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Diffstat (limited to 'src/mess/machine/coco.c')
-rw-r--r--src/mess/machine/coco.c50
1 files changed, 33 insertions, 17 deletions
diff --git a/src/mess/machine/coco.c b/src/mess/machine/coco.c
index 7994f5b9caa..d28fa1b3412 100644
--- a/src/mess/machine/coco.c
+++ b/src/mess/machine/coco.c
@@ -183,6 +183,7 @@ void coco_state::device_reset()
/* reset state */
m_dac_output = 0;
+ m_analog_audio_level = 0;
m_hiresjoy_ca = false;
m_dclg_previous_bit = false;
m_dclg_output_h = 0;
@@ -364,7 +365,7 @@ WRITE8_MEMBER( coco_state::pia0_pb_w )
WRITE_LINE_MEMBER( coco_state::pia0_ca2_w )
{
- update_sound();
+ update_sound(); // analog mux SEL1 is tied to PIA0 CA2
poll_keyboard();
}
@@ -376,7 +377,7 @@ WRITE_LINE_MEMBER( coco_state::pia0_ca2_w )
WRITE_LINE_MEMBER( coco_state::pia0_cb2_w )
{
- update_sound();
+ update_sound(); // analog mux SEL2 is tied to PIA0 CB2
poll_keyboard();
}
@@ -456,6 +457,8 @@ WRITE8_MEMBER( coco_state::ff20_write )
READ8_MEMBER( coco_state::pia1_pa_r )
{
+ // Port A: we need to specify the values of all the lines, regardless of whether
+ // they are in input or output mode in the DDR
return (m_cassette->input() >= 0 ? 0x01 : 0x00)
| (dac_output() << 2);
}
@@ -470,6 +473,8 @@ READ8_MEMBER( coco_state::pia1_pa_r )
READ8_MEMBER( coco_state::pia1_pb_r )
{
+ // Port B: lines in output mode are handled automatically by the PIA object.
+ // We only need to specify the input lines here
UINT32 ram_size = m_ram->size();
// For the CoCo 1, the logic has been changed to only select 64K rams
@@ -479,7 +484,7 @@ READ8_MEMBER( coco_state::pia1_pb_r )
// to access 32K of ram, and also allows the cocoe driver to access
// the full 64K, as this uses Color Basic 1.2, which can configure 64K rams
bool memory_sense = (ram_size >= 0x4000 && ram_size <= 0x7FFF)
- || (ram_size >= 0x8000 && (m_pia_0->b_output() & 0x80));
+ || (ram_size >= 0x8000 && (m_pia_0->b_output() & 0x40));
// serial in (PB0)
bool serial_in = (m_rs232 != NULL) && (m_rs232->rxd_r() ? true : false);
@@ -497,7 +502,7 @@ READ8_MEMBER( coco_state::pia1_pb_r )
WRITE8_MEMBER( coco_state::pia1_pa_w )
{
- pia1_pa_changed();
+ pia1_pa_changed(data);
}
@@ -508,7 +513,7 @@ WRITE8_MEMBER( coco_state::pia1_pa_w )
WRITE8_MEMBER( coco_state::pia1_pb_w )
{
- pia1_pb_changed();
+ pia1_pb_changed(data);
}
@@ -532,11 +537,7 @@ WRITE_LINE_MEMBER( coco_state::pia1_ca2_w )
WRITE_LINE_MEMBER( coco_state::pia1_cb2_w )
{
- poll_keyboard();
-
- // Theoretically, I should be calling update_sound() here; however this seems to create
- // a buzzing in some CoCo software (e.g. - Popcorn). This is likely because this line
- // drives the MC14529B MUX, and when disabled the output probably goes hi-Z.
+ update_sound(); // SOUND_ENABLE is connected to PIA1 CB2
}
@@ -689,10 +690,25 @@ void coco_state::update_sound(void)
UINT8 cassette_sound = (bCassSoundEnable ? 0x40 : 0);
UINT8 cart_sound = (bCartSoundEnable ? 0x40 : 0);
- /* determine the value to send to the DAC */
+ /* determine the value to send to the DAC (this is used by the Joystick read as well as audio out) */
m_dac_output = (m_pia_1->a_output() & 0xFC) >> 2;
UINT8 dac_sound = (status == SOUNDMUX_ENABLE ? m_dac_output << 1 : 0);
- m_dac->write_unsigned8(single_bit_sound + dac_sound + cassette_sound + cart_sound);
+
+ /* The CoCo uses a single DAC for both audio output and joystick axis position measurement.
+ * To avoid introducing artifacts while reading the axis positions, some software will disable
+ * the audio output while using the DAC to read the joystick. On a real CoCo, there is a low-pass
+ * filter (C57 on the CoCo 3) which will hold the audio level for very short periods of time,
+ * preventing the introduction of artifacts while the joystick value is being read. We are not going
+ * to simulate the exponential decay of a capacitor here. Instead, we will store and hold the last
+ * used analog audio output value while the audio is disabled, to avoid introducing artifacts in
+ * software such as Tandy's Popcorn and Sock Master's Donkey Kong.
+ */
+ if ((status & SOUNDMUX_ENABLE) != 0)
+ {
+ m_analog_audio_level = dac_sound + cassette_sound + cart_sound;
+ }
+
+ m_dac->write_unsigned8(single_bit_sound + m_analog_audio_level);
/* determine the cassette sound status */
cassette_state cas_sound = bCassSoundEnable ? CASSETTE_SPEAKER_ENABLED : CASSETTE_SPEAKER_MUTED;
@@ -981,12 +997,12 @@ void coco_state::update_prinout(bool prinout)
// pia1_pa_changed - called when PIA1 PA changes
//-------------------------------------------------
-void coco_state::pia1_pa_changed(void)
+void coco_state::pia1_pa_changed(UINT8 data)
{
- update_sound();
+ update_sound(); // DAC is connected to PIA1 PA2-PA7
poll_keyboard();
update_cassout(dac_output());
- update_prinout(m_pia_1->a_output() & 0x02 ? true : false);
+ update_prinout(data & 0x02 ? true : false);
}
@@ -995,9 +1011,9 @@ void coco_state::pia1_pa_changed(void)
// pia1_pb_changed - called when PIA1 PB changes
//-------------------------------------------------
-void coco_state::pia1_pb_changed(void)
+void coco_state::pia1_pb_changed(UINT8 data)
{
- update_sound();
+ update_sound(); // singe_bit_sound is connected to PIA1 PB1
}