mtm_hardware.dacout: add gain=1 or gain=2 argument

Author: todbot

ports/raspberrypi/boards/mtm_computer/module/DACOut.c

@@ -128,9 +128,19 @@ static const uint16_t mcp4822_pio_program[] = {
 #define MCP4822_CLOCKS_PER_SAMPLE 86
 
 
+// MCP4822 gain bit (bit 13) position in the PIO program:
+//   Instruction 6  = channel A gain bit
+//   Instruction 18 = channel B gain bit
+// 1x gain: set pins, 1 (0xE001) — bit 13 = 1
+// 2x gain: set pins, 0 (0xE000) — bit 13 = 0
+#define MCP4822_PIO_GAIN_INSTR_A 6
+#define MCP4822_PIO_GAIN_INSTR_B 18
+#define MCP4822_PIO_GAIN_1X 0xE001  // set pins, 1
+#define MCP4822_PIO_GAIN_2X 0xE000  // set pins, 0
+
 void common_hal_mtm_hardware_dacout_construct(mtm_hardware_dacout_obj_t *self,
     const mcu_pin_obj_t *clock, const mcu_pin_obj_t *mosi,
-    const mcu_pin_obj_t *cs) {
+    const mcu_pin_obj_t *cs, uint8_t gain) {
 
     // SET pins span from MOSI to CS.  MOSI must have a lower GPIO number
     // than CS, with at most 4 pins between them (SET count max is 5).
@@ -141,14 +151,21 @@ void common_hal_mtm_hardware_dacout_construct(mtm_hardware_dacout_obj_t *self,
 
     uint8_t set_count = cs->number - mosi->number + 1;
 
+    // Build a mutable copy of the PIO program and patch the gain bit
+    uint16_t program[MP_ARRAY_SIZE(mcp4822_pio_program)];
+    memcpy(program, mcp4822_pio_program, sizeof(mcp4822_pio_program));
+    uint16_t gain_instr = (gain == 2) ? MCP4822_PIO_GAIN_2X : MCP4822_PIO_GAIN_1X;
+    program[MCP4822_PIO_GAIN_INSTR_A] = gain_instr;
+    program[MCP4822_PIO_GAIN_INSTR_B] = gain_instr;
+
     // Initial SET pin state: CS high (bit at CS position), others low
     uint32_t cs_bit_position = cs->number - mosi->number;
     pio_pinmask32_t initial_set_state = PIO_PINMASK32_FROM_VALUE(1u << cs_bit_position);
     pio_pinmask32_t initial_set_dir = PIO_PINMASK32_FROM_VALUE((1u << set_count) - 1);
 
     common_hal_rp2pio_statemachine_construct(
         &self->state_machine,
-        mcp4822_pio_program, MP_ARRAY_SIZE(mcp4822_pio_program),
+        program, MP_ARRAY_SIZE(mcp4822_pio_program),
         44100 * MCP4822_CLOCKS_PER_SAMPLE,          // Initial frequency; play() adjusts
         NULL, 0,                                     // No init program
         NULL, 0,                                     // No may_exec

ports/raspberrypi/boards/mtm_computer/module/DACOut.h

@@ -21,7 +21,7 @@ typedef struct {
 
 void common_hal_mtm_hardware_dacout_construct(mtm_hardware_dacout_obj_t *self,
     const mcu_pin_obj_t *clock, const mcu_pin_obj_t *mosi,
-    const mcu_pin_obj_t *cs);
+    const mcu_pin_obj_t *cs, uint8_t gain);
 
 void common_hal_mtm_hardware_dacout_deinit(mtm_hardware_dacout_obj_t *self);
 bool common_hal_mtm_hardware_dacout_deinited(mtm_hardware_dacout_obj_t *self);

ports/raspberrypi/boards/mtm_computer/module/mtm_hardware.c

@@ -29,12 +29,15 @@
 //|         clock: microcontroller.Pin,
 //|         mosi: microcontroller.Pin,
 //|         cs: microcontroller.Pin,
+//|         *,
+//|         gain: int = 1,
 //|     ) -> None:
 //|         """Create a DACOut object associated with the given SPI pins.
 //|
 //|         :param ~microcontroller.Pin clock: The SPI clock (SCK) pin
 //|         :param ~microcontroller.Pin mosi: The SPI data (SDI/MOSI) pin
 //|         :param ~microcontroller.Pin cs: The chip select (CS) pin
+//|         :param int gain: DAC output gain, 1 for 1x (0-2.048V) or 2 for 2x (0-4.096V). Default 1.
 //|
 //|         Simple 8ksps 440 Hz sine wave::
 //|
@@ -72,11 +75,12 @@
 //|         ...
 //|
 static mp_obj_t mtm_hardware_dacout_make_new(const mp_obj_type_t *type, size_t n_args, size_t n_kw, const mp_obj_t *all_args) {
-    enum { ARG_clock, ARG_mosi, ARG_cs };
+    enum { ARG_clock, ARG_mosi, ARG_cs, ARG_gain };
     static const mp_arg_t allowed_args[] = {
         { MP_QSTR_clock, MP_ARG_OBJ | MP_ARG_KW_ONLY | MP_ARG_REQUIRED },
         { MP_QSTR_mosi,  MP_ARG_OBJ | MP_ARG_KW_ONLY | MP_ARG_REQUIRED },
         { MP_QSTR_cs,    MP_ARG_OBJ | MP_ARG_KW_ONLY | MP_ARG_REQUIRED },
+        { MP_QSTR_gain,  MP_ARG_INT | MP_ARG_KW_ONLY, {.u_int = 1} },
     };
     mp_arg_val_t args[MP_ARRAY_SIZE(allowed_args)];
     mp_arg_parse_all_kw_array(n_args, n_kw, all_args, MP_ARRAY_SIZE(allowed_args), allowed_args, args);
@@ -85,8 +89,13 @@ static mp_obj_t mtm_hardware_dacout_make_new(const mp_obj_type_t *type, size_t n
     const mcu_pin_obj_t *mosi = validate_obj_is_free_pin(args[ARG_mosi].u_obj, MP_QSTR_mosi);
     const mcu_pin_obj_t *cs = validate_obj_is_free_pin(args[ARG_cs].u_obj, MP_QSTR_cs);
 
+    mp_int_t gain = args[ARG_gain].u_int;
+    if (gain != 1 && gain != 2) {
+        mp_raise_ValueError(MP_COMPRESSED_ROM_TEXT("gain must be 1 or 2"));
+    }
+
     mtm_hardware_dacout_obj_t *self = mp_obj_malloc_with_finaliser(mtm_hardware_dacout_obj_t, &mtm_hardware_dacout_type);
-    common_hal_mtm_hardware_dacout_construct(self, clock, mosi, cs);
+    common_hal_mtm_hardware_dacout_construct(self, clock, mosi, cs, (uint8_t)gain);
 
     return MP_OBJ_FROM_PTR(self);
 }