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z80dma: Implemented the byte counter as an up counter. [Curt Coder]

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abc1600 expects an up counter, and checks that the byte counter value is 0x200 after transferring 0x200 bytes.
This is corroborated by the Z-80 DMA Controller Product Specification (February 1980) on page 7.
This commit is contained in:
Curt Coder 2022-03-01 18:36:56 +02:00
parent 40a83e5b7f
commit a5c7805f81
2 changed files with 10 additions and 4 deletions
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13
src/devices/machine/z80dma.cpp
View File

@ -197,6 +197,7 @@ void z80dma_device::device_start()
save_item(NAME(m_addressA));
save_item(NAME(m_addressB));
save_item(NAME(m_count));
save_item(NAME(m_byte_counter));
save_item(NAME(m_rdy));
save_item(NAME(m_force_ready));
save_item(NAME(m_is_read));
@ -485,6 +486,7 @@ int z80dma_device::do_write()
m_addressA += PORTA_FIXED ? 0 : PORTA_INC ? 1 : -1;
m_addressB += PORTB_FIXED ? 0 : PORTB_INC ? 1 : -1;
m_byte_counter++;
m_count--;
done = (m_count == 0xFFFF); //correct?
@ -551,6 +553,7 @@ TIMER_CALLBACK_MEMBER(z80dma_device::timerproc)
m_addressA = PORTA_ADDRESS;
m_addressB = PORTB_ADDRESS;
m_count = BLOCKLEN;
m_byte_counter = 0;
m_status |= 0x30;
}
}
@ -713,8 +716,8 @@ void z80dma_device::write(uint8_t data)
LOG("Z80DMA Initiate Read Sequence\n");
m_read_cur_follow = m_read_num_follow = 0;
if(READ_MASK & 0x01) { m_read_regs_follow[m_read_num_follow++] = m_status; }
if(READ_MASK & 0x02) { m_read_regs_follow[m_read_num_follow++] = m_count & 0xff; } //byte counter (low)
if(READ_MASK & 0x04) { m_read_regs_follow[m_read_num_follow++] = m_count >> 8; } //byte counter (high)
if(READ_MASK & 0x02) { m_read_regs_follow[m_read_num_follow++] = m_byte_counter & 0xff; } //byte counter (low)
if(READ_MASK & 0x04) { m_read_regs_follow[m_read_num_follow++] = m_byte_counter >> 8; } //byte counter (high)
if(READ_MASK & 0x08) { m_read_regs_follow[m_read_num_follow++] = m_addressA & 0xff; } //port A address (low)
if(READ_MASK & 0x10) { m_read_regs_follow[m_read_num_follow++] = m_addressA >> 8; } //port A address (high)
if(READ_MASK & 0x20) { m_read_regs_follow[m_read_num_follow++] = m_addressB & 0xff; } //port B address (low)
@ -744,6 +747,7 @@ void z80dma_device::write(uint8_t data)
m_addressA = PORTA_ADDRESS;
m_addressB = PORTB_ADDRESS;
m_count = BLOCKLEN;
m_byte_counter = 0;
m_status |= 0x30;
LOG("Z80DMA Load A: %x B: %x N: %x\n", m_addressA, m_addressB, m_count);
@ -764,6 +768,7 @@ void z80dma_device::write(uint8_t data)
case COMMAND_CONTINUE:
LOG("Z80DMA Continue\n");
m_count = BLOCKLEN;
m_byte_counter = 0;
m_dma_enabled = 1;
//"match not found" & "end of block" status flags zeroed here
m_status |= 0x30;
@ -831,8 +836,8 @@ void z80dma_device::write(uint8_t data)
m_read_cur_follow = m_read_num_follow = 0;
if(READ_MASK & 0x01) { m_read_regs_follow[m_read_num_follow++] = m_status; }
if(READ_MASK & 0x02) { m_read_regs_follow[m_read_num_follow++] = m_count & 0xff; } //byte counter (low)
if(READ_MASK & 0x04) { m_read_regs_follow[m_read_num_follow++] = m_count >> 8; } //byte counter (high)
if(READ_MASK & 0x02) { m_read_regs_follow[m_read_num_follow++] = m_byte_counter & 0xff; } //byte counter (low)
if(READ_MASK & 0x04) { m_read_regs_follow[m_read_num_follow++] = m_byte_counter >> 8; } //byte counter (high)
if(READ_MASK & 0x08) { m_read_regs_follow[m_read_num_follow++] = m_addressA & 0xff; } //port A address (low)
if(READ_MASK & 0x10) { m_read_regs_follow[m_read_num_follow++] = m_addressA >> 8; } //port A address (high)
if(READ_MASK & 0x20) { m_read_regs_follow[m_read_num_follow++] = m_addressB & 0xff; } //port B address (low)

1
src/devices/machine/z80dma.h
View File

@ -118,6 +118,7 @@ private:
uint16_t m_addressA;
uint16_t m_addressB;
uint16_t m_count;
uint16_t m_byte_counter;
int m_rdy;
int m_force_ready;