   *bsrr = high_mask
+        "    ldr r1, %3\n"
+        "    ldr r2, %4\n"
+        "    str r2, [r1, #0]\n"
+
+        //   r3 = (r0 >> 4) & 8    (r0 is 8 if high bit is 1 else 0)
+        "    mov r8, r6\n"
+        "    lsr r3, r0, #4\n"
+        "    mov r6, #8\n"
+        "    and r3, r6\n"
+        "    mov r6, r8\n"
+
+        //   r2 = timing_ns[r2]
+        "    ldr r2, [r5, r3]\n"
+        "    .loop1:\n sub r2, #1\n bne .loop1\n"
+
+        //   *bsrr = low_mask
+        "    ldr r2, %5\n"
+        "    str r2, [r1, #0]\n"
+
+        //   r2 = timing_ns[r3 + 4]
+        "    add r3, #4\n"
+        "    ldr r2, [r5, r3]\n"
+        "    .loop2:\n sub r2, #1\n bne .loop2\n"
+
+        //   b >>= 1
+        "    lsl r0, r0, #1\n"
+
+        "    sub r7, #1\n"
+        //   end of inner loop
+        "    beq .outer\n"
+        //   continue inner loop
+        "    b .inner\n"
+
+        ".done:\n"
+        :
+        : "m" (len), "m" (buf), "m" (timing_ns), "m" (bsrr), "m" (high_mask), "m" (low_mask)
+        : "r0", "r1", "r2", "r3", "r7", "r8"
+        );
+
+    MICROPY_END_ATOMIC_SECTION(atomic_state);
+}
+
+#else // > CORTEX_M0
+
+// Use cycle counter for timing.
+
+// Measured on PYBV11 at 168MHz & 128MHz and PYBD_SF6 at 128MHz & 144MHz.
+#define NS_CYCLES_OVERHEAD (6)
+
+void machine_bitstream_high_low(mp_hal_pin_obj_t pin, uint32_t *timing_ns, const uint8_t *buf, size_t len) {
+    const uint32_t high_mask = pin->pin_mask;
+    const uint32_t low_mask = pin->pin_mask << 16;
+    volatile uint32_t *bsrr = &pin->gpio->BSRR;
+
+    // Convert ns to cycles [high_time_0, low_time_0, high_time_1, low_time_1].
+    for (size_t i = 0; i < 4; ++i) {
+        timing_ns[i] = SystemCoreClock / 1000000 * timing_ns[i] / 1000;
+        if (timing_ns[i] > NS_CYCLES_OVERHEAD) {
+            timing_ns[i] -= NS_CYCLES_OVERHEAD;
+        }
+        if (i % 2 == 1) {
+            timing_ns[i] += timing_ns[i - 1];
+        }
+    }
+
+    mp_hal_ticks_cpu_enable();
+
+    mp_uint_t atomic_state = MICROPY_BEGIN_ATOMIC_SECTION();
+
+    for (size_t i = 0; i < len; ++i) {
+        uint8_t b = buf[i];
+        for (size_t j = 0; j < 8; ++j) {
+            DWT->CYCCNT = 0;
+            *bsrr = high_mask;
+            uint32_t *t = &timing_ns[b >> 6 & 2];
+            while (DWT->CYCCNT < t[0]) {
+                ;
+            }
+            *bsrr = low_mask;
+            b <<= 1;
+            while (DWT->CYCCNT < t[1]) {
+                ;
+            }
+        }
+    }
+
+    MICROPY_END_ATOMIC_SECTION(atomic_state);
+}
+
+#endif // > CORTEX_M0
+
+#endif // MICROPY_PY_MACHINE_BITSTREAM

ports/stm32/modmachine.c

@@ -33,6 +33,7 @@
 #include "py/objstr.h"
 #include "py/mperrno.h"
 #include "py/mphal.h"
+#include "extmod/machine_bitstream.h"
 #include "extmod/machine_mem.h"
 #include "extmod/machine_signal.h"
 #include "extmod/machine_pulse.h"
@@ -406,6 +407,9 @@ STATIC const mp_rom_map_elem_t machine_module_globals_table[] = {
     { MP_ROM_QSTR(MP_QSTR_disable_irq),         MP_ROM_PTR(&machine_disable_irq_obj) },
     { MP_ROM_QSTR(MP_QSTR_enable_irq),          MP_ROM_PTR(&machine_enable_irq_obj) },
 
+    #if MICROPY_PY_MACHINE_BITSTREAM
+    { MP_ROM_QSTR(MP_QSTR_bitstream),           MP_ROM_PTR(&machine_bitstream_obj) },
+    #endif
     #if MICROPY_PY_MACHINE_PULSE
     { MP_ROM_QSTR(MP_QSTR_time_pulse_us),       MP_ROM_PTR(&machine_time_pulse_us_obj) },
     #endif

ports/stm32/mpconfigport.h

@@ -193,6 +193,9 @@
 #define MICROPY_PY_LWIP_SOCK_RAW    (MICROPY_PY_LWIP)
 #ifndef MICROPY_PY_MACHINE
 #define MICROPY_PY_MACHINE          (1)
+#ifndef MICROPY_PY_MACHINE_BITSTREAM
+#define MICROPY_PY_MACHINE_BITSTREAM (1)
+#endif
 #define MICROPY_PY_MACHINE_PULSE    (1)
 #define MICROPY_PY_MACHINE_PIN_MAKE_NEW mp_pin_make_new
 #define MICROPY_PY_MACHINE_I2C      (1)

py/misc.h

@@ -55,6 +55,7 @@ typedef unsigned int uint;
 
 // Round-up integer division
 #define MP_CEIL_DIVIDE(a, b) (((a) + (b) - 1) / (b))
+#define MP_ROUND_DIVIDE(a, b) (((a) + (b) / 2) / (b))
 
 /** memory allocation ******************************************/