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machine/ncr53c90.cpp: Fix NCR53CF94 ID read sequence

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This commit is contained in:
AJR 2025-01-06 23:07:44 -05:00
parent 2a9cfda080
commit fd93123881
2 changed files with 22 additions and 9 deletions
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28
src/devices/machine/ncr53c90.cpp
View File

@ -918,6 +918,15 @@ void ncr53c90_device::command_pop_and_chain()
} }
} }
void ncr53c90_device::load_tcounter()
{
LOGMASKED(LOG_COMMAND, "DMA command: tcounter reloaded to %d\n", tcount & tcounter_mask);
tcounter = tcount & tcounter_mask;
// clear transfer count zero flag when counter is reloaded
status &= ~S_TC0;
}
void ncr53c90_device::start_command() void ncr53c90_device::start_command()
{ {
uint8_t c = command[0] & 0x7f; uint8_t c = command[0] & 0x7f;
@ -932,11 +941,7 @@ void ncr53c90_device::start_command()
dma_command = command[0] & 0x80; dma_command = command[0] & 0x80;
if (dma_command) if (dma_command)
{ {
LOGMASKED(LOG_COMMAND, "DMA command: tcounter reloaded to %d\n", tcount); load_tcounter();
tcounter = tcount;
// clear transfer count zero flag when counter is reloaded
status &= ~S_TC0;
} }
else else
{ {
@ -1417,6 +1422,15 @@ void ncr53cf94_device::device_reset()
ncr53c94_device::device_reset(); ncr53c94_device::device_reset();
} }
void ncr53cf94_device::load_tcounter()
{
ncr53c94_device::load_tcounter();
// ID may be read by executing DMA NOP command twice, first with the features bit clear and then with it set
if ((config2 & S2FE) == 0)
tcount = (1 << 23) | (family_id << 19) | (revision_level << 16) | (tcount & 0xffff);
}
void ncr53cf94_device::conf2_w(uint8_t data) void ncr53cf94_device::conf2_w(uint8_t data)
{ {
tcounter_mask = (data & S2FE) ? 0xffffff : 0xffff; tcounter_mask = (data & S2FE) ? 0xffffff : 0xffff;
@ -1425,10 +1439,6 @@ void ncr53cf94_device::conf2_w(uint8_t data)
uint8_t ncr53cf94_device::tcounter_hi2_r() uint8_t ncr53cf94_device::tcounter_hi2_r()
{ {
// tcounter is 24-bit when the features bit is set, otherwise it returns the ID
if ((config2 & S2FE) == 0)
return (1 << 7) | (family_id << 3) | revision_level;
LOG("tcounter_hi2_r %02x (%s)\n", (tcounter >> 16) & 0xff, machine().describe_context()); LOG("tcounter_hi2_r %02x (%s)\n", (tcounter >> 16) & 0xff, machine().describe_context());
return tcounter >> 16; return tcounter >> 16;
} }

3
src/devices/machine/ncr53c90.h
View File

@ -232,6 +232,7 @@ protected:
void delay_cycles(int cycles); void delay_cycles(int cycles);
void decrement_tcounter(int count = 1); void decrement_tcounter(int count = 1);
virtual void load_tcounter();
devcb_write_line m_irq_handler; devcb_write_line m_irq_handler;
devcb_write_line m_drq_handler; devcb_write_line m_drq_handler;
@ -361,6 +362,8 @@ protected:
virtual void device_start() override ATTR_COLD; virtual void device_start() override ATTR_COLD;
virtual void device_reset() override ATTR_COLD; virtual void device_reset() override ATTR_COLD;
virtual void load_tcounter() override;
private: private:
u8 config4; u8 config4;
u8 family_id; u8 family_id;