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3b2: Properly initialize DMAC Current Word Count

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- The DMAC controller "Current Word Count" expects to decrement
  beyond 0 to 0xffff. Its initial value should also be 0xffff.
  Setting the initial value to 0 introduced a very subtle bug
  related to DUART self-test following a soft power reset.
This commit is contained in:
Seth Morabito 2018-12-13 19:39:21 -08:00
parent 7c207c6233
commit 6e7127d954
1 changed files with 3 additions and 3 deletions
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6
3B2/3b2_dmac.c
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@ -79,7 +79,7 @@ t_stat dmac_reset(DEVICE *dptr)
dma_state.channels[i].addr = 0; dma_state.channels[i].addr = 0;
dma_state.channels[i].wcount = 0; dma_state.channels[i].wcount = 0;
dma_state.channels[i].addr_c = 0; dma_state.channels[i].addr_c = 0;
dma_state.channels[i].wcount_c = 0; dma_state.channels[i].wcount_c = -1;
dma_state.channels[i].ptr = 0; dma_state.channels[i].ptr = 0;
} }
@ -282,7 +282,7 @@ void dmac_program(uint8 reg, uint8 val)
dma_state.channels[i].addr = 0; dma_state.channels[i].addr = 0;
dma_state.channels[i].wcount = 0; dma_state.channels[i].wcount = 0;
dma_state.channels[i].addr_c = 0; dma_state.channels[i].addr_c = 0;
dma_state.channels[i].wcount_c = 0; dma_state.channels[i].wcount_c = -1;
dma_state.channels[i].ptr = 0; dma_state.channels[i].ptr = 0;
} }
break; break;
@ -372,7 +372,7 @@ void dmac_generic_dma(uint8 channel, uint32 service_address)
uint32 addr; uint32 addr;
dma_channel *chan = &dma_state.channels[channel]; dma_channel *chan = &dma_state.channels[channel];
i = (int32) chan->wcount_c; i = chan->wcount_c;
/* TODO: This does not handle decrement-mode transfers, /* TODO: This does not handle decrement-mode transfers,
which don't seem to be used in SVR3 */ which don't seem to be used in SVR3 */