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Gowin. Bugfix.

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The statement in the Gowin documentation that in the reading mode
"READ_MODE=0" the output register is not used and the OCE signal is
ignored is not confirmed by practice - if the OCE was left unconnected
or connected to the constant network, then a change in output data was
observed even with CE=0, as well as the absence of such at CE=1.

Synchronizing CE and OCE helps and the memory works properly in complex
systems such as RISC-V emulation and i8080 emulation (with 32K RAM and
16K BSRAM based ROM), but there is no theoretical basis for this fix, so
it is a hack.

Signed-off-by: YRabbit <rabbit@yrabbit.cyou>
This commit is contained in:
YRabbit 2024-07-09 09:42:35 +10:00 committed by myrtle
parent 1871afe9b9
commit eb099a9244
1 changed files with 12 additions and 6 deletions
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16
himbaechel/uarch/gowin/pack.cc
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@ -1612,10 +1612,10 @@ struct GowinPacker
ci->connectPort(id_WREB, vcc_net);
// disconnect lower address bits for ROM
static int rom_ignore_bits[] = {2, 4, 8, 16, 32};
static int romx9_ignore_bits[] = {9, 9, 9, 18, 36};
std::array rom_ignore_bits = {2, 4, 8, 16, 32};
std::array romx9_ignore_bits = {9, 9, 9, 18, 36};
for (unsigned int i = 0; i < 14; ++i) {
if (i < sizeof(rom_ignore_bits) && ((ci->type == id_pROM && bit_width >= rom_ignore_bits[i]) ||
if (i < size(rom_ignore_bits) && ((ci->type == id_pROM && bit_width >= rom_ignore_bits[i]) ||
(ci->type == id_pROMX9 && bit_width >= romx9_ignore_bits[i]))) {
ci->disconnectPort(ctx->idf("AD[%d]", i));
} else {
@ -1823,13 +1823,19 @@ struct GowinPacker
bsram_fix_blksel(ci, new_cells);
}
// XXX
// The statement in the Gowin documentation that in the reading mode
// "READ_MODE=0" the output register is not used and the OCE signal is
// ignored is not confirmed by practice - if the OCE was left
// unconnected or connected to the constant network, then a change in
// output data was observed even with CE=0, as well as the absence of
// such at CE=1.
// Synchronizing CE and OCE helps but it's definitely a hack.
NetInfo *oce_net = ci->getPort(id_OCE);
if (oce_net == nullptr || oce_net->name == ctx->id("$PACKER_VCC") || oce_net->name == ctx->id("$PACKER_GND")) {
if (oce_net != nullptr) {
ci->disconnectPort(id_OCE);
ci->copyPortTo(id_CE, ci, id_OCE);
}
ci->copyPortTo(id_CE, ci, id_OCE);
}
// XXX UG285-1.3.6_E Gowin BSRAM & SSRAM User Guide: